Dual mobility in primary total hip arthroplasty: A temptation from the devil or a blessing from above

Abstract

Dual mobility (DM) bearings have gained significant attention in the field of total hip arthroplasty (THA) as a valid treatment option in cases of revision for instability after THA whereas its use in primary THA is still a matter of debate. This manuscript explores the pathology, incidence, diagnosis, treatment options, prognosis, ongoing studies in the literature, and future perspectives related to the use of DM bearings employed in primary THA. DM bearings are primarily designed to address one of the major concerns in THA: Instability of the prosthetic hip. Instability is both for the surgeon and the patient a devastating postoperative complication, leading to significant pain and subsequent apprehension by the patient and may require revision surgeries. The use of DM implants poses the worry of wear-related complications, such as accelerated polyethylene wear and osteolysis, which also pose challenges to long-term implant survival. This technique has seen a steady rise in recent years, with multiple studies reporting favorable outcomes. The incidence of their utilization varies among institutions and surgeons, reflecting differing preferences and patient populations. The diagnosis of instability and wear-related complications in THA often involves clinical assessment, imaging modalities such as X-rays, computed tomography scans, and sometimes advanced imaging techniques like magnetic resonance imaging. DM bearings can be considered as an option when patients present neurologic pathologies such as Parkinson's disease or recurrent dislocations after THA. DM bearings provide an additional articulation point within the implant, facilitating a greater range of motion and inherent stability. This design allows for reduced risk of dislocation and improved functional outcomes. Various implant manufacturers offer different designs and sizes of DM bearings to suit individual patient needs. Current literature suggests that the use of DM bearings in primary THA has demonstrated promising outcomes in terms of enhanced stability, reduced dislocation rates, and improved patient satisfaction. However, long-term studies with larger patient cohorts are necessary to establish the durability and longevity of these implants. Several ongoing studies are investigating the role of DM bearings in primary THA. These studies focus on evaluating long-term implant survivorship, assessing wear patterns, analyzing patient-reported outcomes, and comparing the effectiveness of DM bearings with traditional THA designs. The future of DM bearings in primary THA holds potential for further advancements. Research efforts are aimed at refining implant materials, optimizing designs, and studying the influence of surgical techniques on implant performance. Additionally, continued investigation into the long-term outcomes and cost-effectiveness of DM bearings will play a crucial role in shaping their future use. While further research is warranted, the current evidence supports their potential as a beneficial solution in improving surgical outcomes and patient satisfaction.

Key Words: Dual mobility; First implant; Hip arthroplasty; Surgical technique; Differential diagnosis

Core Tip: In total hip arthroplasty (THA), dual mobility (DM) bearings have drawn interest as a means of managing instability, especially in revision instances. Post-THA instability is a serious issue that could result in discomfort and changes. DM bearings lower the danger of dislocation and improve stability. While wear-related problems are concerning, new research shows positive results. Clinical evaluation and imaging tests, such as computed tomography and X-rays, are necessary for diagnosis. Long-term trials are required to determine durability, but current literature indicates favorable results in primary THA, including improved stability and patient satisfaction.

INTRODUCTION

Total hip arthroplasty (THA) has undergone significant advancements over the years, with the introduction of dual mobility (DM) bearings emerging as a key development. These bearings have gained attention as an effective solution for reducing dislocation risk in THA, particularly in revision surgeries. However, their application in primary THA remains a topic of ongoing debate within the orthopedic community. This manuscript delves into the intricacies of DM bearings, exploring their pathology, incidence, diagnosis, treatment options, prognosis, ongoing studies, and future perspectives in the context of primary THA[1-3].

Historical context and rationale for DM implants

The roots of DM implants trace back to the 1970s when they were conceptualized to enhance the range of motion before encountering joint impingement, a critical factor contributing to hip dislocation. While these constructs have demonstrated success in minimizing dislocation risk in THA, concerns linger regarding potential wear-related complications due to the double-bearing surface, posing challenges such as accelerated polyethylene wear and osteolysis[4-6].

