CORR Insights®: What Is the Dislocation and Revision Rate of Dual-mobility Cups Used in Complex Revision THAs?

Where Are We Now?

Contemporary data indicate that dislocation has become the most common reason for re-revision after revision THA [7]. Careful soft tissue handling (inclusive of closure); correct positioning of the acetabular and femoral components; minimization of soft tissue, bony, and implant impingement through attentive intraoperative trialing and ROM assessment; large femoral heads; dual-mobility constructs; and constrained liners can be used to improve stability. However, in revision THA, the improved head-neck ratio of large femoral heads often does not suffice. Moreover, although constrained liners have been shown to minimize the risk of dislocation after revision THA [2, 3], reduced ROM and subsequent impingement, excessive wear, risk of disassembly, and increased bone-prosthesis stresses and subsequent loosening make them a less attractive option [1-3].

On the other hand, studies have shown that dual-mobility constructs decrease the risk of dislocation after revision THA without the limitations of constrained liners [7, 10]. For instance, Hartzler et al. [7] showed that dislocation in those receiving a dual-mobility construct was three-fold lower than in those receiving a 40-mm femoral head during revision THA. Moreover, re-revision for dislocation was substantially lower in the dual-mobility group than in the 40-mm femoral head group. This has been reinforced in a large systematic review by Reina et al. [10] that showed dislocation and re-revision for dislocation were also substantially lower after revision THA in the dual-mobility group than in controls.

In this excellent paper by Unter Ecker et al. [11], the authors studied 216 complex revision THAs treated with a cemented dual-mobility construct. They found that dislocation-free survival rates were 96% at 5 years and 82% at 9 years. Moreover, survival free of revision for dislocation was 99% at 5 years and 85% at 9 years. These findings are important because the authors focused on complex revision THAs in which there was substantial bony and soft tissue compromise. These are precisely the type of procedures in which a surgeon may contemplate a dual-mobility construct versus a constrained liner.

Where Do We Need To Go?

Although dual-mobility constructs substantially reduce the risk of dislocation and re-revision for dislocation after revision THA in most series at the mid-term [7, 10], advancements are still needed for patients receiving megaprostheses (such as proximal femoral replacements and total femoral replacements) who have no functioning abductor musculature, as well as for those who have experienced dislocation after reconstruction with dual-mobility constructs or constrained liners. Evidence suggests that both of these are unsolved problems; for example, one study [12] showed that the overall dislocation rate after revision with a proximal femoral implant was nearly 14% at a mean of 2 years postoperatively, although 52% of patients in that series received a constrained liner. On the other hand, another study [5] showed that conversion to a dual-mobility construct can be a salvage option in high-risk patients who have undergone multiple operations with dislocated constrained liners.

In addition, longer-term follow-up is required for the types of dual-mobility constructs used in revision procedures in North America. As opposed to Europe, where dual-mobility constructs were introduced in 1974 and results were first published in 1986, dual-mobility constructs were not available in the United States until 2009 [1].

Finally, because dual-mobility THA bearings with 28-mm femoral heads can experience intraprosthetic dislocations [13], future investigations should focus on solving this problem. In addition, although no series has shown an adverse local tissue response from a dual-mobility construct, some surgeons are concerned with taper corrosion and risk of corrosion with a modular liner [1, 4, 8]. As such, innovations to minimize cobalt and chromium in the construct with ceramic femoral heads and alternative liners are appealing.

How Do We Get There?

In the revision setting, I believe that dual-mobility constructs have been a game changer when it comes to mitigating the risk of dislocation. However, future studies are needed in three main areas: patients receiving megaprostheses who have no abductors, patients in whom the dual-mobility construct is dislocated, and those undergoing two-stage exchange arthroplasty for periprosthetic joint infections. For instance, a recent study has indicated that the risk of dislocation after two-stage exchange arthroplasty for periprosthetic joint infection is prohibitively high, with a cumulative incidence of dislocation of 9% at 1 year [9], an estimate that is substantially worse in those with a megaprosthesis and those with an absent or non-united greater trochanter or abductor deficiency. Studies on dual-mobility constructs based on national registries, such as the American Joint Replacement Registry, provide a ripe area for investigation in these unique cohorts. Ultimately, multicenter randomized clinical trials on constrained liners versus dual-mobility constructs in patients with megaprostheses and large femoral heads versus dual-mobility constructs in reimplantations will provide data to the practicing clinician.