(P 474) PREDICTORS OF EARLY INTROWTH AND FAILURE FOLLOWING SHORT COMPRESS SPINDLE OSSEOINTEGRATION FIXATION AT THE LOWER EXTREMITIES

Objective: Limb salvage with endoprosthetic replacement (EPR) via compressive osseointegration allows for fixation within a short segment of bone. Two spindle lengths are available, requiring either 45mm (short) or 80mm (standard) of residual bone. The aim of this study is to report on predictors of early ingrowth and failure in an exclusively short spindle cohort.

Methods: From 2013-2022, 43 patients (mean age 28.3±15.9 years; 21M,22F) were treated with lower extremity compressive osseointegration EPR (30 distal femur, 10 proximal femur, 3 proximal tibia). Indications were following primary tumor resection (29) or revision arthroplasty (14). Twenty-two patients underwent chemotherapy postoperatively. No patients in this series underwent extremity radiation therapy. All patients underwent short spindle (45mm) reconstruction. Radiographs were assessed at 3, 6, and 12 months for cortical hypertrophy indicating ingrowth at bone-implant junction.

Results: For patients with available radiographs, hypertrophy at >2 cortices was seen in 22% at 3 months, 65% at 6 months, and 100% at 12 months. Patients undergoing chemotherapy were at increased risk for delayed ingrowth at > 2 cortices at three [OR 13.3, 95% CI 1.8-154.0] and six [OR 7.1; 95% CI 1.5-27.6]. Resection length, weight, PSI, and location did not influence ingrowth. Two patients had early spindle fracture – both failed in varus alignment following distal femoral replacement.

Conclusion: Patients treated with short spindle compressive osseointegration experience delayed cortical hypertrophy on chemotherapy. This did not appear to negatively influence implant ingrowth at 12 months. When utilizing a short spindle, avoidance of varus alignment may reduce early implant failure.