Implant Survival and Clinical Results of a Cementless Femoral Stem: Minimum 30-Year Follow-Up of 348 Primary Total Hip Arthroplasties

BACKGROUND: Cementless femoral stems in total hip arthroplasty (THA) demonstrate excellent survival rates at 20 to 25 years, although evidence beyond this period remains very limited. Therefore, this study aimed to determine the 33-year results of a cementless femoral stem. METHODS: A retrospective evaluation of 348 primary cementless THAs was performed at a single university center using a single straight femoral stem. All patients were prospectively followed for a minimum of 30 years after THA. Kaplan-Meier survival analyses were performed, and function was assessed using patient-reported outcome measures. RESULTS: At a mean follow-up of 33 years (range, 30 to 37), 67% of patients had died of causes unrelated to THA, and 2% were lost to follow-up. A total of 51 femoral stems (14.7%) were revised, 22 (6.3%) because of aseptic loosening, 18 (5.2%) because of periprosthetic femoral fracture, and 11 (3.2%) because of periprosthetic joint infection. At 33 years, Kaplan-Meier stem survival was 79.2% (95% confidence interval (CI): 72.1 to 84.6, THAs at risk: 53) for revision of any cause and 91.6% (95% CI: 87 to 94.6, THAs at risk: 53) for aseptic loosening. An isolated acetabular revision was not associated with a higher risk of stem revision (log-rank, P = 0.703), while undersizing of the stem (canal fill index less than 90%) was identified as a significant risk factor for aseptic stem loosening (log-rank, P = 0.036). The mean Harris Hip Score values showed a gradual, non-significant decline over time. CONCLUSIONS: The straight, cementless femoral stem showed excellent survival and clinical function after 33 years. Undersizing of the stem was associated with a higher risk of aseptic loosening within the first two decades, whereas periprosthetic femoral fractures emerged as the predominant reason for stem revision during the third and fourth decades. Furthermore, these results confirm that well-fixed cementless stems should be retained during isolated cup revision for aseptic cup loosening.