Accurate measurements of knee joint motion during gait after anterior cruciate ligament reconstruction (ACLR), especially for the patellofemoral joint, are sparse. The aim of this study was to measure six-degree-of-freedom (6-DOF) patellofemoral and tibiofemoral motion in ACLR and uninjured contralateral knees during gait, and to compare these results to healthy (control) knees. Biplane fluoroscopy was used to measure 6-DOF patellofemoral and tibiofemoral motion in 15 ACLR participants (26.3 ± 3.9 years) for complete cycles of level walking and downhill walking, and the results were compared to data for 10 healthy individuals (29.8 ± 6.1 years). Mean patellar superior translation, anterior translation, and flexion over the gait cycle were respectively 4.4-5.6 mm greater, 5.4-6.3 mm greater, and 3.7°-7.0° less in the ACLR and contralateral knees compared to controls across both activities (p < 0.021). Articular contact was 7.6 mm higher on the femoral trochlea in the ACLR and contralateral knees compared to controls. The patellar tendon was 8.9 mm longer (p < 0.001) in the ACLR and contralateral knees compared to controls. Among ACLR participants, 14 out of 30 knees (47%) had an Insall-Salvati ratio ≥ 1.20, indicating patella alta. Mean tibial external rotation and anterior translation over the gait cycle were respectively 3.4°-3.8° greater and 2.6-3.0 mm greater in the ACLR knee compared to controls across both activities (p < 0.025). A high-riding patella in both knees of the ACLR participants was due to a longer patellar tendon. A change in the load-bearing areas of the femoral trochlea may contribute to the high rate of patellofemoral osteoarthritis seen after ACLR.

As patella height can affect the outcome of total knee arthroplasty (TKA) in a number of ways, this study aimed to investigate whether factors such as region, sex and age play a role in causing differences in patella height.

Between the 1st of March and the 31st of December 2022, 2000 patients from 7 different countries (Turkey, Saudi Arabia, Germany, Austria, Italy, Spain, and the United Kingdom) awaiting elective TKA were enrolled in this study. Lateral radiographs of the knee with the femoral condyles fully overlapped were used to measure the Insall-Salvati index. The patella height measurements were then correlated with age, sex and region to see if there were any patterns of distribution.

From ten different hospitals across seven countries, 2,000 patients were collected. Approximately, 50% of the groups were female and 50% were male with a median age at surgery of 59 years (± 20 years). There were no significant differences in patella position based on age, region or sex between the different study populations, although there were significant differences between patients from different countries.

Patella height showed significant variability within our patient cohort, even between different populations within the same country of origin. However, it should be noted that age, sex and country of origin do not appear to influence patella height in the preoperative planning of knee surgery.

Patellar height (PH) constitutes an important component of patellofemoral biomechanics. Iatrogenic decrease in PH after knee procedures has been demonstrated for arthroplasty and high tibial osteotomy, among others. However, alterations in PH resulting from tibial tubercle osteotomy (TTO) have yet to be described.

This study aimed to compare pre- and postoperative PH ratios and patellar tendon length (PL) in adult patients who have received an anteromedialization or medialization TTO. The authors hypothesized that TTO would result in PH alterations with trends toward patella baja.

Case series; Level of evidence, 4.

This was a retrospective review of adult patients receiving primary TTO +/- medial patellofemoral ligament reconstruction from 2013 to 2020. All patients had a minimum 6-month radiographic follow-up. Pre- and postoperative PH measurements were assessed with the Blackburne-Peel Index (BPI), Caton-Deschamps Index (CDI), Insall-Salvati Ratio (ISR), and PL. Paired t tests were performed for each measurement index comparing pre- and postoperative radiographs.

A total of 42 patients (64% women), with a mean age of 26.5 years (range, 18-51 years) and a mean radiographic follow-up of 19 months (6 -110 months) met the inclusion criteria. The mean preoperative PH using the BPI, CDI, and ISR were 0.99 ± 0.239, 1.20 ± 0.240, and 1.29 ± 0.206, respectively. The mean preoperative PL was 54.52 ± 7.23 mm. The mean postoperative PH using the BPI, CDI, and ISR were 0.95 ± 0.24, 1.16 ± 0.21, and 1.20 ± 0.19, respectively. The mean postoperative PL was 52.79 ± 7.25 mm. The mean differences between the pre- and postoperative were as follows: BPI: 0.04; CDI: 0.04; ISR: 0.08; and PL: 1.73 mm, none of which were statistically significant.

While changes were observed in approximately 50% of patients, there were no statistically significant, nor predictable, alterations in PH after TTO using the BPI, CDI, ISR, or PL measurements at a minimum 6-month follow-up. Further large-scale studies are needed to determine the reliability of these PH findings and whether the changes are clinically impactful on surgeon decision-making and patient outcomes.

The vascularity of the quadriceps tendon influences the risk of tendon rupture. Quadriceps and patellar tendon ruptures are rare but serious injuries, with an incidence of 1.37/100000 and 0.68/100000, respectively. Risk factors include age, degeneration, and systemic diseases such as kidney disease and rheumatoid arthritis. While quadriceps tendon ruptures predominantly affect people over 50, patellar tendon ruptures are more common in younger, physically active people, often with pre-existing tendon pathologies. The most common mechanism of rupture of the quadriceps tendon is indirect trauma, typically caused by sudden eccentric loading or reflexive contraction, with degeneration of the tendon tissue being a predisposing factor. Diagnosis is primarily clinical, supported by imaging modalities such as ultrasound and MRI. Treatment options depend on the severity of the tear. Partial ruptures can often be managed conservatively, whereas complete ruptures require surgical repair, typically by transosseous suture or fixation with bone anchors or transosseous sutures. Early functional rehabilitation is essential for optimal recovery. The prognosis is generally favorable with early treatment, although complications such as quadriceps atrophy and flexion deficits may occur. Proper documentation of the mechanism of injury and histopathological evaluation of the tendon tissue are important to determine the underlying cause and ensure appropriate insurance coverage.

To investigate the correlation between 3D shiftactive extension (lateral patellar shift in active extension position based on newly established 3D measurement method) and static tibial tubercle-trochlear groove (TT-TG) distance in full knee extension with muscle relaxation.

42 knees of 24 patients with recurrent patellar dislocation were included in the study group and 38 knees of 30 subjects were included in the control group. TT-TG distance, bisect offset indexmuscle relaxation, bisect offset indexactive extension and 3D shiftactive extension were measured to investigate the correlation between patellar lateral shift measurements and TT-TG distance.

In the recurrent patellar dislocation group, the correlation between TT-TG distance and 3D shiftactive extension (r = 0.76 [95 % CI, 0.61 to 0.86]) was significantly higher than correlation between TT-TG distance and bisect offset indexactive extension (r = 0.61 [95 % CI, 0.32 to 0.79]) and correlation between TT-TG distance and bisect offset indexmuscle relaxation (r = 0.6 [95 % CI, 0.32 to 0.80]), with p = 0.01 and p = 0.03, respectively.

Significantly stronger correlation between TT-TG distance and 3D shiftactive extension in patients with patellar dislocation was observed in this study. 3D shiftactive extension could be considered as a preoperative evaluation for tibial tubercle osteotomy to both characterize the patellar lateral shift and estimate tibial tubercle lateralization to simplify the preoperative assessment procedures. The 3D shiftactive extension obtained under muscle contraction conditions both simulated the functional state of the patellofemoral joint and improved the limitations of the 2D measurements, helping to improve surgical decision-making for functional rehabilitation.

Level III.

An excessive posterior tibial slope (PTS) is a risk factor for anterior cruciate ligament (ACL) rupture or rerupture, and it can be managed by an anterior closing wedge high tibial osteotomy (ACW-HTO). The effect of slope-changing osteotomies on patellar height is poorly described after infratuberosity ACW-HTO.

To assess the effect of ACW-HTO on patellar height using an infratuberosity approach.

Case series; Level of evidence, 4.

Patients who underwent ACW-HTO between January 2019 and March 2024 were assessed for eligibility. Among 98 cases, 94 knees were analyzed with a complete radiographic assessment for the patellar height evaluation. Patellar height was measured on lateral radiographs according to the Caton-Deschamps index (CDI), Insall-Salvati index (ISI), and Blackburne-Peel index (BPI). The change in patellar height was assessed postoperatively, as were the rates of cases with a postoperative difference <0.3, <0.5, or >0.5 points of the respective index. The change in patellar height category (baja, normal, or alta) after correction of the PTS was also evaluated.

In univariate analysis, no significant difference was found between pre- and postoperative radiographs for the patellar height indices (differences for ISI: +0.1 ± 0.1, P = .18; CDI: +0.1 ± 0.1, P = .41; BPI: +0.1 ± 0.2, P = .52). The patellar height variation was +0.5 points in only 1 case for CDI, and it was <0.5 points in all other cases (98.9%). Five cases (5.3%) exhibited a postoperative change in patellar height category when measured by the ISI (3 moved up a category, 2 moved down a category; P = .65). Eight cases (8.5%) changed category according to the CDI (6 moved up a category, 2 moved down a category; P = .14). Twelve cases (12.7%) changed category according to the BPI (7 moved up a category, 5 moved down a category; P = .55).

