Radiological modes of fixation of a tapered, wedged proximally coated femoral stem

Background: Tapered wedge femoral stems are designed to achieve proximal metaphyseal fixation, theoretically reducing stress shielding and thigh pain. However, variations in femoral morphology and surgical technique may result in alternative patterns of implant-bone contact, the clinical significance of which remains poorly defined for hydroxyapatite-coated beta-titanium alloy stems.

Objective: This study aimed to classify the radiological fixation modes of a proximally hydroxyapatite-coated tapered stem and evaluate their correlation with clinical outcomes and femoral morphology.

Key Points: A retrospective analysis was conducted on 106 primary total hip arthroplasties with a minimum two-year follow-up. Radiological fit was categorized into five patterns: proximal, distal, combined, three-point, and no-fit. Proximal wedging occurred in only 35% of cases and was significantly associated with Dorr type B femurs (p=0.01). Conversely, distal and combined fits were more prevalent in Dorr type A femurs (p=0.001 and p=0.04, respectively). While three-point fixation showed a trend toward association with thigh pain (p=0.05), overall clinical results, including Hospital for Special Surgery scores, were independent of the fixation mode or bone type. All stems achieved secondary osseointegration without evidence of subsidence or loosening. Severe thigh pain was specifically associated with stems in varus alignment or those where the distal tip contacted the cortex.

Conclusion: Although tapered stems are designed for proximal wedging, diverse fixation patterns occur due to metaphyseal-diaphyseal mismatch. These variations do not compromise short-term clinical outcomes or implant stability, suggesting the versatile fixation capabilities of this stem design.