Metal-on-metal (MoM) articulations have been widely explored as an alternative to polyethylene bearings in total hip arthroplasty (THA), with proposed benefits including improved range of motion, lower dislocation rates, and enhanced durability.1 Comprising cobalt and chromium, these MoM bearings gained widespread popularity in the United States, particularly in younger and more active patients looking for longer lasting devices.
The articular surface replacement (ASR) acetabular system (DePuy Synthes) was approved for sale by the US Food and Drug Administration in 2003 and implanted in an estimated 93,000 cases.2 Since then, however, the early failure rate of the prosthesis has been well documented,3-5 leading to a formal global product recall in August 2010. The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) was amongst the first to report a 6.4% rate of failure of the device at 3 years when inserted with a Corail stem.6 An acceptable upper rate of hip prosthesis failure is considered to reach 1% per year, with the majority of implants reporting well below this value. A 10.9% failure rate at 5 years was documented when the prosthesis was inserted for resurfacing. The National Joint Registry of England and Wales confirmed these findings and observed a 13% and 12% rate of failure at 5 years for the acetabular and resurfacing systems, respectively.2 With the notable failure of the ASR system, this study reports our single-center 5-year survivorship experience and evaluates any variable that might be predictive of an early failure to aid in patient counseling.
METHODS
A single-center, single-surgeon, retrospective review of a consecutive series of patients was performed from December 2005 to November 2009. This study included all patients who underwent a primary THA with a DePuy Synthes ASR™ XL Acetabular hip system. No patients were excluded. Institutional Review Board approval was obtained. Patient demographics comprising of age, gender, and body mass index (BMI) were recorded. The primary endpoint of this study was 5-year survivorship rates. Secondary endpoints included duration to revision surgery, blood cobalt and chromium levels, time interval of blood ion tests, acetabulum size, acetabular component abduction angle, and duration to follow-up.
Candidates for the ASR™ XL Acetabular hip system included young patients and/or those considered to be physically active. In a select few, ASR devices were implanted upon patient request.
All patients underwent primary total hip replacement with a DePuy Synthes ASR™ XL uncemented acetabular component and an uncemented femoral stem (DePuy Synthes, Summit, or Tri-Lock) inserted via a standard posterior approach (Figure 1). Acetabulum sizes ranged from 52 mm to 68 mm in diameter.
All patients were followed-up yearly in the outpatient setting. Routine (yearly) metal-ion level sampling (whole blood) was started in 2010 for all patients. Laboratory tests were conducted at a single laboratory (Lab Corp.). Abduction cup inclination angles were measured by the providing surgeon using digital radiology software (GE Centricity systems).
The Student’s t-test was used to compare mean values (such as age, BMI, and metal ion levels) between the failure and no-failure groups. The 2-sided Fisher’s exact test analyzed differences in gender. Simple logistic regression analyzed variables associated with the failure group. Significance was P ≤ .05.
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