Infratuberosity ACW-HTO for tibial slope correction did not lead to significant changes in patellar height. However, slight variations in both directions were possible in a small portion of patients.

Consequences of osteochondral fractures associated with patellar dislocation can be severe for younger patients. Precise 3-dimensional characterization of fracture location, size, frequency, and radiographic associations remain undefined in this population.

(1) To define the topographic characteristics of osteochondral fractures in pediatric and adolescent patients with first-time patellar dislocations and (2) to determine the relationship between these characteristics and radiographic and patient factors.

Cross-sectional study; Level of evidence, 3.

A retrospective observational study was conducted between 2015 and 2023 of consecutive patients aged <18 years undergoing surgical intervention for displaced osteochondral fractures in the setting of first-time patellar dislocation. Three-dimensional location and relative injury frequency were quantified with heat map analysis. Subgroup analysis of intraoperative osteochondral fracture size and location was conducted using chi-square testing and an independent t test at an alpha of .05.

The study cohort included 82 knees (80 patients) with first-time patellar dislocation and osteochondral fracture. A total of 97 osteochondral fractures were identified, with the lateral femur as the most common fracture site at 55% (n = 53), as compared with 43% (n = 42) for the patella and 2% (n = 2) for the lateral trochlea. Patellar osteochondral fractures were significantly larger than femoral lesions (mean ± SD, 258 ± 168 mm2 vs 126 ± 109 mm2; P < .001) and more amenable to fixation than femoral osteochondral fractures (fixation, 57.1% [n = 24] vs 15.1% [n = 8]; P < .001). Patellar and femoral osteochondral fractures were >100 mm2 in 78.6% (n = 33) and 32.1% (n = 17) of lesions, respectively. Patellar mean fracture size was significantly larger in the group with a tibial tubercle-trochlear groove distance <20 mm (P = .018). The mean osteochondral fracture size of the lateral femoral condyle was significantly larger in the open physis group as compared with the closed physis group (P = .027).

We found that the most common site for osteochondral fracture was the femur, although patellar osteochondral fractures were significantly larger. Factors that affect anatomic structure and ligamentous laxity appear to contribute to patterns of osteochondral fractures.

The patella fracture involving of inferior pole fractures (IPF) may be associated with patella baja, However, the clinical impact of this condition remains unclear. This study aims to clarify 1) the incidence of patella baja following patellar fracture surgery, 2) the associated clinical outcomes with and without the presence of patella baja, and 3) the potential correlation between the detection of IPF on CT and the occurrence of patella baja.

We conducted a retrospective multicenter study involving 251 patients who underwent surgical treatment for patellar fractures. Patients were divided into the patella baja (PB; n = 49) group and patella norma (PN; n = 202) group. Data collected included demographics, radiographic findings, surgical details, and postoperative complications. We compared these items between PB group and PN group. Logistic regression analyses were used to identify risk factors for patella baja.

Immediately following surgery, 36 (14.3%) patients presented with patella baja which increased to 49 cases (19.5%) at six months postoperatively. There is no statistically significant difference in the demographics, surgical details, clinical outcomes and complication between PB group and PN group. While, in the radiographical assessment, the prevalence of IPF on CT scan in the patella baja group was significantly higher than that in the patella norma group. By logistic regression analysis, IPFP on CT was identified as an independent risk factor for patella baja. (odds ratio 2.11, 95% confidence interval: 1.03-4.33, p = 0.042).

In patients with patellar fractures, the incidence of patella baja increased from 14.3% immediately post-surgery to 19.5% at the six-month check-up. No significant differences were observed in clinical outcomes between the patella baja group and the norma group. The patella fracture involving IPF on CT emerged as a predictive factor for patella baja.

Magnetic resonance imaging (MRI) is often used to evaluate patients with patellar dislocations to facilitate diagnosis and management strategies. Many radiological parameters have been described in the literature. The aim of this study was to assess the significance of tibial-tubercle trochlear groove distance (TT-TG) distance and other MRI measurements in patients with and without patellar instability.

This case-control study included 41 patients with recurrent patellar instability and 50 patients with stable knees, all of whom underwent MRI scans. A total of 19 radiological parameters were measured in both groups.

All measured MRI parameters had statistically significant differences between both groups (p < 0.05) apart from trochlear cartilage length. TT-TG distance. 20 mm had the strongest association with patellar instability (OR 53.3, p = 0.006, 95%CI [3.1- 927.4]) and the highest specificity (100%) but had the lowest sensitivity (34%) out of all the measured parameters. TT-TG. 13 mm had a higher sensitivity (68%) but lower specificity (72%) and weaker association with patellar instability (OR 5.5, p < 0.001, 95%CI [2.2. 13.7]). TT-TG/trochlear articular cartilage width ratio also had a strong association with patellar instability (OR 14.7, p < 0.001, 95%CI [4.5. 48.5]) with high specificity (92%) but lower sensitivity (56%).

The cut-off values for TT-TG distance at 13 mm and 20 mm both had advantages and disadvantages which supports the concept of using patient-individualised ratios. Patellar instability is associated with many radiological abnormalities demonstrated on MRI scans. Selection of the most appropriate measurement is dependent on the philosophy and preference of the treating clinician.

Conservative treatment remains the standard approach for first-time patellar dislocations. While risk factors for patellofemoral instability, a common paediatric injury, are well-established in adults, data concerning the progression of paediatric recurrent patellar dislocation remain scarce. A reproducible method was developed to quantitatively assess the patellofemoral morphology and anatomic risk factors in paediatric patients using magnetic resonance imaging (MRI) and machine learning analysis.

Data were analyzed from a retrospective review (2005-2022) of paediatric patients diagnosed with acute lateral patellar dislocation (54 patients) who underwent MRI and were compared with an age-based control group (54 patients). Patellofemoral, tibial, tibiofemoral and patellar height parameters were measured. Differences between groups were analyzed with respect to MRI parameters. The potential diagnostic utility of the parameters was assessed via machine learning and genetic algorithm analyses.

Significant differences were observed between the two groups in six patellofemoral morphological parameters. Regarding patellar height morphological parameters, all methods exhibited significant between-group differences. Among the tibia and tibiofemoral morphological parameters, only the tibial tubercle-trochlear groove distance exhibited significant differences between the two groups. No sex-related differences were present. Significant variations were observed in patellar height parameters, particularly in the Koshino-Sugimoto (KS) index, which had the highest area under the curve (AUC: 0.87). Using genetic algorithms and logistic regression, our model excelled with seven key independent variables.

KS index and Wiberg index had the strongest association with lateral patellar dislocation. An optimized logistic regression model achieved an AUC of 0.934. Such performance is considered clinically relevant, indicating the model's effectiveness for the intended application.

Level Ⅲ.

Patella alta, which describes an abnormally proximally positioned patella, has become of particular interest as it has been identified as a potential factor in patellofemoral instability (PFI) and other common pediatric orthopedic conditions. The purpose of this review is to describe the condition, measuring techniques, and its association with pediatric orthopedic conditions, and to evaluate methods of correction of patella alta.

Recent literature has explored the etiology of patella alta by investigating patellar height as age increases, with inconclusive findings as to whether the condition is congenital or acquired over time. Additionally, patella alta has been identified to be associated with several pediatric orthopedic conditions, including PFI, anterior knee pain, and cerebral palsy. As such, methods of correction for patella alta, including medial patellofemoral ligament reconstruction (MPFLR), tibial tubercle distalization, and patella tendon imbrication, have been studied.

Patella alta, defined by an abnormally high patellar height, is associated with patellofemoral instability, anterior knee pain, and cerebral palsy. Various indices have been developed to measure and define patellar height, including the Caton-Deschamps Index and Koshino-Sugimoto Index which are applicable to a pediatric population. Treatments include isolated or concomitant MPFLR, distalizing tibial tubercle osteotomy, and patella tendon imbrication, which have shown success in reducing patellar height and improving patella alta, though risks for complications do exist.

To evaluate the radiological and clinical outcomes in two patient groups: first, varus aligned medial meniscus posterior root tear (MMPRT) patients who underwent posteromedial open wedge high tibial osteotomy (PMOWHTO) and simultaneous root repair; second, patients with varus medial knee osteoarthritis without MMPRT who underwent PMOWHTO.

Patients had MMPRT repair concomitant with PMOWHTO and varus medial knee osteoarthritis without concomitant root tear patients who underwent PMOWHTO and were reviewed. Radiographic parameters, medial meniscus extrusion (MME) and Knee Society Scores [KSSs, including the following subscores: knee score (KS) and knee function score (KFS)] were evaluated. Continious variables are expressed as the median and interquartile range (IQR) [IQR: (Q1;Q3); Q1: median of lower half, Q3: median of upper half]. The minimum follow-up period was 24 months [29 (28;35) months].

