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    Dual Mobility Implants for an Unstable THA

    In the abstract from his presentation at ICJR’s Pan Pacific Orthoapedic Congress, Dr. Craig Della Valle shares data showing that dual mobility implants are better than constrained liners for patients who present with dislocation after a total hip arthroplasty.

    By Craig J. Della Valle, MD

    Constrained liners are a tantalizing solution to both prevent and treat instability following total hip arthroplasty (THA), as they markedly increase the force needed for a dislocation to occur.

    They have, however, several important negatives that the surgeon must consider before entertaining their use, including:

    Increased stresses at the implant-bone interface, which can increase the risk of loosening or cause catastrophic failure in the early postoperative period

    Decreased range of motion with a greater risk of impingement, which usually requires an open reduction if the implant dislocates or otherwise fails

    Given the limitations of constrained liners, in the past 5 years our practice has looked to dual mobility articulations as an alternative to constrained liners, including for patients with abductor deficiency.

    We retrospectively compared a consecutive series of revision THA patients who were at high risk for instability and had been treated with either a constrained liner or a dual mobility articulation. Indications for both groups included abductor insufficiency, revision for instability, or inadequate intra-operative stability when trialing.

    Forty-three hips were reviewed in the constrained group (mean follow-up of 3.4 years) and 36 in the dual-mobility group (mean follow-up of 2.4 years). The rate of failure was compared using a Fisher’s exact test with a p-value of < 0.05 considered significant.

    At a minimum of 2 years, there were 10 dislocations in the constrained group (10/43 or 23.3%) compared with 3 in the dual mobility group (3/36 or 8.3%; p = 0.06).

    There were 15 repeat revisions in the constrained group – 10 for instability, 4 for infection, and 1 for a broken locking mechanism – compared with 4 in the dual mobility group – 2 for mechanical failure of the cemented dual mobility liners with dislocation and 2 for infection (34.9% vs. 11.1%; P = 0.01).

    With repeat revision for instability as an endpoint, the failure rate was 23% for the constrained group and 5.5% for the dual mobility group (p = 0.03). Mean Harris Hip Score (HHS) improved from 45 to 76 points in the constrained liner group, and from 46 to 89 points in the dual mobility group.

    Dual mobility articulations offer anatomic-sized femoral heads that greatly increase jump distance, without many of the negatives of a constrained liner. While dual mobility is associated with its own concerns and problems (including intra-prosthetic dislocation and wear), our initial results suggest that they are a viable alternative to a constrained liner, even in the most challenging situations.

    Author Information

    Craig J. Della Valle, MD, is from Rush University Medical Center, Chicago, Illinois.

    References

    1. Wera GD, Ting NT, Moric M, Paprosky WG, Sporer SM, Della Valle CJ. Classification and management of the unstable total hip arthroplasty.J Arthroplasty,27: 710-5, 2012.
    2. Kung PL, Ries MD. Effect of femoral head size and abductors on dislocation after revision THA. Clin Orthop. 465:170-4, 2007.