Correlation of Subsidence with Proximal Femoral Anatomy in Hydroxyapatite-Coated vs Non-hydroxyapatite-coated Collarless Femoral Stems: Radiological Results at a Mean Follow-Up of 4.5 Years.

Background: Subsidence has been identified as a cause of early failure in total hip arthroplasty. Our study's main goal was to examine the subsidence rates of two femoral stem designs-HA-coated and non-HA-coated (grit-blasted) stems-that are used in total hip arthroplasty. The secondary aim of our study was to evaluate the influence of anatomical parameters on subsidence of the femoral stem and to compare the rates of revision for aseptic loosening between these two femoral stem designs. Methods: A retrospective review was conducted of the digital radiographs of 121 consecutive cementless primary total hip arthroplasties with two different types of stems. For the assessment of femoral morphology, we calculated the Canal Flare Index (CFI) and Canal-to-Calcar Ratio (CCR) on pre-operative radiographs. Subsidence was calculated between two radiographs, the immediate post-operative radiograph and the radiograph obtained at the latest follow-up. A threshold of > 3 mm was considered as a clinically significant migration. Results: The mean follow-up duration was 54.04 months. The mean subsidence of the HA-coated stems cohort was 1.02 mm (SD 1.43), and for the non-HA-coated cohort, it was 1.48 mm (SD 0.73). The mean overall subsidence of all 121 THAs together was 0.86 mm. No anatomical parameter (CFI and CCR) or demographic parameter (age, gender) could be identified as a risk factor for subsidence. Conclusion: The presence or absence of HA coating and the proximal femoral morphology had no statistically significant effect on the subsidence of collarless cementless femoral stems.