A total of 36 knees of 34 patients underwent PMOWHTO were included. Patients were divided into two groups according to the presence or absence of a MMPRT. Nineteen of the 36 knees had MMPRTs, and all of them had concomitant root repair (Group 1). Seventeen of the 36 patients did not have MMPRTs (Group 2). The posterior tibial slope (PTS) decreased postoperatively in a total of 36 knees (p < 0.001). There were no significant changes in MME postoperatively in any intragroup comparison. The preoperative and follow-up MMEs of Group 1 were greater than those of Group 2 (p < 0.001). The KSs and KFSs in both Group 1 and Group 2 increased during follow-up [KS; Group 1: 43 (36;53) vs. 86 (84;95), p < 0.001. Group 2: 49 (45;57) vs. 89 (80;93), p < 0.001. KFS; Group 1: 60 (50;60) vs. 90 (80;100), p < 0.001. Group 2: 60 (50;60) vs. 80 (80;90), p < 0.001]. All knees achieved minimal clinically important difference (MCID) in terms of KSs. Eighteen (95%) knees achieved MCID in Group 1, and 17 (100%) achieved MCID in Group 2 in terms of KFSs. There were no differences between Groups 1 and 2 in terms of preoperative and follow-up KSs or preoperative KFSs. The follow-up KFSs in Group 1 was significantly greater than that in Group 2 (p = 0.032).

PMOWHTO has favourable clinical and radiological outcomes and prevents PTS increase in simultaneous MMPRT repair and varus medial knee osteoarthritis patients without concomitant root tear.

Level IV, case series.

Background/Objectives: After open-wedge high tibial osteotomy (OWHTO), the patella is displaced distally, causing patellofemoral joint degeneration. The objective of this study was to ascertain whether the combination of OWHTO and lateral retinacular release (LRR) can prevent articular cartilage degeneration of the patellofemoral joint using magnetic resonance imaging T2 mapping. Methods: This study included 37 patients (37 knees) who underwent OWHTO alone (OWHTO group) and 37 patients (37 knees) who underwent OWHTO with LRR (OWHTO + LRR group) with a correction angle of <10° for varus knee osteoarthritis. MRI was performed on all knees prior to and 6 months after surgery to assess the patellar cartilage in sagittal images for T2 mapping. Three regions of interest, (the medial facet, patellar ridge, and lateral facet), were established for the articular cartilage on the patellar side. The T2 values were subsequently quantified. Lower limb alignment, patellar height, patellar tilt angle, and lateral shift ratio were evaluated pre-and post-surgery. Results: Mean T2 values at 6 months post-surgery of the medial facet and patellar ridge of the OWHTO group showed a significant increase after surgery; no significant changes were observed in either region in the OWHTO + LRR group. In both groups, a significant decrease in patellar tilt angle was observed postoperatively; no change was noted in the lateral shift ratio or congruence angle. The change in patellar tilt angle was significantly lower in the OWHTO + LRR group than in the OWHTO group. Conclusions: LRR combined with OWHTO prevented patellofemoral joint cartilage degeneration after surgery in cases of varus knee osteoarthritis.

Anterior knee pain and other patello-femoral (PF) complications frequently limit the success of total knee arthroplasty as the final treatment of end stage osteoarthritis. However, knowledge about the in-vivo loading conditions at the PF joint remains limited, as no direct measurements are available. We hypothesised that the external knee flexion moment (EFM) is highly predictive of the PF contact forces during activities with substantial flexion of the loaded knee.

Six patients (65-80 years, 67-101 kg) with total knee arthroplasty (TKA) performed two activities of daily living: sit-stand-sit and squat. Tibio-femoral (TF) contact forces were measured in vivo using instrumented tibial components, while synchronously internal TF and PF kinematics were captured with mobile fluoroscopy. The measurements were used to compute PF contact forces using patient specific musculoskeletal models. The relationship between the EFM and the PF contact force was quantified using linear regression.

Mean peak TF contact forces of 1.97-3.24 times body weight (BW) were found while peak PF forces reached 1.75 to 3.29 times body weight (BW). The peak EFM ranged from 3.2 to 5.9 %BW times body height, and was a good predictor of the PF contact force (R 2 = 0.95 and 0.88 for sit-stand-sit and squat, respectively).

The novel combination of in vivo TF contact forces and internal patellar kinematics enabled a reliable assessment of PF contact forces. The results of the regression analysis suggest that PF forces can be estimated based solely on the EFM from quantitative gait analysis. Our study also demonstrates the relevance of PF contact forces, which reach magnitudes similar to TF forces during activities of daily living.

Tibial rotational deformity is a known risk factor for patellofemoral joint (PFJ) disorders. However, it is commonly associated with other abnormalities which affect the PFJ. The purpose of this study was to describe the prevalence of associated factors known to affect PFJ in patients undergoing rotational tibial osteotomy and their implication for the correction level.

All patients with PFJ disorder, who underwent rotational tibial osteotomy between July 2009 and February 2020, were included. Patients were excluded if there were no preoperative computed tomography (CT)/magnetic resonance imaging (MRI). Scans were analyzed by 2 observers. Parameters of interest were femoral version, tibial torsion, trochlear dysplasia, lateral trochlear inclination (LTI), tibial tuberosity-trochlear groove (TT-TG) distance, Insall-Salvati (IS), and Caton Deschamps Index (CDI).

The search resulted in 80 knees, which had a mean femoral version of 21.0 ± 11.7, tibial torsion of 45.9 ± 9.1, TT-TG of 18.3 ± 5.5, and LTI of 11.4 ± 14.7. In total, 42.5% had TT-TG value of ≥ 20 mm. Patella alta/baja was found in 54% based on CDI or IS >1.2 and <0.8. High-grade trochlear dysplasia was found in 25%. In total, 29% had a tibial torsion abnormality but normal TT-TG and patella height. In total, 18% had abnormal TT-TG but normal patellar height.

Based on the associated abnormalities of patella height and tubercle lateralization, 18% of the population were suitable for supratubercle osteotomy, and 29% of patients were suitable for diaphyseal or distal tibial osteotomy. A tibial tubercle osteotomy was required in 54% of patients, making a through-tubercle approach the most appropriate option for most patients.

Radiological cross-sectional study.

Despite advancements in prosthetic designs and surgical techniques, patellar dislocation remains a rare but significant complication following total knee arthroplasty, with an incidence ranging between 0.15% and 0.5%. This condition often requires revision surgery to alleviate discomfort and restore joint function. Among the methods to address patellofemoral instability, medial patellofemoral ligament reconstruction has gained attention. In this case, we present the first report of using the synthetic Ligament Augmentation and Reconstruction System (LARS; Surgical Implants and Devices, Arc-sur-Tille, France) for medial patellofemoral ligament reconstruction following patellar dislocation after total knee arthroplasty, offering a novel approach to avoid donor site morbidity.

An 87-year-old man with no significant comorbidities underwent NexGen posterior-stabilized-total knee arthroplasty (Zimmer Biomet, Warsaw IN) for advanced osteoarthritis in his left knee. Three months postoperatively, he experienced a persistent giving-way sensation and swelling in the knee after a fall. Physical examination revealed patellar subluxation, confirmed by imaging studies. A computed tomography scan showed no malrotation of the femoral or tibial components. The patient was diagnosed with a medial patellar retinacular tear and medial patellofemoral ligament rupture. He underwent medial patellofemoral ligament reconstruction using a Ligament Augmentation and Reconstruction System (LARS; Surgical Implants and Devices, Arc-sur-Tille, France) synthetic ligament, and the medial retinaculum was repaired. After a year of follow-up, the patient reported satisfactory knee stability, with no recurrence of patellar dislocation.

This case demonstrates the successful use of a synthetic Ligament Augmentation and Reconstruction System for Medial patellofemoral ligament reconstruction in managing post-arthroplasty patellar dislocation. It offers a less invasive alternative to autograft harvesting, reducing donor site morbidity while providing effective stabilization of the extensor mechanism. This approach could have significant clinical implications, particularly for elderly patients with compromised bone healing capacity.

Our study aims to investigate if the ratios proposed by Insall-Salvati and Caton-Deschamps follow the theory of normal distribution levels in a healthy population. 434 skeletal mature, healthy knees were obtained from a CT-scan-based modelling system (SOMA). Patellae height ratios were measured using the Insall-Salvati ratio and the Caton-Deschamps index. The patella height ratios of the sample population were plotted on a quantile plot and diagnosed as patella alta, baja or normal using the original ratio definitions. The study population patella height values at the 95th, 98th and 5th centiles were identified and compared to those described as alta or baja by Insall-Salvati and Caton-Deschamps. This meant that if the patient had patella alta, this would be defined as a ratio of ≥ 1.2 and hypothesised that this would align at the 98th centile of the study population, whilst if diagnosed as patella baja (≤ 0.74), this should align at the 5th centile of the population. The inter-rater reliability of both ratios was calculated using kappa statistics. Two authors made all calculations and compared them for consistency using the intraclass correlation coefficient. For the Insall-Salvati ratio, the study population's value at the 98th centile was equivalent to what Insall-Salvati describes as alta, a ratio of ≥ 1.2. In the study population, patients are overdiagnosed if using the Insall-Salvati ratio as patella baja ≤ 0.74, as the value at the 5th centile in the study population was 0.59. Using the Caton-Deschamps index, the 95th centile was 1.3, higher than the patella alta ratio determined by Caton as a ratio ≥ 1.2. Using Caton-Deschamps, patients are being underdiagnosed if utilising a patella baja ratio of ≤ 0.6. In our population, the 5th centile was 0.75. The two ratios had a kappa coefficient of 0.01, which indicates poor inter-rater reliability. Depending on the ratio used, caton-Deschamps and Insall-Salvati ratios diagnose patients as alta or baja differently. The current patella height ratios have originated from very small, select population samples. The future of patella height discussion should begin with data representing large populations. Then, we can discuss the upper and lower limits of abnormality.

