Femoral Stem Subsidence and its Associated Factors after Cementless Bipolar Hemiarthroplasty in Geriatric Patients

Introduction: Early femoral stem subsidence has been a concern as a predictor of the beginning of implant loosening, especially on cementless hip arthroplasty implants. This study aimed to determine the factors that affect femoral stem subsidence and outcome following hemiarthroplasty in the geriatric population.

Materials and Methods: This is a retrospective study of 179 patients who underwent cementless bipolar hemiarthroplasty during the 2011-2019 period at an orthopaedic and traumatology hospital. Data on the patient's demography, pre-operative American Society Anaesthesiologist (ASA) score, body mass index (BMI), canal flare index (CFI), Dorr classification, and stem alignment were obtained. The primary outcomes were post-operative femoral stem subsidence, post-operative pain, and functional outcome using Harris Hip Score (HHS). Statistical analysis was conducted to identify risk factors associated with the primary outcome.

Results: The mean femoral stem subsidence was 2.16 ±3.4 mm. The mean post-operative Visual Analog Score (VAS) on follow-up was 1.38 ± 1. Mean HHS on follow-up was 85.28±10.3. American Society Anaesthesiologist score 3 (p = 0.011, OR = 2.77) and varus alignment (p=0.039, OR = 6.963) were related to worse stem subsidence. Otherwise, neutral alignment (p = 0.045 and OR = 0.405) gave protection against femoral stem subsidence. The female gender (p = 0.014, OR 2.53) was associated with postoperative pain onset. Neutral alignment had significant relationship with functional outcomes (p = 0.01; OR 0.33).

Conclusion: A higher ASA score and varus stem alignment were related to a higher risk of femoral stem subsidence. Meanwhile, neutral stem alignment had a protective effect on the femoral stem subsidence and outcome.