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Modular stem hip system yields low survivorship after THA
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Using a modular stem hip system for primary total hip arthroplasty procedures resulted in a low survivorship rate at a minimum of 5 years, according to a recent study.
Investigators evaluated survivorship of the ALFA II modular hip system (Encore Medical/DJO Surgical) among 221 patients who underwent a primary THA with a minimum 5-year follow-up. Twenty-eight patients died of causes unrelated to the surgery before adequate follow-up and 64 patients were lost to follow-up, leaving 129 patients with a mean 6.5-year follow-up.
After the mean 6.5-year follow-up, the modular stem system had an all-cause survivorship rate of 81%. Revision surgery was required by 19.4% of patients; 52% for dissociation of the modular components, 32% for fracture of the prosthesis, 12% for instability/multiple dislocations and 4% for chronic septic THA. BMI and offset were independent risk factors for mechanical failures of the modular stem system.
“The relatively higher number of failures may be because of the increased risk of fretting and corrosion that comes along with modularity at a high stress location and may also be associated with the shape of the femoral taper,” the researchers wrote. “We caution the routine use of primary THA systems featuring modularity at the neck/body junction similar to this design.” – by Casey Tingle
Disclosures: Nahhas reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.
Perspective
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Stuart B. Goodman, MD, PhD, FRCSC, FACS, FBSE, FICORS
The introduction of new technologies is critical to continued progress in treating orthopedic conditions. However, new technologies should fulfill an unmet need and be safe, efficacious and cost-effective. Current methods for performing a total hip replacement have excellent longevity, with 15-year survivorship of over 90% with careful patient selection, modern materials and optimal surgical technique. The addition of a modular femoral trunnion to femoral implants was supposed to give the surgeon added versatility in determining femoral neck length, offset and anteversion at surgery. The study by Nahhas and colleagues reported some disturbing findings concerning one company’s modular femoral trunnion, namely prosthesis survivorship of only 80% after 5 to 8 years follow-up. The main causes of failure included dissociation of the modular neck from the body of the stem, fracture of the prosthesis and residual instability. These outcomes are clearly unacceptable. Based on this study, the utility and safety of this prosthesis incorporating a modular femoral trunnion is questionable at best. Better options include careful preoperative planning and performance of the surgical procedure to optimize biomechanical function under physiologic loads.
Professor, department of orthopedic surgery and bioengineering
Redwood City, California
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