To propose a reliable and standard 3D assessment method to analyze the effect of weight-bearing (WB) status on the location of patella and clarify the diagnostic performance of 3D parameters for recurrent patellar dislocation (RPD) in WB and non-weight-bearing (NWB) conditions.

Sixty-five knees of RPD patients and 99 knees of controls were included. Eight landmarks, two lines and a coordinate system were defined on 3D bone models of knees based on weight-bearing CT and non-weight-bearing CT. The shift and tilt of patella in three orthogonal axes (Xshift, Yshift, Zshift, Xtilt, Ytilt, Ztilt) were evaluated.

Xshift and Yshift were significantly higher, Zshift, Xtilt and Ytilt were significantly lower in WB condition than NWB condition (p < 0.001, p < 0.001, p = 0.001, p = 0.002, p = 0.010). In both WB and NWB conditions, Xshift, Yshift and Ztilt were significantly higher, and Xtilt was significantly lower in the RPD group than the control group (WB/NWB: p < 0.001/p = 0.002, p < 0.001/p = 0.001, p < 0.001/p < 0.001, p < 0.001/p = 0.009). In WB condition, Zshift and Ytilt were significantly higher in the RPD group than the control group (p = 0.011, p < 0.001). Ztilt had the best diagnostic performance for RPD in both WB and NWB conditions, with AUC of 0.887 (95% CI: 0.828, 0.946) and 0.885 (95% CI: 0.822, 0.947), respectively.

The 3D measurement method reliably and comprehensively reflected the relative spatial position relationship of the patellofemoral joint. It can be applied to the 3D preoperative planning of patellofemoral procedures. In addition, patellofemoral evaluation under the WB condition was essential to detect subtle underlying risk factors for RPD, with axial lateral patellar tilt being the best predictor.

This 3D measurement method under weight-bearing conditions contributes to comprehensively describing the relative spatial position of the patellofemoral joint in a standardized way and can be applied to preoperative evaluation for recurrent patellar dislocation.

Patellofemoral alignment is a 3D problem, and the accuracy of 2D parameters has been questioned. 3D measurement was reliable and comprehensively reflected relative spatial relationships of the patellofemoral joint. 3D measurements under weight-bearing condition help preoperative evaluation for RPD.

The incidence of anterior cruciate ligament (ACL) injuries in skeletally immature patients has drastically increased over the last decades. Morphology of the knee might play an important role. This literature review provides a systematic overview of knee morphological factors relevant to ACL injury in skeletally immature patients. The hypothesis of the present study is that multiple knee morphological parameters-such as a steep medial and lateral tibial slope (MTS and LTS) and a narrow intercondylar notch-can be identified as potentially relevant factors for ACL injury in this population.

Systematic review according to PRISMA guidelines. MEDLINE, Embase and Cochrane were searched in December 2023 for studies reporting on knee morphology and ACL injury in skeletally immatures. The following inclusion criteria were used: English/Dutch studies, full-text available, human studies and skeletally immature patients. Parameters with clinical homogeneity and presented in two or more studies as means with standard deviation were included in a meta-analysis using RevMan. Parameters that could not be included in the meta-analyses were presented in a descriptive manner.

After screening 1825 studies, a total of 18 studies were included, of which 16 studies had parameters included in the meta-analyses. These studies investigated 31 knee morphological factors for ACL injury in skeletally immatures. Meta-analyses identified a smaller notch width index (NWI) (0.25 vs. 0.26, mean difference: -0.02 95% confidence interval [CI]: -0.03 to -0.01, p ≤ 0.00001) steeper MTS and LTS (4.8° vs. 3.6° (mean difference: 0.55° 95% CI: 0.09-1.01, p = 0.02) and 4.3° vs 2.8° (mean difference: 2.04° 95% CI: 0.75-3.32, p = 0.0003), respectively) and higher LTS/MTS ratio as risk factors for ACL injury in skeletally immature patients.

A small NWI, steeper MTS and LTS and higher LTS/MTS ratios were identified as relevant knee morphological factors for ACL injuries in skeletally immature patients.

Level III.

To identify risk factors for complete medial patello-femoral ligament (MPFL) rupture after first lateral patellar dislocation (LPD) and to develop a model to predict the risk of rupture.

Patients who presented with first LPD between February 2019 and June 2024 and were diagnosed with complete MPFL rupture on magnetic resonance imaging (MRI) were retrospectively reviewed. Patients with normal MRI findings in a 1:1 ratio were selected as the control group by computer-assisted randomisation.All patients in both groups were asked to perform MRI on, tibial tuberosity-trochlear groove (TT-TG) distance, lateral trochlear inclination (LTI) angle, sulcus angle (SA), medial femoral condyle height (MFCH), lateral femoral condyle height (LFCH), trochlear height (TH), patellotrochlear index (PTI), Koshino-Sugimoto Index (KSI), Caton-Deschamps Index (CDI) and Insall-Salvati Index (ISI) were measured and recorded. All measurements were made by two different orthopaedists and intra-observer reliability was evaluated. The measurements between the groups were compared statistically.

A total of 98 patients, including 49 patients with complete MPFL rupture (study group) and 49 patients in the control group, were included in the study. Thirty of the patients in both groups were males and 19 were females. Mean age was 23.55 years in the study group and 24.29 years in the control group (p = 0.447). Satisfactory ICC scores were obtained in all measurements. LTI was lower in the study group than in the control group (p = 0.002), while SA was higher in the study group than in the control group. Both CDI and ISI were statistically significantly higher in the study group compared to the control group (p = 0.002, p = 0.003). The probability of predicting the risk of complete MPFL rupture of the risk analysis model created with radiological risk factors for complete MPFL rupture was 70.4%.

LTI, SA, TH and patella alta are risk factors for complete MPFL rupture after first LPD. Risk analysis of complete MPFL rupture after first dislocation can be successfully performed with MRI findings. This risk analysis can be used to predict the risk of developing complete MPFL after primary LPD, especially in risky patient groups, and can be used in a simple way to decide which patients will receive a preventive programme without the need for additional examination.

Level III, case-control study.

Pseudo-patella baja (PPB) was one of the complications after total knee arthroplasty (TKA). This complication may be closely related to the occurrence of knee joint movement limitation and pain after TKA. This study aimed to investigate whether PPB affects clinical outcomes after TKA and to study the biomechanical effects of PPB after TKA.

This study was a retrospective case series of 462 eligible patients (563 knees). Clinical evaluation was performed using the visual analogue scale (VAS), the Hospital for Special Surgery (HSS), the Western Ontario McMaster University Osteoarthritis Index (WOMAC) scoring systems, the 5-Level EuroQol Generic Health Index (EQ-5D-5L), the Forgotten Joint Score-12 (FJS-12), and patient satisfaction. CT and MRI scans of two healthy left knees and TKA prostheses were taken; 3D models including PPB, True patella baja (TPB), normal patella, and patella alta (PA) were created in FEA and applied load along the direction of quadriceps femoris. T-test, Mann-Whitney U-test, chi-squared (χ 2) test, and analysis of variance (ANOVA) were performed using GraphPad Prism (Version 8, GraphPad Software, USA). A statistically significant difference was considered at p < 0.05 with bilateral α.

The VAS, HSS, WOMAC, EQ-5D-5L, FJS-12, and patient satisfaction scores in the PPB and TPB groups were significantly worse than those in the patella normal (PN) group (p < 0.05). The PPB group found a positive correlation between Blackburne-Peel index (BPI) and FJS-12 score. PPB showed lower contact stress of patellofemoral joint compared to TPB when knee flexion was less than < 90° (p < 0.01), but no significant difference when flexion was more than > 90° (p > 0.05) in the finite element model with Patella baja (PB). The contact area of the patellofemoral joint tended to increase with the deepening of knee flexion, and decreased after reaching the peak value. The contact area of the patellofemoral joint tended to decrease with the increase in patellar height. There was no significant difference in the contact area of the patellofemoral joint among different patellar heights and different degrees of knee flexion (p > 0.05).

PPB after TKA may increase patellofemoral joint stress and postoperative complications like anterior knee pain.

Sulcus-deepening trochleoplasty (TP) effectively treats patellofemoral (PF) instability (PFI) caused by high-grade trochlear dysplasia (TD), but current evidence is based on small case series. We hypothesised, that TP would result in significant functional improvements and a low re-dislocation rate but would not accelerate the progression of PF cartilage deterioration.

