Does surgical approach influence canal fill of the femoral component for THA?

Background: Cementless femoral components in hip arthroplasty require optimal primary stability and long-term osseointegration. Inadequate implant sizing may lead to early loosening, subsidence, or periprosthetic fractures. While morphological variability of the proximal femur is a known cause of undersizing, there is ongoing debate regarding whether specific surgical approaches, particularly the direct anterior approach, increase the risk of suboptimal femoral canal fill.

Objective: This study aimed to evaluate the correlation between four different surgical approaches and the canal fill ratio (CFR) of cementless femoral components, while accounting for host femoral morphology.

Key Points: A retrospective radiographic analysis was performed on 183 patients who underwent primary hip arthroplasty using a single anatomical stem design. Patients were categorized by surgical approach: Heuter (n=40), Rottinger (n=53), modified Hardinge (n=50), and Moore (n=40). Femoral morphology was classified using the Canal Flare Index (CFI) and the Dorr classification (Canal Calcar Ratio). Statistical analysis demonstrated no significant difference in CFR across the four surgical approaches at any of the four measured levels (p > 0.05). Although the Rottinger approach showed slightly higher proximal fill in "normal" shaped canals (p < 0.0091), surgical approach was not a primary determinant of undersizing. Distal and proximal fill ratios were significantly influenced by preoperative femoral morphology (CFI and CCR) rather than the surgical portal used.

Conclusion: Surgical approach does not significantly influence the canal fill of anatomical cementless femoral components. The risk of implant undersizing appears related to femoral morphology and implant design rather than the choice of surgical exposure.