Current landscape and utilization trends

In recent years, DM implants have witnessed a steady rise in popularity, with various studies reporting favorable outcomes. The utilization of these implants, however, varies among institutions and surgeons, reflecting diverse preferences and patient demographics. The incidence of their use in primary THA raises questions about the criteria governing their application in this context, calling for standardized guidelines[7,8].

Diagnostic approaches and patient selection

The diagnosis of instability and wear-related complications in THA involves a multifaceted approach, including clinical assessment and imaging modalities such as X-rays, computed tomography (CT) scans, and, in some cases, advanced techniques like magnetic resonance imaging (MRI). Patient populations presenting with neurologic pathologies, such as Parkinson's disease or recurrent dislocations after THA, stand out as potential candidates for DM bearings.

Theoretical advantages and concerns

DM bearings offer an additional articulation point within the implant, providing an extended range of motion and inherent stability. While they show promise in reducing dislocation risk and improving functional outcomes, concerns persist about wear-related complications, necessitating a careful balance in their application[9,10].

Current literature and ongoing studies

Current literature suggests promising outcomes for DM bearings in primary THA, with enhanced stability, reduced dislocation rates, and improved patient satisfaction. However, the need for long-term studies with larger patient cohorts is evident to establish the durability and longevity of these implants. Ongoing studies are actively investigating various aspects, including long-term survivorship, wear patterns, patient-reported outcomes, and comparisons with traditional THA designs.

Future perspectives and research directions

The future of DM bearings in primary THA holds potential for further advancements. Ongoing research efforts focus on refining implant materials, optimizing designs, and studying the influence of surgical techniques on implant performance. Continued investigation into long-term outcomes and cost-effectiveness will play a pivotal role in shaping the future use of DM bearings.

In summary, while the use of DM bearings in primary THA presents both theoretical advantages and concerns, current evidence indicates their potential as a valuable solution for improving surgical outcomes and patient satisfaction. As research in this field progresses, refining the criteria for patient selection and addressing potential complications will be crucial in unlocking the full potential of DM implants in primary THA[11,12].

METHODOLOGY

Search strategy

The review was performed by using PubMed (https://pubmed.ncbi.nlm.nih.gov) and Reference Citation Analysis (RCA) (https://www.referencecitationanalysis.com) to identify studies related to DM bearings in primary THA. The search strategy aimed to retrieve articles published between 2013 and November 2023. The following combination of keywords was employed: "Dual mobility first implant" and "Dual Mobility total hip arthroplasty first implant." The search was limited to articles published in the English language.

Study selection criteria

Titles and abstracts of the retrieved studies were independently screened by two authors (Boerci L and Buonanotte F) to assess their relevance to the review's objectives. Studies were included if they met the following criteria: (1) Pertinence to DM implants in primary THA; (2) Publication between 2013 and November 2023; (3) Full-text availability; and (4) Exclusion of editorial comments, case reports, letters to the editor, book chapters, historic reviews, non-English language publications, and unpublished articles.

Any discrepancies in study selection were resolved through discussion between the two authors, and a third author (Zeppieri M) was consulted if consensus could not be reached.

Data extraction

Data extraction was performed independently by the same two authors (Boerci L and Buonanotte F) using a predefined template. The extracted information included study characteristics (e.g., author names, publication year), patient demographics, study design, surgical techniques, outcomes, and key findings related to DM implants in primary THA.

Quality assessment

The methodological quality of the included studies was assessed using relevant quality assessment tools, considering study design, sample size, data collection methods, and potential sources of bias. This step aimed to ensure the inclusion of high-quality evidence in the review.

Data synthesis

A narrative synthesis approach was employed to summarize and analyze the findings from the selected studies. The synthesis involved organizing and interpreting the data to address the key objectives of the review, including the benefits, drawbacks, and considerations associated with the use of DM bearings in primary THA.

Ethical considerations

As this review involved the analysis of previously published data, ethical approval was not required. All data were handled confidentially, and the study adhered to ethical guidelines outlined in the Declaration of Helsinki.

DIAGNOSIS

Diagnosing complications related to DM implants in primary THA involves a multifaceted approach, combining clinical assessment with various imaging modalities. Clinical evaluation includes a thorough examination of the patient's symptoms, gait analysis, and assessment of range of motion. Imaging techniques, such as X-rays, CT scans, and, in certain cases, advanced imaging like MRI, play a crucial role in identifying instability and wear-related complications[6].