We retrospectively reviewed all TP cases performed by a single surgeon between 2015 and 2021. Inclusion criteria were postoperative Magnetic resonance imaging (MRI) >6 and >12 months and a clinical follow-up >12 months. Patients with simultaneous cartilage repair, open physes or incomplete records were excluded. Clinical outcomes were assessed using pre- and postoperative scores, postoperative Banff Patellofemoral Instability Instrument (BPII) 2.0 and Knee Injury and Osteoarthritis Outcome Score (KOOS), re-dislocation rate and patient satisfaction. PF cartilage was evaluated via Area Measurement and Depth & Underlying Structures (AMADEUS) scores preoperatively, at 6 months and at the final follow-up.

We included 113 patients (25.8 ± 8.3 years) with high-grade TD (Dejour B-D; mean lateral inclination angle: -2.9 ± 9.1°), 85% of whom had advanced cartilage lesions. All underwent TP, lateral retinacular lengthening (LRL) and medial patellofemoral ligament reconstruction (MPFL-R). After 34.8 ± 20.9 months, function, pain levels and Tegner scores improved significantly (p < 0.001). KOOS dimensions were: symptoms 79.9 ± 13.5, pain 86.4 ± 12.1, activity 91.9 ± 8.3, sports 71.7 ± 22.2 and quality-of-life 58.1 ± 23.8. BPII 2.0 was 64.3 ± 31.4. Preoperative AMADEUS scores (55.2 ± 17.4) remained stable at 6 months (p = 0.343) but improved to 58.4 ± 16.0 at 28.6 (12-89) months (p = 0.004). Complication and re-dislocation rates were 5.3% and 1.8%, with 93% patient satisfaction.

Sulcus-deepening TP with MPFL-R and LRL yields good to excellent short-term results without progressive chondral deterioration, enabling patients to return to their prior or higher activity levels despite advanced preoperative chondral lesions. TP can be considered a safe, joint-preserving technique for PF stabilisation.

Level III, retrospective cohort study.

Patellofemoral joint (PFJ) diseases are chronic degenerative conditions that contribute to knee joint symptoms. Unicompartmental knee arthroplasty (UKA) is widely regarded as an effective treatment for knee osteoarthritis (KOA); however, its specific indications remain a subject of debate.

Patients with PFJ disease are expected to experience outcomes post-UKA comparable to those of patients without PFJ disease.

We conducted this meta-analysis following the guidelines outlined by the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). A comprehensive search of PubMed, Embase, and Web of Science databases was conducted for studies examining the association between PFJ disease and UKA, including publications up to September 2024. Extracted data encompassed author, publication year, country, disease type, prosthesis type, sample size, mean patient age, gender distribution, follow-up duration, PFJ disease prevalence at surgery, diagnostic methods, and whether PFJ disease was considered a contraindication for UKA. To maintain objectivity, only studies in which PFJ diseases were visually identifiable were included in the meta-analysis. Statistical analyses were performed using Stata 15.0 and Review Manager 5.4.1. A random-effects meta-analysis was conducted to evaluate the Oxford Knee Score (OKS), Knee Society Score (KSS), flexion range of motion (ROM), Forgotten Joint Score (FJS), Tegner activity score, and prosthesis survival rate, with outcomes stratified by PFJ disease type (PFJ degeneration or patella cartilage injury). Mean differences, confidence intervals, and P values were calculated for comparisons between the PFJ disease and non-PFJ disease groups. The Methodological Index for Non-Randomized Studies (MINORS) criteria and the Newcastle-Ottawa Scale (NOS) were applied to evaluate the risk of bias. To address heterogeneity, sensitivity analyses were performed, and publication bias was assessed using funnel plots and Egger's test.

A total of 14,866 knees from 48 relevant studies were included in this systematic review. Methodological quality was assessed using the MINORS criteria, with case series scoring 11.0/16 and cohort studies scoring 18.2/24. PFJ degeneration emerged as the most studied condition, followed by patella cartilage injury. Clinical outcomes assessments indicated that medial PFJ degeneration, anterior knee pain, patella cartilage damage, and patella baja did not significantly impact UKA outcomes or prosthesis survival. However, severe lateral PFJ degeneration, lateral patellar subluxation, lateral trochlear osteophytes, and patellar bone marrow edema did influence results. Fifteen high-quality studies were included in the meta-analysis, involving 6080 patients-1338 in the PFJ disease group and 4,742 in the non-PFJ disease group. With an average NOS score of 7.2, the studies were generally of high quality. Meta-analysis results showed no significant differences between groups in final follow-up OKS, FJS, Tegner activity score, or prosthesis survival rate. However, the PFJ disease group had lower KSS and reduced flexion ROM compared to the non-PFJ disease group. Subgroup analysis further revealed that the PFJ degeneration group scored lower than the patella cartilage injury group on OKS, KSS, and flexion ROM following UKA.

In summary, PFJ disease was found to have limited impact on UKA outcomes; however, caution is recommended for cases involving severe lateral PFJ degeneration due to potential restrictions in postoperative knee function, particularly affecting flexion ROM in UKA patients.

Patellar instability is a multifactorial pathology requiring precise evaluation of its contributing factors, particularly patella alta. Patellotibial height measurement indexes, such as the Caton-Deschamps index, have the disadvantage of being referenced to the tibia. Patellotrochlear indexes are more appropriate but fail to account for variable knee flexion during magnetic resonance imaging (MRI).

This study aims to validate a new MRI-based patellotrochlear measurement, the extension patellar engagement (EPE) index, which is reproducible and measures patellar height relative to the trochlea independently of knee flexion during MRI.

A retrospective study was conducted on 77 MRIs (37 unstable patients with a history of patellar dislocation, 40 controls with meniscal injury). The EPE index is the ratio between the patellar engagement length on the cartilaginous trochlea and the patellar cartilage length, measured on a knee virtually extended. Four measurements on multiple sagittal slices were used to calculate the EPE index.

The inteobserver intraclass correlation coefficient (ICC) was excellent (0.79). The mean EPE index's value for all knees was 0.22. It was significantly higher (p = 0.034) in the instability group (0.26) compared to the control group (0.19). The average knee flexion during MRI was 11 ° (range: -8 ° to 25 °).

The EPE index is reproducible. It is an anatomical index to classify patella alta when the patella does not reach the trochlea in knee extension (EPE index ≤0). It is also a functional index, with a mean value of 0.19 in the control group.

The EPE index measures the patellar engagement on the trochlea taking into account the knee flexion during MRI. It may guide surgical decision-making for patellar distalization and quantify the required correction.

III; retrospective comparative study.

To evaluate the influence of patellar morphology on functional outcomes and patellofemoral joint alignment after unicompartmental knee arthroplasty (UKA).

This study retrospectively analyzed the clinical and imaging data of 207 patients with osteoarthritis of the unicompartment of the knee who underwent UKA between September 2020 and April 2023. Patients were divided into three groups according to the Wiberg classification: group W1 (I, n = 47), group W2 (II, n = 117), and group W3 (III, n = 43). Knee function was assessed using the Hospital for Specialty Surgery (HSS) knee score and Feller patellar score, and the incidence of anterior knee pain after surgery was recorded and compared. Imaging parameters such as patellar tilt angle (PTA), lateral patellofemoral angle (LPA) and Insall-Salvati ratio (ISR) were measured to assess patellofemoral joint alignment.

The HSS scores of the three groups were not statistically different; the postoperative Feller scores of the group W3 differed significantly from those of the other two groups. The incidence of early postoperative anterior knee pain was higher in the group W3 than in the other two groups. The difference between preoperative PTA, postoperative PTA and preoperative LPA in the group W3 and the other two groups was statistically significant.

Patients with Wiberg III patellae exhibited worse patellar scores, as well as more anterior knee pain and patellar tilt postoperatively. This finding highlights the need for individualized treatment to the Wiberg III patella during UKA to enhance surgical outcomes.

The purpose of this study was to compare postoperative patellar tilt at 4 months follow-up in a consecutive series of randomised patients that received individualised or off-the-shelf (OTS) primary total knee arthroplasty (TKA). The hypothesis was that patellar tilt would be lower and less variable in patients who received individualised TKA compared to patients who received OTS TKA.

A consecutive series of 385 patients randomised (1:1) to receive either OTS TKA or individualised TKA were analysed. Pre- and postoperative radiographs at 4 months were obtained of weight-bearing long leg, anterior-posterior and lateral knee views and a skyline view at 30° of flexion. Postoperative patellar tilt was measured between the anterior femoral line and patellar resection surface (β) and the anterior femoral line and mediolateral patellar axis (σ). Postoperative patellar tilt (absolute value) was compared between the individualised and OTS TKA groups based on preoperative phenotypes of their femoral mechanical angle, tibial mechanical angle and hip-knee-ankle angle. Variability in postoperative patellar tilt was compared using the 95% confidence intervals (CIs).

Comparisons of baseline patient characteristics revealed no difference between the individualised and OTS TKA groups. Comparison of absolute postoperative patellar tilt revealed significant differences between individualised and OTS TKA (|β|, 1.0° ± 1.0° and 2.5° ± 2.2°, respectively, p < 0.001; |σ|, 1.7° ± 1.6° and 2.8° ± 2.3°, respectively, p < 0.001). The 95% CI of postoperative patellar tilt (|β|) was narrower in patients that received individualised compared to OTS TKA (0.0° to 3.8° and 0.1° to 8.3°, respectively), irrespective of their preoperative phenotype.

