Abstract

Background: Total hip arthroplasty failures due to adverse local tissue reaction or gross mechanical failure at the femoral head–trunnion junction are being increasingly reported. If the head–trunnion junction is not coupled with enough force (≥ 4 kN), unintended motion can occur between the head and trunnion, increasing the potential for a subsequent adverse local tissue reaction and/or gross mechanical failure. We developed three hypotheses: (1) and (2) surgeons strike metallic and ceramic heads, respectively, with at least one mallet blow producing an effective coupling force ≥ 4 kN, and (3) surgeons strike metallic and ceramic heads with similar force. 

Methods: A surgical simulator capable of measuring forces acting along the central femoral head bore–trunnion axis was constructed. Fifty-five surgeons followed a standardized simulation protocol and were instructed to select a mallet that most closely resembled their surgical mallet and to strike the simulator in a manner identical to their intraoperative head–trunnion coupling routine for 36 mm metallic and ceramic femoral heads.

Results: 25.9% and 16.4% of surgeons applied an effective coupling force ≥ 4 kN for metallic and ceramic heads, respectively. Surgeons applied significantly more force to metallic (3.06 kN) heads than to ceramic (2.62 kN) heads (P<0.001). Demographic data collected from participants was used for additional post-hoc analyses. Surgeons who selected a mallet mass >800 g had 4.23 greater odds of reaching the ≥ 4kN threshold (P=0.047).

Conclusion: This investigation indicates that most total hip arthroplasty surgeons do not apply enough force to optimally couple metallic or ceramic heads to the trunnion. Improved surgical coupling of this junction could decrease the incidence of trunnion-related total hip arthroplasty failure.