CORR Insights®: Is Isolated Mobile Component Exchange an Option in the Management of Intraprosthetic Dislocation of a Dual Mobility Cup?

Where Are We Now?

While certainly not new to the European environment [2, 6], the use of dual mobility bearings for THA has only recently been more widely accepted in North America and Oceania [5, 9]. Recent data from the highly regarded Australian Orthopaedic Association National Joint Replacement Registry suggests that dual mobility construct use has increased more than 10-fold in the last 5 years [1]. While touted by many as the panacea for THA bearing instability—seemingly incorporating the advantages of both the low-friction Charnley hip with the mechanical features of a “large-head” design—the increased use of dual mobility bearings [9] has bought with it a class of novel wear and failure characteristics. Unique to dual mobility (and arguably bipolar) hips are the phenomena of wear between the two articulating heads, and unintended separation of them—the latter being known as intraprosthetic dislocation. Although these are thought to be uncommon, they can be challenging to manage when they occur [3].

Wegrzyn and colleagues [10] present one of the largest and most-complete analyses of the survivorship of dual mobility THA constructs to date—5274 hips—with a mean follow up of 14 years. This well-controlled work retrospectively studied 18 years of longitudinally maintained, single-institution registry data of DM use exploring specifically modes of failure and subsequent revision performance. The authors report a nearly 20% five year revision rate for isolated mobile component exchange (with retention of an otherwise well-fixed acetabular shell) and therefore recommend complete acetabular component revision as the standard-of-care for this condition.

Where Do We Need To Go?

While the use of dual mobility THAs remains controversial in some settings, its accepted indications are broadly increasing [2, 3] and now include patients with femoral neck fractures [4], neuromuscular disorders, and revision surgery—especially for instability [5]. However, questions remain as to the longer-term survivorship and patient satisfaction of dual mobility options, especially in younger and/or higher demand individuals. With an ever-increasing societal expectation of implant longevity and enduring high functional performance [8], the onus remains upon advocates of this design type to provide scientifically robust, defendable, and generalizable data to support ongoing and wider application.

Wegrzyn and colleagues [10] studied dual mobility constructs implanted between 1991-2009; several design and surgical technique iterations have taken place since in an attempt to address recognised shortcomings. That being so, future studies like this one in CORR® will be needed to evaluate the current generation of implants as a new benchmark in terms of durability and relevant complication profiles, and can be compared against the results reported herein. Likewise, further studies will need to establish whether these findings generalize well outside a single very-experienced European specialist center.

How Do We Get There?

Conceivably, the only sites doing high enough dual mobility volumes, allowing for the generation of meaningful randomized trials, are the large specialist facilities and referral centers. However, findings derived from such institutions do not always apply well to lower-volume general orthopaedic settings. Also, because meta-analyses depend on such randomized trials (which don’t currently exist), and because multi-center collaborations are usually expensive, difficult, and time-consuming, there is potential value in focusing on data from large national registries [7] to get the information we need more quickly. Registries also, by definition, generalize well to “regular” practice, since they gather data from all practice settings.

Despite the existance of several established, high-quality, national registries—with mandated participation and detailed longer-term data collection—the indices they follow often are relatively crude: Survivorship is emphasized in many instances over patient-reported outcomes (performance). While registries themselves are not without limitation, they may provide a briding means that allows access to high-quality data to fill some of the knowledge gaps currently present with regard to dual mobility bearings and their role in contemporary patient care. Further work inter-linking the benefits of randomized controlled trials with national registry data is an avenue for future investigation.