In cases where neurologic pathologies are present, such as Parkinson's disease or recurrent dislocations after THA, DM bearings may be considered as an option. These imaging tools aids in the early detection and management of complications, ensuring timely intervention and improved patient outcomes[5].

ADVANTAGES

DM bearings in primary THA offers several advantages, including enhanced stability, reduced dislocation rates, and improved functional outcomes. Long-term studies of first-generation DM implants have demonstrated their effectiveness in reducing the risk of revision due to dislocation compared to standard prosthetic implants. Additionally, DM constructs (DMC) have shown positive outcomes in patients with spinopelvic stiffness and neurologic disorders, making them a valuable option in specific clinical scenarios[1,2,13,14].

DISADVANTAGES

Despite the advantages, DM implants pose certain drawbacks. Concerns include increased wear in younger and more active patients, potential for intraprosthetic dislocation (IPD), and higher associated costs compared to standard THA. The generation of wear debris in modular DM implants can lead to complications, and issues like IPD may necessitate additional procedures[4,7].

SELECTION CRITERIA

Determining the appropriate candidates for DM implants involves careful consideration of various factors. Traditionally used as a first implant inpatients prone to dislocation, the selection criteria have expanded over time. Recent reviews suggest that with modifications in implant designs and increasing experience, DM implants are becoming the implant of choice in primary THA, regardless of patient characteristics[6,9].

PROGNOSIS

Estimating the survival of DM THA as a primary implant involves considering factors such as cost and outcomes. While newer designs aim to address previous system failures, the literature supports comparable results between DM implants and standard bearing implants. The prognosis suggests acceptable survival at 5 and 10 years, but long-term studies are needed to confirm durability and assess the cost-effectiveness of these implants[11,12].

SURGERY

Techniques and evolution of DM implants in primary total hip arthroplasty

New designs of DMC have been developed to reduce principal mechanisms of failure of the previous systems. The non-inferiority of results of DM implants compared to the standard bearing can be considered a valid solution in primary THA in patients with a higher risk of dislocation. Patients with femoral fracture, older age, neurological problems, and posterolateral approach are at higher risk of dislocation and could take advantage of DMC[15,16].

Historical evolution of DM implants

DM cups consist of three joints: The inner joint, the smaller one, between the femoral head and the polyethylene liner, the outer larger joint between the metal cup and the polyethylene liner, and the “virtual” third joint between the stem neck and the peripheral border of the liner[1].

DM implants have undergone a significant evolution since their introduction in the 1970s. Initially designed to address the challenge of instability in THA, these implants were primarily utilized in revision surgeries for prosthetic hip instability. Over time, advancements in material science, implant design, and surgical techniques have expanded the application of DM implants to primary THA[17].

The first generation cup design was based on a “supra-hemispherical, cylindrical-shaped edge” configuration. Fixation was supplemented by a tripod anchorage, which consisted of two pegs (for the ischium and the pubis) and one superior screw (for the iliac wing). This design was associated with higher rates of aseptic loosening and IPD.

The second DMC generation, available since the early 2000s, differs from the previous by its material characteristics, anchoring surface pattern, and above all, surface coatings. Press-fit fixation was the most used design instead of the tripod fixation. Osseointegration was improved thanks to plasma spraying with hydroxylapatite over the cups.

Third-generation DM cups have been available since 2010. Their innovation consists of a hemispherical anatomical metal cup that avoids conflicts with the psoas muscle. The new cobalt-chromium alloy, with a mirror-polished internal surface without holes, resists better to wear and deformation. Stability and bone integration are guaranteed by a double-layer plasma spray of titanium and hydroxyapatite. The polyethylene liner has a new design in the periphery to avoid impingement with the third joint[18].

Surgical techniques and implant designs

Modern DM implants are predominantly modular and comprise an acetabular shell, an inner modular metal liner, a polyethylene jumbo head, and a small ceramic or metalhead connected to the prosthetic stem. This modular design allows for flexibility in addressing various patient anatomies and optimizing stability. Monoblock (non-modular) DM designs integrate the articulating surface with the acetabular shell, providing an alternative approach[6,8].

