# A Custom Hinged Endoprosthesis for the Treatment of Proximal Tibial Osteosarcoma in Skeletally Immature Patients

## TL;DR

A custom hinged endoprosthesis helps preserve limb growth in children with proximal tibial osteosarcoma, offering good function and fewer complications.

## Contribution

A novel temporary endoprosthesis design preserves growth in skeletally immature pediatric osteosarcoma patients.

## Key findings

- The endoprosthesis preserved 81.4% of distal femoral growth on average.
- Patients achieved an average MSTS score of 27.4, indicating good functional outcomes.
- Limb length discrepancy averaged 2.1 cm with a low complication rate.

## Abstract

Proximal tibial reconstruction is one of the most difficult procedures in limb-preserving surgery for pediatric patients. The resection of the physes in skeletally immature children often results in limb length discrepancy. A custom hinged endoprosthesis was designed for pediatric limb salvage with the preservation of growth originating from the ipsilateral distal femur. The endoprosthesis is intended to be temporary and is eventually converted to an adult modular oncological prosthesis once the child has reached skeletal maturity. This study reported the outcomes of patients treated with this endoprosthesis. The results demonstrate that this custom hinged endoprosthesis can preserve the growth plates in the adjacent femur and provide satisfying functional outcomes with lower postoperative complication rate. It could serve as an alternative for proximal tibial osteosarcoma in skeletally immature children.

Background: The optimal treatment for proximal tibial osteosarcoma (OS) in skeletally immature patients remains controversial. A custom hinged endoprosthesis has been used to preserve the growth potential of the distal femur. This study aims to report (1) the 2-year follow-up outcomes after surgery for pediatric proximal tibial OS; (2) the complications associated with this endoprosthesis; and (3) the extent to which the growth potential of the adjacent open physis can be preserved. Methods: Seven skeletally immature patients (mean age, 11.1 years; range, 9–13 years) with proximal tibial OS were included between November 2020 and December 2022. All underwent tumor resection and reconstruction by this custom endoprosthesis. Postoperative limb function was evaluated by the Musculoskeletal Tumor Society (MSTS) score system and complications were recorded. Overall leg length and femoral length were measured radiographically to determine the growth rate. Results: The mean follow-up time was 34.7 months (standard deviation (SD), 8.9 months). One patient presented with local recurrence 12 months after surgery, and another patient had pulmonary metastasis 3 months postoperatively. The range of flexion of the knee after rehabilitation was between 90° and 125°, with an average of 103.6° (SD, 12.5°). The average MSTS score of the patients after surgery was 27.4 (SD, 1.5). Wound dehiscence took place in three patients after chemotherapy. At the last follow-up, the overall limb length discrepancy was 2.1 cm (SD, 2.4 cm). Growth at the distal femoral physis after surgery was observed in all patients during follow-up, with an average of 81.4% (range, 57.78–100%) of growth of the contralateral distal femoral physis. Conclusions: This custom hinged endoprosthesis can preserve the growth potential of the adjacent distal femur and provide satisfying functional outcomes with lower postoperative complication rate. It could serve as an alternative for proximal tibial OS in skeletally immature children.