Femoral stem subsidence in cementless total hip arthroplasty: a retrospective single-centre study

PURPOSE AND HYPOTHESIS: Subsidence is a known reason for early failure of total hip arthroplasty (THA). In particular, cementless THA might be vulnerable to migration. The present study analysed femoral stem subsidence after primary cementless THA. Prosthetic and anatomical risk factors for early femoral stem subsidence were evaluated.

METHODS: Two hundred thirty-one consecutive patients who underwent primary cementless THA in a single centre were retrospectively analysed. Post-operative results were evaluated in consideration of prosthetic and anatomical properties in correlation with subsidence on standing pelvic anteroposterior radiographs. Stem type and design, demographic data, BMI, canal flare index (CFI) and canal fill ratio (CFR) were evaluated.

RESULTS: The subsidence rate was significantly higher in collarless femoral stems [3.1 mm (SD 2.8 mm) vs. 1.9 mm (SD 1.5 mm); p = 0.013] while the anatomical type of the proximal femur as described by the canal flare index did not influenced subsidence (p = 0.050). Also, the canal fill ratio showed no significant correlation with subsidence at any level.

CONCLUSIONS: In the present study, stem subsidence was significantly higher in the collarless group compared to collared stems. No anatomical parameter (CFI and CFR) could be identified as risk factor for subsidence. Neither age nor BMI influenced subsidence in this cohort. Still, subgroup analysis indicated a sex-dependent role of BMI. Prospective studies of large cohorts should address the problem of subsidence in the future.

LEVEL OF EVIDENCE: Retrospective therapeutic study, Level IV.