Variants of DM implant procedures

Variants of DM implant procedures have emerged to cater to specific clinical scenarios. Cemented DM implants, for instance, are utilized in both primary and revision surgeries. A systematic review by Ciolli et al[8] concluded that cemented DM cups represent an effective treatment option with favorable clinical outcomes[8].

Evolution of surgical approaches

The choice of surgical approach is a critical consideration in the success of DM implants. Traditionally, the posterior approach has been widely used for THA. However, with the rise of minimally invasive techniques, the anterior approach has gained popularity. Studies suggest that the posterior approach is associated with a higher risk of dislocation, prompting the use of DM implants to enhance stability[11,12].

Contraindications of surgery

While DM implants offer advantages, certain contraindications must be considered. Patients with specific comorbidities or anatomical issues may not be suitable candidates. Factors such as acetabular deficiency, abductor deficiency, prior acetabular fracture fixation, or high-demand physical activity may increase the risk of dislocation and loosening, influencing the decision to use DM implants[8].

Patient age and DM implants

As patient demographics evolve, considerations regarding the age of patients undergoing THA become crucial. Recent studies, including one by Zampogna et al[9], suggest that DM implants play a significant role in younger patients (under 55 years), offering lower complication rates, increased survivorship, and positive patient outcomes[9].

Neurological disorders and DM implants

Patients with neurological disorders, such as cerebral palsy, parkinsonism, or traumatic brain injury, pose unique challenges in THA. However, DM implants have shown promise in reducing dislocation rates in such cases. Conditions like Parkinson's disease or recurrent dislocations after THA may prompt the consideration of DM implants[2].

In elderly patients with a history of stroke, Lang and others describe an improved post-operative quality of life after DMC-THA compared to Internal fixation in case of severe neuromuscular dysfunction of the lower extremity[19].

When compared to a hemiarthroplasty, no difference was found in terms of dislocation rate by the Swedish Registers. DMC should be considered in the case of patients suitable for THA implants for femoral neck fractures[3].

Spinal stiffness and DM implants

Patients with spinal stiffness due to spinal fusion or lumbar degenerative disease are at an increased risk of dislocation. DM implants have been identified as a viable option to reduce hip instability in primary THA in such cases. Alterations in spinopelvic mechanics and pelvic anteversion can be mitigated by the inherent stability provided by DMC[2].

DM in neurological patients with femoral fractures

In the context of femoral fractures in elderly patients with neuromuscular disorders, the use of DM implants have demonstrated comparable results to other patient populations. Studies, including one by Ryu et al[4], suggest that DM implants may be beneficial in the management of displaced femoral fractures in patients with neuromuscular disorders.

LIMITATIONS

DM implants in primary total hip arthroplasty

Despite the promising outcomes associated with DM implants in primary THA, several limitations need to be acknowledged. These limitations encompass aspects related to the implant itself, patient factors, and the evolving nature of surgical techniques. Understanding these limitations is crucial for optimizing patient selection and managing potential challenges.

Wear-related complications

Wear modes in DM cups are the same as described for standard cups. However, one of the primary concerns associated with DM implants is the potential for wear-related complications, for the additional surfaces possible source of debris. Osteolysis and loosening could be complications of this increased wearing[20].

McKellop[21] developed a classification for modes of wear[21] (Table 1).

Table 1 McKellop classification.

Mode	Wearing surfaces
Mode 1	Between two bearing surfaces contacting each other
Mode 2	Between a bearing and a nonbearing surface
Mode 3	When an abrasive third body is interposed between two bearing surfaces
Mode 4	Between two nonbearing surfaces

Modular DM implants generate wear debris at these different interfaces; between the prosthetic head and the polyethylene jumbo head, as well as between the polyethylene jumbo head and the acetabular cup. Younger and more active patients, in particular, may experience higher wear rates, raising concerns about elevated metal ion levels and accelerated polyethylene wear[4].

Differences in wearing rate between cemented and cementless cups were taken into consideration, but the findings support that they have similar results with highly crosslinked vitamin-E-infused liners when used for primary THA surgery[22].

