Subsidence of Modular Fluted Tapered Stems After Femoral Revision Surgery: Risk Factors and a Novel Classification System

Background Modular fluted tapered (MFT) stems are widely used in femoral revision surgery for their ability to achieve diaphyseal fixation in the setting of bone loss. This study aimed to identify factors influencing MFT stem subsidence. Methods We retrospectively analyzed a cohort of 443 femoral revision procedures performed at a single institution, all using the same model of MFT stem. A total of 180 procedures met the inclusion criteria (≥ four radiographs) and were analyzed for subsidence during follow-up using a radiographic analysis. The mean radiological follow-up was 28.5 months (range, one to 120). Subsidence ≥ five mm was defined as excessive. Implant survivorship was assessed by rerevision rate. The relationship between clinical variables and excessive subsidence was examined using logistic regression and Bayesian modeling, guided by a directed acyclic graph. Results The mean stem subsidence at 12 months was 1.6 ± 2.3 mm. Among the full cohort, 18 stems (5.0%) underwent rerevision at a mean of 71.4 months. Excessive subsidence (≥ five mm) was observed in 8.3% of cases. Associative analysis identified severe bone defects (Paprosky IIIA to IIIB) as the main factor associated with excessive subsidence (odds ratio = 6.35, P = 0.001). Short MFT stems, extended trochanteric osteotomies, and men showed weaker, nonsignificant associations. Causal modeling confirmed the influence of bone defect severity and stem length and revealed that sex, age, weight, and height-modulated subsidence risk. Conclusions Short MFT stems and severe bone defects were associated with higher subsidence risk, while patient factors such as age, weight, and height-modulated this risk. Individualized implant choice and structured radiographic monitoring are essential to optimize outcomes in femoral revision surgery using MFT stems.