A Prospective Randomized Controlled Trial of Dual-Mobility Components in Primary THA

The aim of this study is to determine if the use of a modular dual mobility bearing is associated with clinically important increases in serum metal levels.

Prosthetic dislocation following total hip arthroplasty (THA) remains a significant concern with a reported incidence of 0.2%-7.0% after primary and 10%-25% after revision THA. The risk of dislocation following THA is multifactorial and includes both surgeon-related factors (i.e. component positioning, surgical approach) and patient-related factors (i.e. gender, age). Dual mobility articulations have been shown to reduce the incidence of hip instability following THA. Dual mobility implants have been used in Europe for over 30 years, but have recently received an increased interest in the United States. Initial dual mobility designs consisted of a cementless, monoblock acetabular component with a highly-polished metal inner bearing surface. Modular dual mobility prostheses have been introduced in which a modular cobalt-alloy liner is inserted into a hemispherical titanium acetabular component. Advantages of this construct include familiarity of use of a standard titanium acetabular component and the ability to use supplemental screw fixation. However, the potential for fretting corrosion between the cobalt-alloy liner and the titanium acetabular component remains a concern. In a retrospective review of 100 consecutive patients undergoing primary THA using a modular dual mobility prosthesis, the authors found 21% of patients to have a serum cobalt level above the normal range, with 9% significantly above normal (\> 1.6 ug/L), at a mean of 27.6 months postoperatively. In addition, a recent prospective cohort study of 26 patients receiving the same prosthesis showed elevated whole blood mean cobalt levels in patients receiving a modular dual mobility prosthesis versus patients receiving a conventional bearing (0.23 + 0.39 vs. 0.15 + 0.07ug/L, p\<0.001) at 1 year postoperatively. Four patients in the dual mobility cohort had a whole blood cobalt level outside the reference range (maximum 1.81 ug/L). To the investigators knowledge no prospective, randomized controlled trial has been performed comparing dual mobility bearings to a conventional single-bearing design. Therefore, the purpose of this study is to compare the use of a conventional single-bearing ceramic-on-polyethylene surface to use of a modular dual mobility bearing in a prospective, randomized controlled setting.