IPD

IPD remains a distinct complication associated with DM implants. Factors such as polyethylene wear, aseptic loosening, and blocked articulation between the liner and metal cup can contribute to this complication[6,23].

Three types of intraprostatic dislocations have been described: In the first type there is uniform wear of the external liner (46% of IPD); in the second the head center of rotation is altered due to asymmetric wear of the external liner (39% of IPD); the third is associated with intra-articular particles or metallosis caused by rapid wear of the retentive edge[4,16].

Although advancements in design and materials have reduced the incidence of IPD, it remains a consideration in the long-term performance of these implants[17].

Costs and economic considerations

While DM implants offer clinical advantages, their higher associated costs compared to standard THA implants remain a limitation. The economic implications of utilizing DM implants should be carefully considered, especially in the context of cost-effectiveness analyses and the financial constraints of healthcare systems[7].

Surgical approach considerations

The choice of surgical approach is a critical factor influencing the success of DM implants. While posterior approaches have traditionally been common in THA, the rising popularity of minimally invasive anterior approaches introduces a new set of considerations. Some studies suggest that the posterior approach is associated with a higher risk of dislocation, necessitating the use of DM implants. However, reported dislocation rates with posterior approaches are still higher compared to other approaches[11,12].

FUTURE PERSPECTIVES

Advancements in material science and design

The future of DM implants in primary THA holds promise for continued advancements in material science and implant design. Ongoing research efforts focus on developing more durable materials, such as vitamin E-infused highly cross-linked polyethylene, which aims to reduce oxidative degradation and improve long-term wear resistance[4].

Long-term outcome studies and implant survivorship

Robust, long-term outcome studies with larger patient cohorts are essential to establish the durability and survivorship of DM implants in primary THA. Research endeavors should focus on evaluating implant performance, wear patterns, and patient-reported outcomes, and comparing the effectiveness of DM implants with traditional THA designs[1].

Refinement of surgical techniques

Future research should delve into the influence of surgical techniques on the performance of DM implants. This includes studying the impact of different approaches, such as posterior and anterior approaches, on implant stability and dislocation rates. Optimizing surgical techniques can contribute to enhanced patient outcomes and reduced complication rates[11,12].

DISCUSSION

The exploration of DM in primary THA represents a significant stride forward in the pursuit of optimal outcomes and enhanced stability in hip joint replacement surgery. There are multifaceted aspects of DM implants, which promote their biomechanical advantages, clinical efficacy, and potential impact on patient satisfaction and long-term implant survivorship. The biomechanical rationale behind DM design, encompassing increased range of motion and decreased dislocation rates, emerges as a cornerstone of its appeal. By fostering a greater arc of motion and providing additional constraints to dislocation, these implants address one of the persistent challenges in surgery. The biomechanical synergy between the inner and outer articulations, as discussed in this review, contributes not only to stability but also to the mitigation of wear and potential complications associated with traditional hip implants.

Clinical studies and analyses featured in this manuscript consistently highlight the notable reduction in dislocation rates associated with DM implants, emphasizing their clinical efficacy and the potential to enhance patient outcomes. The accumulated evidence underscores the relevance of DM in mitigating one of the most common and vexing complications in surgery, thereby presenting a viable solution for both surgeons and patients alike. Furthermore, the considerations for patient satisfaction and quality of life are pivotal in evaluating the success of any orthopedic intervention. While the existing body of evidence is compelling, the review also acknowledges the need for ongoing research to further refine our understanding of DM implants. Long-term studies and comparative analyses with traditional implants, as well as investigations into potential complications unique to DM, will be crucial in solidifying its role in the armamentarium of orthopedic surgeons.

CONCLUSION

The integration of DM implants in primary THA holds great promise. This review consolidates the current knowledge surrounding DM, emphasizing its biomechanical advantages, clinical effectiveness, and positive impact on patient satisfaction. As we stride into the future of orthopedic surgery, the exploration and refinement of DM implants stand as a testament to the commitment of the orthopedic community to optimize patient outcomes and redefine the standards of excellence in hip joint replacement surgery.