Weight limits associated with commonly used femoral stems for total hip arthroplasty

Background: The global prevalence of obesity is increasing, with a corresponding rise in the proportion of overweight and obese patients undergoing total hip arthroplasty (THA). Although modern high-strength super alloys have reduced the incidence of femoral stem fatigue fractures to between 0.23% and 10.7%, this complication persists. Excessive body mass increases the bending moment acting on the prosthesis, particularly in cases with inadequate proximal medial calcar support, leading to cantilever bending and potential structural failure.

Objective: This study aimed to identify manufacturer-imposed weight restrictions for the most frequently utilized cemented and uncemented femoral stem implants in the United Kingdom, as identified by National Joint Registry (NJR) data.

Key Points: Data from the NJR 10th Annual Report identified the five most common cemented and uncemented stems. Manufacturer inquiries revealed that only the Corail size 6 uncemented stem has a formal weight limit (60 kg). Literature review indicates that fatigue fractures are frequently associated with high body mass index (BMI >25 kg/m²), the use of undersized stems in obese patients, and modular neck-stem junctions. High nitrogen stainless steel (HNSS) stems appear more susceptible to fatigue than cobalt-chrome alloys. Mechanical failure is often propagated by a combination of patient weight, increased offset, and loss of proximal osseous support.

Conclusion: Most common femoral stems lack formal manufacturer weight restrictions despite a clear clinical association between obesity and fatigue failure. Surgeons should prioritize achieving optimal proximal femoral support and consider avoiding small-diameter or high-offset modular stems in overweight populations to mitigate fracture risk.