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

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.

Inclusion Criteria:

- Age between 18 and 80 years

- Willingness to undergo serial postoperative venipuncture for serum meal analysis

- BMI < 40

- Patients that are eligible for the requisite implants as deemed by their surgeon

Exclusion Criteria:

- Clinically significant systemic chronic disease

- Diminished renal function

- Presence of any metal-containing implant outside of the oral cavity

- History of prior hip surgery involving an internal fixation device

- History of hip infection

- Preoperative diagnosis other than osteoarthritis

- Anticipated need for another joint replacement surgery within one year

- Patients taking chromium supplements