Staged soft tissue lengthening and mega-prosthetic reconstruction for leg length discrepancy after resection of osteosarcoma around the knee

Leg length discrepancy (LLD) is a common long-term complication after resection of osteosarcoma around the knee in skeletally immature patients. We designed a staged strategy that lengthens the limb through distraction with an external fixator, maintains the length with a temporary rod-cement spacer, and completes reconstruction with a static megaprosthesis. In this study, we evaluated its lengthening outcome, functional outcome, and complications. This retrospective study included 22 patients who developed severe LLD of at least 4 cm after tumor resection during skeletal immaturity. All patients completed staged lengthening at our institution between 2019 and 2024. Lengthening outcomes were assessed radiographically. Function was evaluated with the Musculoskeletal Tumor Society score (MSTS-93) and knee range of motion (ROM). Complications were recorded according to the modified Henderson classification. The mean follow-up after completion of lengthening was 37.2 ± 20.6 months. The mean LLD decreased from 97.5 ± 36.4 mm before lengthening to 5.9 ± 15.0 mm at the final follow-up, with a mean gain of 91.6 ± 21.4 mm. The mean MSTS-93 score improved from 35.0 to 91.5%, and the mean knee ROM decreased from 107.0 to 87.5°. The overall complication rate was 22.7% (5 of 22), including four superficial infections, one common peroneal nerve injury, and one prosthetic stem fracture. No deep infection, local recurrence, or distant metastasis was observed. The staged lengthening strategy is a reliable salvage technique for severe LLD following resection of osteosarcoma around the knee in skeletally immature patients, providing satisfactory lengthening and functional outcomes with an acceptable complication profile.