Femoral Stem Subsidence Rate with Cementless Stems in Patients with Sub-capital Femoral Neck Fractures: Relationship to Proximal Femoral Geometry

Introduction: Hip joint replacement surgeries, including total hip arthroplasty (THA) and hemiarthroplasty (HA), are highly successful for treating subcapital femoral neck fractures. However, femoral stem subsidence can negatively impact post-operative outcomes. This study investigates subsidence rates in relation to the geometry of the proximal femur. Methods: A total of 255 patients who underwent cementless HA or THA were included, with follow-up data available for 74 patients who met the inclusion criteria. Pre- and post-operative variables included surgery type, age, sex, ASA score, and rehabilitation method. The cohort was divided into two groups based on femoral stem migration: a low subsidence group (0–4.99 mm) and a high subsidence group (>5 mm). Further subdivision was done according to the proximal femur morphology, which was classified by the Dorr Classification. Results: 44 patients (or 59.5%) were classified as Dorr type A, 27 patients (or 36.5%) were type B, and only three patients (4.1%) were type C. Among patients with Dorr type A, 79.5% had low subsidence, while 20.5% had high subsidence. In Dorr type B, subsidence was nearly equal (51.9% low, 48.1% high). Two Dorr type C patients had low subsidence (66.6%), and one had high subsidence (33.3%). Results were statistically significant (P = 0.042). Multivariate analysis showed that type A patients were likelier to have low subsidence (OR 3.403, CI 1.221–9.486, P = 0.022). Conclusion: The subsidence rate of cementless femoral stems was lower in patients with type A Dorr classification compared to types B and C. These findings suggest that structural geometric differences between the classifications may significantly affect susceptibility to subsidence.