Revision hip arthroplasty presents a challenge in the setting of femoral bone loss. Tapered stems are susceptible to subsidence which leads to leg length inequality, hip instability and may necessitate repeat femoral revision surgery.

The purpose of this study was to compare radiographic outcomes in two modular tapered revision systems with different distal stem geometries. We sought to establish the minimum postoperative stem bi-cortical contact length that predicts subsidence for tapered stems.

This study examined revision total hip arthroplasties between 2009 and 2016 in a European university affiliated major trauma center. Modular stem A has a taper of 3 degrees whereas modular stem B has a taper of 2 degrees. Radiologic assessment compared x-rays at two time points: immediately post-surgery and most recent x-ray available at a minimum follow up of two years. Leg length discrepancy, subsidence and postoperative bi cortical contact was assessed. Descriptive summary statistics calculated clinical factors (i.e. age, gender, Paprosky classification).

122 arthroplasties were completed. Complete data was available for 112. Revisions were carried out for Paprovski grade 3a/ 3b femoral deficits. Post-operative bi-cortical contact of the proximal stem < 20mm was associated with higher subsidence rates (P = 0.047). Subsidence rates for implant A and B system were 4.27mm (0.12–25.62mm) and 3.43 mm (0.3–11.1 mm) respectively. Significant subsidence was noted in 9.8% (n=8) in implant A and 5.2%(n=2) in implant B.

We conclude that immediate postoperative bi-cortical stem contact of <20mm was associated with significantly higher subsidence rates in this study.