(P 102) FACTORS RELATED TO ASEPTIC LOOSENING IN ENDOPROSTHESIS RECONSTRUCTION OF THE PROXIMAL TIBIA

Objective: Endoprosthetic reconstruction is frequently used after tumor resection in the proximal tibia. Among limb salvage procedures, proximal tibia replacement (PTR) is associated with the least favorable outcomes. However, data on factors related to aseptic loosening in modern PTR implants are lacking.

Methods: This was a retrospective review of patients who underwent PTR from 1998 to 2024. The primary endpoint was aseptic loosening. Ratios of the width of the medullary canal to the width of the implant stem at the tibial and femoral diaphysis and femoral metaphysis were measured on anteroposterior (AP) and lateral radiographs to assess fill of the canal by the implant stem. Linear regression was used to identify factors associated with aseptic loosening.

Results: Sixty patients treated with PTR were included. Revision-free survival was 60% at 5 years and 34% at 10 years. Nine patients had revision surgery for aseptic loosening (15%); of these, 7 (11.7%) had femoral loosening while 4 had tibial loosening (6.7%). Compared to patients with stable implants, patients with aseptic loosening had smaller femoral stem size (median 13.0 mm, range 11.0-17.0 vs median 16.0 mm, range 13.0-21.0, p< 0.001). On univariate analysis, tibial stem size 11 mm or larger (odds ratio (OR) 0.23, 95% confidence interval (CI) (0.05-0.99); p=0.048) and femoral stem size 15 mm or larger (OR 0.03, 95% CI (0.00-0.19); p< 0.001) were associated with a lower risk of aseptic loosening. Higher femoral AP ratio (OR 34.5, 95% CI (3.59-630); p=0.001), femoral metaphysis AP ratio (OR 17.3, 95% CI (3.57-165); p< 0.001), and femoral metaphysis lateral ratio (OR 5.73, 95% CI (1.04-40.3); p=0.045) were associated with a higher risk of aseptic loosening. When controlling for confounding variables, femoral stem size less than 15 mm was associated with aseptic loosening (OR 14.7, 95% CI 2.19-145.28; p=0.005).

Conclusion: These findings highlight the importance of careful implant selection in PTR, particularly regarding femoral stem size. Femoral implant canal fill measured on AP and lateral radiographs may help clinicians select the optimal stem size to reduce loosening risk. Further studies are needed to explore strategies to improve implant longevity in this high-risk population.

Univariate Analysis of Factors Associated with Aseptic Loosening