Patients who underwent individualised TKA had lower and less variable postoperative patellar tilt than those with OTS TKA, irrespective of preoperative phenotype. Individualised TKA allows the decoupling of the tibiofemoral and patellofemoral joints, replicating anatomical trochlear orientation and improving patellar tilt, which could facilitate better clinical outcomes.

This study constitutes a part of a larger registered randomised controlled trial comparing patient satisfaction following OTS versus individualised TKA (NCT04460989).

Level II.

The correlation between the morphological structure of the patellofemoral joint (PFJ) and the severity of knee joint osteoarthritis (KOA) remains uncertain. This study aims to investigate the correlation between the severity of knee joint osteoarthritis and the alignment of patellofemoral and patellar height on radiographs.

This multi-center, retrospective study analyzed the magnetic resonance imaging (MRI) scans and anteroposterior radiographs of 534 adult outpatients with KOA. To evaluate the radiographic severity of KOA, anteroposterior radiographs of the knee and the Kellgren-Lawrence (K-L) grade were used. Knee MRI scans were used to measure the patellar length ratio (PLR), sulcus angle (SA), lateral patellar tilt angle (LPTA), and the distance between tibial tuberosity and trochlear groove (TT-TG). We examined the association between the configuration of the PFJ, arrangement, and harshness of the KOA. Information on participants' demographics, such as age, sex, side, height, and weight, was collected. A chi-squared test was used for the correlation of radiographic severity of KOA with sex and the affected side. Spearman correlation was used for patellofemoral alignment or morphology and the radiographic severity of lateral KOA. Multiple linear regression models were used for the association between LPTA, SA, TT-TG, and severity of KOA after accounting for demographic variables.

The study comprised of 534 patients; of these, 339 (63%) were female. A total of 586 knees were evaluated in this study. Age showed a strong positive correlation with KOA severity (r = 0.516, P <0.01), whereas LPTA showed a strong negative correlation (r = -0.662, P <0.01). Additionally, SA (r = 0.616, P <0.05), and TT-TG showed a strong positive correlation (r = 0.770, P <0.01) with tibiofemoral osteoarthritis (TFOA) severity. Multiple linear regression analysis indicated that knee osteoarthritis severity (β = -2.946, P <0.001) and side (β = -0.839, P = 0.001) was associated with LPTA; knee osteoarthritis severity (β = 5.032, P <0.001) and age (β = -0.095, P <0.001) was associated with SA; knee osteoarthritis severity (β = 2.445, P <0.001), sex (β = -0.326, P = 0.041), body mass index (β = -0.061, P = 0.017) and age (β = -0.025, P <0.001) was associated with TT-TG. The radiographic severity of KOA positively correlated with PLR, SA, and TT-TG, but negatively correlated with LPTA.

Radiographic severity of KOA was positively associated with age, SA, and TT-TG but negatively associated with LPTA.

To assess the outcomes of medial patellofemoral ligament (MPFL) reconstruction using synthetic suture tape in paediatric patients with patellofemoral instability (PFI).

This ambispective comparative study, conducted from 2014 to 2022, included paediatric patients who underwent MPFL reconstruction with synthetic suture tape and had a minimum follow-up of 1 year. Pre- and postoperative clinical and functional outcomes, patient satisfaction and complications were assessed.

The study comprised 22 patients (29 knees), with a median age at surgery of 14.4 years (interquartile range [IQR] 10.9-16.7) and a median follow-up of 46.5 months (24.7-66). Notably, 13 knees (44.8%) had open growth plates at the time of surgery. The cohort included patients with Down syndrome (3 patients), Ehlers-Danlos (2), arthrogryposis (1), generalized joint hypermobility (8) and previous unsuccessful PFI surgeries (8). Concomitant procedures were performed on 16 knees. Postoperatively, improvements were observed in all but one patient, who reported residual pain. There were two other complications: one suture-tape rupture and one surgical wound infection. Functional scores significantly improved: Kujala, +14 points (7-29) (p < 0.001); IKDC, +10.5 points (5.2-25.3) (p < 0.001); Tegner, +2 points (0-4) (p < 0.001); Lysholm, +15 points (0-37.5) (p < 0.001). Most patients achieved excellent outcomes by Crosby-Insall criteria (21 patients, 72.4%) and reported high satisfaction (23 patients, 79.3%).

MPFL reconstruction using synthetic suture tape is a viable and effective treatment for paediatric patients with PFI, particularly for those with connective tissue disorders, generalized joint hypermobility or past surgical failures, significantly enhancing clinical and functional outcomes with an acceptable complication rate.

Level IV.

To investigate whether the patellotrochlear index (PTI) predicts patella alta as determined by tibial-based methods of Insall-Salvati (IS) and Caton-Deschamp (CDI) indexes in a pathological population (with patellofemoral pain and/or instability), in addition to determining whether PTI and sagittal patellofemoral engagement (SPE) correlate with trochlea length as determined by lateral condyle index (LCI).

Patients with confirmed patella alta (IS/CDI ratio >1.2) undergoing tibial tubercle osteotomy for patellofemoral pain/instability with an available magnetic resonance imaging (MRI) scans were included. Patients who had undergone previous soft-tissue realignment, previous surgery, or trauma to the extensor mechanism were excluded. Two raters measured the IS, CDI, PTI, SPE, LCI, and knee flexion angle (KFA) on MRI. Interobserver reliability and correlation between measurements were calculated.

In total, 71 knees were included. PTI (0.73), SPE (0.836), LCI (0.701), and KFA (0.8) demonstrated good- to near-excellent interobserver reliability. IS (0.65) and CDI (0.66) demonstrated moderate interobserver reliability. PTI and SPE showed the strongest significant correlation (0.8112, P = 2.2 × 10-16). IS and CD (0.39, P = .0007) showed a moderate significant correlation. PTI and KFA (0.53, P = 1.685 × 10-6) and SPE and KFA (0.61, P = 1.991 × 10-8) had a significant moderate correlation. LCI and KFA (-0.37, P = .0017) showed a significant moderate negative correlation. All other measurement indices correlated poorly and were insignificant. A total of 94.4% of the knees were defined as having patella alta using IS, with the remaining 5.6% having a raised CDI. Only 14% of cases had an IS of >1.2, a CDI >1.2, and a PTI <0.125, which increased to 39% (28/71) when the threshold for PTI was increased to <0.28.

There was no correlation between tibial (IS and CD) and femoral methods (PTI and SPE) of quantifying patella alta. PTI and SPE did not correlate with trochlea length as measured by LCI. PTI, SPE, and LCI are significantly affected by the KFA during MRI.

Level IV, retrospective diagnostic radiographic investigation.

Medial open-wedge high tibial osteotomy (OWHTO) is performed for isolated medial compartment osteoarthritis or osteonecrosis of the knee and correction of varus deformity of the full lower extremity. OWHTO may induce sagittal parameter changes, including these in the tibial posterior slope (TPS), patellar height (PH), and patellofemoral joint problems. This study aimed to identify radiographic parameters associated with patellofemoral cartilage damage after OWHTO.

The patellofemoral joint cartilage worsens after OWHTO and is adversely affected by PH changes.

Twenty patients (25 knees) who underwent primary OWHTO and subsequent implant removal surgery, including second-look arthroscopy for evaluation of the patellofemoral cartilage condition were enrolled. The patients were received 12 to 35 months of postoperative follow-up, and categorized into two groups according to whether patellofemoral cartilage damage worsened. TPS and PH parameters, including the Insall-Salvati, Blackburne-Peel, Caton-Deschamps, and modified Blumensaat (MBI) indices, were measured on lateral knee radiographs. The hip-knee-ankle and medial proximal tibial angles were measured using an anteroposterior radiograph of the full lower extremity. The extent of change from preoperative to postoperative (Δ) was calculated for all indices.

Eleven knees (44%) had worsening cartilage conditions in the femoral trochlear groove, with>1-degree of deterioration in the International Cartilage Repair Society grade. The radiographic measure for predicting patellofemoral cartilage deterioration was ΔMBI (95% confidence interval [CI]: 3.53×10-14-0.812, p=0.047). PF cartilage damage tended to progress in ΔMBI<-0.145. The postoperative TPS and HKAA in patients with deterioration in patellofemoral cartilage damage was greater than that in patients without deterioration in patellofemoral cartilage damage (p=0.037 and 0.038, respectively).

The patellofemoral cartilage damage tends to progress after OWHTO. ΔMBI is a factor for predicting worsening patellofemoral cartilage condition. However, attention should be paid to the excessive posterior slope as high TPS and valgus alignment as valgus HKAA because intraoperative control of MBI is impossible.

IV, retrospective study.

Available conventional tibial tubercle lateralization (TTL) parameters fail to account for individual patient size or anatomy.

To evaluate the predictive ability of individualized TTL parameters and clarify the best predictor of patellar dislocation (PD) and to determine the relationship of the best predictor with other risk factors of PD with quadriceps isotonic contraction.

Cohort study (diagnosis); Level of evidence, 2.

