Developmental dysplasia of the hip (DDH) is the most common deformity of the lower extremity in children. The biomechanical change during closed reduction (CR) focused on cartilage contact pressure (CCP) has not been studied. Thereby, we try to provide insight into biomechanical factors potentially responsible for the success of CR treatment sand complications by using finite element analysis (FEA) for the first time.

Finite element models of one patient with DDH were established based on the data of MRI scan on which cartilage contact pressure was measured. During CR, CCP between the femoral head and acetabulum in different abduction and flexion angles were tested to estimate the efficacy and potential risk factors of avascular necrosis (AVN) following CR.

A 3D reconstruction by the FEA method was performed on a 16 months of age girl with DDH on the right side. The acetabulum of the involved side showed a long, narrow, and "flat-shaped" deformity, whereas the femoral head was smaller and irregular compared with the contralateral side. With increased abduction angle, the stress of the posterior acetabulum increased significantly, and the stress on the lateral part of the femoral head increased as well. The changes of CCP in the superior acetabulum were not apparent during CR. There were no detectable differences in terms of pressure on the femoral head.

Severe dislocation (IHDI grade III and IV) in children showed a high mismatch between the femoral head and acetabulum. Increased abduction angle corresponded with high contact pressure, which might relate to AVN, whereas increased flexion angle was not. Enhanced pressure on the lateral part of the femoral head might increase the risk of AVN.

This study utilized a computational biomechanical model and applied the least energy path principle to investigate two pathways for closed reduction of high grade infantile hip dislocation. The principle of least energy when applied to moving the femoral head from an initial to a final position considers all possible paths that connect them and identifies the path of least resistance. Clinical reports of severe hip dysplasia have concluded that reduction of the femoral head into the acetabulum may occur by a direct pathway over the posterior rim of the acetabulum when using the Pavlik harness, or by an indirect pathway with reduction through the acetabular notch when using the modified Hoffman-Daimler method. This computational study also compared the energy requirements for both pathways. The anatomical and muscular aspects of the model were derived using a combination of MRI and OpenSim data. Results of this study indicate that the path of least energy closely approximates the indirect pathway of the modified Hoffman-Daimler method. The direct pathway over the posterior rim of the acetabulum required more energy for reduction. This biomechanical analysis confirms the clinical observations of the two pathways for closed reduction of severe hip dysplasia. The path of least energy closely approximated the modified Hoffman-Daimler method. Further study of the modified Hoffman-Daimler method for reduction of severe hip dysplasia may be warranted based on this computational biomechanical analysis. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1799-1805, 2017.

Many children with developmental dislocation of the hip especially in underdeveloped countries reach walking age and still remain undiagnosed, which can be detrimental to their growth and development. Because of the lack medical services often encountered in these regions, it would be attractive to find a cheap and effective treatment. Our work evaluated the results of treatment of these children by closed reduction with or without adductor tenotomy in a prospective study.

We included 20 patients in this study with 29 affected hips (15 right and 14 left). Nine patients (45%) had bilateral DDH and 11 (55%) had unilateral DDH. There were 18 girls (90%) and two boys (10%) who were followed up for a mean of 21 mo (18-24 mo). Ages ranged from 9 to 36 mo (mean age 18.3 mo). Patients were divided according to age into two groups: between 9-18 mo and from 19-36 mo. The first group included nine patients (14 hips) while the second had 11 patients (15 hips).

In the first group, closed reduction failed in two patients (two hips) during the follow-up period (14.3%) and this necessitated shift to open reduction, while in the second group only one patient (bilateral DDH) had a similar failure (13.3%). We identified four hips with avascular necrosis. Three of them required no further treatment, the remaining hip was openly reduced.

Closed reduction in older children offers a valid and reproducible treatment modality in the hands of an experienced pediatric orthopaedic surgeon as long as there is close follow-up and thorough knowledge of possible complications and their management including the ability to shift timely to open reduction.

We describe our experience in the reduction of dislocation of the hip secondary to developmental dysplasia using ultrasound-guided gradual reduction using flexion and abduction continuous traction (FACT-R). During a period of 13 years we treated 208 Suzuki type B or C complete dislocations of the hip in 202 children with a mean age of four months (0 to 11). The mean follow-up was 9.1 years (five to 16). The rate of reduction was 99.0%. There were no recurrent dislocations, and the rate of avascular necrosis of the femoral head was 1.0%. The rate of secondary surgery for residual acetabular dysplasia was 19.2%, and this was significantly higher in those children in whom the initial treatment was delayed or if other previous treatments had failed (p = 0.00045). The duration of FACT-R was significantly longer in severe dislocations (p = 0.001) or if previous treatments had failed (p = 0.018). This new method of treatment is effective and safe in these difficult cases and offers outcomes comparable to or better than those of standard methods.

Biomechanical factors influencing the reduction of dislocated hips with the Pavlik harness in patients of Developmental Dysplasia of the Hip (DDH) were studied using a three-dimensional computer model simulating hip reduction dynamics in (1) subluxated and (2) fully dislocated hip joints. Five hip adductor muscles were identified as key mediators of DDH prognosis, and the non-dimensional force contribution of each in the direction necessary to achieve concentric hip reductions was determined. Results point to the adductor muscles as mediators of subluxated hip reductions, as their mechanical action is a function of the degree of hip dislocation. For subluxated hips in abduction and flexion, the Pectineus, Adductor Brevis, Adductor Longus, and proximal Adductor Magnus contribute positively to reduction, while the rest of the Adductor Magnus contributes negatively. In full dislocations all muscles contribute detrimentally to reduction, elucidating the need for traction to reduce Graf IV type dislocations. Reduction of dysplastic hips was found to occur in two distinct phases: (a) release phase and (b) reduction phase.

The purpose of this study was to evaluate the long-term results of 43 patients who underwent two-stage operative treatment of late developmental displacement of the hip (LDH). The average age at the time of open reduction was 20.7 months. An intertrochanteric osteotomy was performed after an average of 6.7 weeks. The mean clinical and radiological follow-up was 32.75 years. Degenerative changes were documented according to Kellgren. For assessment of outcome we used Severin's classification and score according to Merle d'Aubigné. One patient required a total hip replacement. Complications included one superficial infection and three recurrent dislocations. One patient developed coxa magna and two additional avascular necrosis of the hip. The score according to Merle d'Aubigné was 16.1. At the latest follow-up 35 hips had degenerative changes grade 0 or 1 and 7 grade 2. Using the Severin classification 13 hips had a satisfactory result (class I), 14 were rated as class II, 7 as class III, 5 as class IV and 2 as class V. The two-stage procedure seems to be a successful principle in the operative treatment of LDH.