A total of 15 patients with PD (28 knees) and 14 controls (28 knees) underwent 4-dimensional computed tomography, and the image with the knee fully extended and quadriceps isotonically contracted was selected for evaluation. The following TTL parameters were measured on the images: tibial tubercle-trochlear groove (TT-TG) distance, tibial tubercle-Roman arch distance, and tibial tubercle-posterior cruciate ligament distance, as well as their ratios to femoral condylar width and patellar width (PW). In addition, the following parameters were measured: Insall-Salvati ratio, Blackburne-Peel ratio, Caton-Deschamps ratio, modified Insall-Salvati ratio, bisect offset index, congruence angle, lateral patellar tilt, lateral trochlear inclination, sulcus depth, sulcus angle, trochlear groove medialization, patella-patellar tendon angle, patellofemoral axis angle (P-FAA), patellar articular facet-patellar tendon angle, patellar articular facet-femoral axis angle (PA-FAA), and patellar shape according to Wiberg type. The area under the receiver operating characteristic curve (AUC) was calculated to access the diagnostic accuracy of the TTL parameters for PD, and the TTL parameters with high diagnostic ability were evaluated for correlation with the remaining parameters.

The TT-TG/PW ratio had the best diagnostic ability for PD (AUC = 0.890). The TT-TG/PW ratio was positively correlated with bisect offset index, congruence angle, lateral patellar tilt, P-FAA and PA-FAA (r = 0.610, 0.465, 0.635, 0.553 and 0.418, respectively; P≤ .027 for all), and TT-TG/PW ratio was greater in knees with type II versus type III patella (P = .017).

With the knee fully extended and quadriceps isotonically contracted, the TT-TG/PW ratio was found to be the best predictor of PD and reflected individualized TTL, which helps with clinical preoperative planning.

Patellar height changes after tibial tubercle osteotomy (TTO) have not yet been described. We aimed to evaluate whether TTO ± medial patellofemoral ligament reconstruction (MPFL-R) influences patellar height and tendon length, hypothesizing that TTO would decrease patellar height and tendon length.

A retrospective review was performed of skeletally mature adolescents (<18 y) receiving primary anteromedialization or medialization TTO ± MPFL-R. Patients with at least 6 months of radiographic follow-up were included in the study. Pre and postoperative patellar heights were assessed on lateral, weight-bearing, and flexion (30 to 70 degrees) radiographs using the Blackburne-Peel Index (BPI), Caton-Deschamps Index (CDI), and Insall-Salvati Ratio (ISR). Subgroup analyses were performed to compare patellar height changes in patients with preoperative patella alta, norma, and baja, as well as between patients undergoing medialization and anteromedialization TTO. Data were analyzed for normality using a Shapiro-Wilk test, and paired-sample t tests were performed.

Forty-nine knees were included (mean age: 15 y; range: 12 to 17). A significant decrease in mean patellar height after TTO ± MPFL-R was observed across all measures: BPI (0.12, P = 0.000783), CDI (0.08, P = 0.01062), and ISR (0.15, P = 0.00000075). Patellar tendon length decreased by 2.26 mm ( P = 0.001272). Subgroup analyses demonstrated a decrease in mean patellar height across all 3 measurements ( P < 0.001; BPI, CDI, and ISR) for patients with preoperative patella alta but not patella norma or baja. Additional subgroup analysis showed a patellar height decrease using BPI (0.15, P = 0.004583) and ISR (0.14, P = 0.0002806) for patients receiving medialization TTO but not anteromedialization. The anteromedialization cohort did not demonstrate patellar height change using BPI and CDI; ISR demonstrated a decrease (0.10, P = 0.00917).

Mean patellar height and tendon length decreases after TTO ± MPFL-R in skeletally mature, adolescent patients. Subgroup analyses suggest these changes occur in patients with preoperative patella alta and/or patients who undergo medialization TTO. These data suggest that some distalization in patellar positioning may be achieved without formal distalization osteotomy.

The US Food and Drug Administration approved matrix-induced autologous chondrocyte implantation (MACI) for use in the United States in 2016, and it has proven to be an effective treatment for articular cartilage defects in the knee. Concomitant patellar stabilization and realignment procedures, such as tibial tubercle osteotomy (TTO) and medial patellofemoral ligament (MPFL) reconstruction, are often performed with MACI to prevent further damage to the knee and to sustain the integrity of the cartilage repair. This Technical Note aims to describe MACI in the patella with concomitant patellar stabilization and realignment and to provide a treatment algorithm for when various simultaneous procedures are indicated. The authors believe that correction of patellar malalignment and instability is crucial to the success of cartilage repair procedures. Therefore, we recommend that TTO and MPFL reconstruction be performed with MACI procedures of the patella when the anatomic pathology and pertinent patient history, such as articular cartilage defects with patellar instability and abnormal patellar alignment, are present.

To develop and validate a deep learning-based approach to automatically measure the patellofemoral instability (PFI) indices related to patellar height and trochlear dysplasia in knee magnetic resonance imaging (MRI) scans.

A total of 763 knee MRI slices from 95 patients were included in the study, and 3393 anatomical landmarks were annotated for measuring sulcus angle (SA), trochlear facet asymmetry (TFA), trochlear groove depth (TGD) and lateral trochlear inclination (LTI) to assess trochlear dysplasia, and Insall-Salvati index (ISI), modified Insall-Salvati index (MISI), Caton Deschamps index (CDI) and patellotrochlear index (PTI) to assess patellar height. A U-Net based network was implemented to predict the landmarks' locations. The successful detection rate (SDR) and the mean absolute error (MAE) evaluation metrics were used to evaluate the performance of the network. The intraclass correlation coefficient (ICC) was also used to evaluate the reliability of the proposed framework to measure the mentioned PFI indices.

The developed models achieved good accuracy in predicting the landmarks' locations, with a maximum value for the MAE of 1.38 ± 0.76 mm. The results show that LTI, TGD, ISI, CDI and PTI can be measured with excellent reliability (ICC > 0.9), and SA, TFA and MISI can be measured with good reliability (ICC > 0.75), with the proposed framework.

This study proposes a reliable approach with promising applicability for automatic patellar height and trochlear dysplasia assessment, assisting the radiologists in their clinical practice.

The objective knee landmarks detection on MRI images provided by artificial intelligence may improve the reproducibility and reliability of the imaging evaluation of trochlear anatomy and patellar height, assisting radiologists in their clinical practice in the patellofemoral instability assessment.

• Imaging evaluation of patellofemoral instability is subjective and vulnerable to substantial intra and interobserver variability. • Patellar height and trochlear dysplasia are reliably assessed in MRI by means of artificial intelligence (AI). • The developed AI framework provides an objective evaluation of patellar height and trochlear dysplasia enhancing the clinical practice of the radiologists.

This study aims to quantitatively assess the relationship between the patella alignment and morphology and knee osteoarthritis (KOA), as well as the kinematics and kinetics of the knee, using gait analysis.

Eighty age-matched patients with KOA and control subjects were evaluated. Incident radiographic osteoarthritis (iROA) was identified using a Kellgren-Lawrence (KL) grade of ≥ 2. The modified Insall-Salvati ratio (Mod-ISR), patellar tilt angle (PTA), and patella index (PI) were utilized to evaluate the sagittal and transverse alignment of the patella and its morphology, respectively. Regression analyses were conducted to explore associations between patellar measurements and KOA, iROA, kinematics, and kinetics.

Significant differences were observed between the control and KOA groups in terms of KL grade, patella alta, abduction angle, and reaction force to the ground (P < 0.05, respectively). Following adjustment for covariates, a significant positive association was found between patella alta and KOA (OR = 0.307, 95%CI: 0.103 to 0.918, P = 0.035). Additionally, a significant negative association was observed between PTA and abduction angle (B = -0.376, 95%CI: -0.751 to -0.002; P = 0.049). The PI exhibited a statistically significant association with log-transformed vertical ground reaction force (B = 0.002, 95%CI: 0.001 to 0.003, P = 0.002). Furthermore, adjustment for covariates did not reveal any significant correlations with other indicators (P > 0.05, respectively).

This study provides further evidence that proper alignment and morphology of the patella might be associated with maintaining normal biomechanical function. In addition, intervention measures targeting relevant patellar parameters, such as Mod-ISR, PTA, and PI, may positively impact KOA treatment outcomes.

Abnormal patellar height has been identified as a source of aberrant mechanical functioning within the patellofemoral joint. The purpose of this study is to examine the statistical agreement among three commonly used classification methods: Blackburne-Peel (BPI), Caton-Deschamps (CDI) and Insall-Salvati (ISR), by evaluating (1) the rates of patella alta identification and (2) the ability for one index to predict another.

One hundred lateral knee radiographs were evaluated using BPI, CDI and ISR to classify each knee as patella normal, patella alta or patella baja. Linear regression analysis was performed to evaluate the relationship between each index. Conversion equations were then derived using the reported linear regression best-fit line, comparing each pair of indices.

Patella alta was identified in 15 knees using BPI, 15 using CDI and 25 using ISR. A total of seven knees were classified as patella alta by all BPI, CDI and ISR. Statistical analysis revealed significant correlation (p ≤ 0.001) among BPI and CDI (R2 = 0.706), BPI and ISR (R2 = 0.328) and CDI and ISR (R2 = 0.288). Wilcoxon Signed-Rank test between the three indices revealed no significant difference between the means of converted and original indices.

Despite their significant correlations and adequate reproducibility, variability between common patellar height indices render predictions and conversions between BPI, CDI and ISR inequivalent. Users of these indices must be aware of their incongruent properties when considering application to patients in the clinical setting. Furthermore, it remains unclear which patellar height measurement technique is the correct index to use in a given knee. This study highlights the need for further investigation to create a reliable and standardised method for identifying patella height.

Level IV.

Patella baja is a known complication of total knee arthroplasty (TKA). There is a limited understanding of the association between patellar resurfacing and the incidence of patella baja. We aimed to compare rates of patella baja between unresurfaced and resurfaced patellas in patients undergoing TKA.

A retrospective review of patients who underwent TKA between October 2009 and January 2020 was performed. Patients were included if they had at least one preoperative radiograph and a 1-year follow-up radiograph. Blackburne-Peel index (BPI) and Insall-Salvati ratios (ISRs) were measured on preoperative and 1-year postoperative radiographs and were used to define patella baja vs pseudopatella baja. Statistical analysis was performed using a linear model analysis of variance and the Fisher's exact test.

Three hundred eighteen TKAs were included, with 176 being resurfaced and 142 unresurfaced patellas. Of the resurfaced group, 4% (7/176) had true patella baja, compared to 5.6% (8/142) of the unresurfaced patellas. Of the resurfaced patellas, 8% (14/176) had pseudopatella baja, compared to 7% (10/142) in the unresurfaced group. Patellar resurfacing was not associated with a higher incidence of patella baja (P = .60) or pseudopatella baja (P = .83). Lower preoperative ISRs (P = .04) and BPIs (0.03) were highly predictive of a higher incidence of patella baja post-TKA.

Patellar resurfacing in TKA is not associated with a higher incidence of patella baja in TKA when compared to unresurfaced patellas. Lower preoperative ISRs and BPIs are highly predictive of a higher incidence of postoperative patella baja.

Patella alta is a clinical condition where the patella is positioned too proximal in relation to the femoral trochlea. Such an abnormality may cause patellar instability and predispose to recurrent patellofemoral dislocations and patellofemoral pain. There are no conclusive guidelines for determining a threshold for too high positioned patella, as several different methods have been described to measure patellar height. As a surgical solution, distalising tibial tubercle osteotomy has been described to correct excessive patellar height. In the early phase of the distalising tibial tubercle osteotomy postoperative protocol, weightbearing and knee flexion are limited with a brace commonly for 4-8 weeks to avoid potential implant failure leading to displacement of the osteotomy or non-union. The potential risks for adverse effects associated with the limitation rehabilitation protocol include a delay in regaining knee range of motion, stiffness and muscle weakness. As a result, recovery from surgery is delayed and may lead to additional procedures and long-term morbidity in knee function. This is a prospective, randomised, controlled, single-blinded, single centre trial comparing a novel accelerated rehabilitation protocol with the traditional, motion restricting rehabilitation protocol. All skeletally mature patients aged 35 years and younger, referred to as the distalising tibial tubercle osteotomy procedure group, are eligible for inclusion in the study. Patients will be randomised to either the fast rehabilitation group or the traditional rehabilitation group. Patients with patellar instability will be additionally treated with medial patellofemoral ligament reconstruction. The hypothesis of the trial is that the novel accelerated rehabilitation protocol will lead to faster recovery and improved functional outcome at 6, 12 and 24 weeks compared with the conservative rehabilitation protocol. A secondary hypothesis is that the complication rate will be similar in both groups. The study will document short-term recovery and the planned follow-up will be 3 years. After the 1-year follow-up, the trial results will be disseminated in a major peer-reviewed orthopaedic publication. Protocol version 3.6, date 28/11/2023.

The radiographical assessment of patella height has historically been performed using X-Ray. The aim of this study was to evaluate a new method for the assessment of patella height using MRI and to assess the correlation with the X-Ray based assessment.

159 patients who had both lateral radiographs and MRI images were included. Parameters measured included traditional radiographical CDI, MRI-based CDI, and TT-TG distance. On the basis of the TT-TG, the patients were divided into 2 groups. Two different methods were used to assess CDI using MRI: using a single slice image, and an alternative technique using two different cross-sectional images. The correlation of the two measurement methods was assessed using Pearson's correlation coefficient. The intraclass correlation coefficient (ICC) was determined from the measurements of the two investigators.

The average TT-TG distance was 11.6 mm (± 4.6). In patients with a TT-TG < 15 mm, both measurement methods showed comparable correlation with measurements on X-Ray. In patients with a TT-TG of > 15 the the new cross-sectional imaging method showed higher correlation with traditional X-Ray assessment compared to CDI assessment using the traditional single slice method (r = 0.594, p < 0.001 vs. r = 0.302, p = 0.055).

The assessment of CDI on MRI using a cross-sectional imaging method has a better correlation with traditional X-Ray assessment of CDI than single-slice assessment. This is particularly true in patients with elevated TT-TG and as such should be preferentially used in the assessment of Patellar height in this cohort.

Total patellectomy is currently reserved for exceptional cases, such as recalcitrant patellofemoral instability and comminuted fractures, due to its demonstrated negative impact on knee biomechanics. Therefore, managing patellectomy is crucial to mitigate its inherent deleterious effects. Various techniques have been described, including autologous or allogeneic bone grafts for reconstruction and soft tissue realignment to enhance the extensor mechanism.

A 73-year-old male underwent a patellectomy due to a comminuted fracture, subsequently developing osteoarthritis and experiencing a decline in functional status. Concurrent with total knee replacement, we conducted a patellar reconstruction, incorporating routine bone cuts and utilizing bone chips to fashion a new patella. This intervention resulted in the restoration of full extension and improvement of knee function.

Patellar reconstruction demonstrates benefits on knee mechanics and stabilization, contributing to enhanced outcomes and satisfaction following knee replacement. We present an affordable technique for managing patellectomized patients undergoing total knee replacement.

There are several imaging-based measurements for patellofemoral height, which are obtained from sagittal images. However, these methods can be misleading with sagittal oblique slices and when the patella is tilted and/or chronically subluxated. This study aimed to describe a simple method of measuring patellar height using axial patellotrochlear overlap (APTO) on MRI.

A retrospective observational study of 97 knees from 251 patients, excluding those with fractures, massive effusion, or patellofemoral conditions. APTO was measured as follows: (1) patellar length (P) - expressed as the number of axial images showing patellar articular cartilage; (2) trochlear overlap (T) - the number of axial images showing the overlap between patellar articular cartilage and articular cartilage of the lateral trochlea. APTO is the ratio T/P. All measurements were performed independently by six raters on two separate occasions. The raters were two orthopaedic consultants, one knee surgery fellow, two consultant musculoskeletal radiologists, and one radiology fellow. The conventional patellotrochlear index (PTI) was measured as a control for all patients by a senior musculoskeletal radiologist.

The mean APTO value was 36.7% (range 14.2-66.6; standard deviation 11.4). There was a positive correlation with the PTI, Pearson correlation coefficient: 0.76, P < 0.001. Intra-observer reliability was good (intraclass correlation coefficient(ICC): 0.66, 95% confidence interval (CI) 0.54, 0.76, P < 0.001). Inter-observer reliability was fair (ICC: 0.51, 95% CI 0.41, 0.6, P < 0.001).

APTO was shown to be a reliable measurement of patellar height and correlated with existing PTI for patellar height. Measurement of APTO on MRI could be a reliable alternative for the evaluation of patellar height. However, further studies are required to assess its validity in patients with patellofemoral pathology.

There is growing interest in the use of robotic TKA to improve accuracy of component positioning in Total Knee Arthroplasty (TKA). The aim of this study was to investigate the accuracy of implant component position using the ROSA® knee system with specific reference to Joint Line Height, Patella Height and Posterior Condylar Offset (PCO).

This was a retrospective review of a prospectively-maintained database of the initial 100 consecutive TKAs performed by a high volume surgeon using the ROSA® knee system. Both the image-based and imageless workflow were used and two prosthesis types were implanted. To determine the accuracy of component positioning, the immediate post-operative radiograph was reviewed and compared with the immediate pre-operative radiograph with regards to Joint Line Height, Patella Height and Posterior Condylar Offset.

100 consecutive patients undergoing TKA using the ROSA system were included; mean age 70 years (range 49-95 years). Mean change in joint line height was 0.2 mm, patella height (Insall-Salvati ratio) 0.01 and posterior condylar offset 0.02 mm; there was no statistically significant difference between the pre and post-operative values. No difference was demonstrated between image-based or imageless workflows, or between implant design (Persona versus Vanguard) regarding joint line height, patella height and PCO.

This study validates the use of the ROSA® knee system in accurately restoring Joint Line Height, Patella Height and Posterior Condylar Offset in TKA surgery. No significant differences were found between imageless and image-based groups, or between implant designs (Persona versus Vanguard).