Rotating hinge expandable prostheses may have a higher risk of medial tibial plateau deformity compared to constrained hinged expandable prostheses following reconstruction of distal femur in children with primary bone tumors.

purposeThe distal femur is the most common site for bone sarcoma in children. Expandable prostheses may be used to overcome the resultant limb length discrepancy due to the sacrifice of the growth plate in children who undergo resection of primary bone tumors in the distal femur. Few studies analyzed the complications in children treated with expandable prostheses. Furthermore, to date, no studies evaluated the association between medial tibial plateau deformity and the use of constrained versus rotating hinges expandable prostheses in children who underwent primary bone resection of the distal femur. This study aimed to evaluate the complications and reconstruction survival rates associated with expandable prostheses for the distal femur in children with primary bone tumours, with a particular focus on the risk of tibial plateau deformity related to the use of constrained versus rotating hinge expandable prostheses.

methodsWe performed a retrospective single-centre study of 25 children who underwent distal femur reconstruction with expandable prostheses after resection of primary bone tumours between 2001 and 2024. Eleven children had rotating hinge expandable prosthesis, 14 children had constrained hinge expandable prosthesis, nine children had mechanical expandable prosthesis, and 16 children had magnetic expandable prosthesis. Eight out of 25 children had expandable prosthesis with uncemented femoral stem, and 17 out of 25 children had cemented femoral stem. All 25 children had expandable prosthesis with uncemented tibial smooth stem. The median age of children was nine years (range, 5-14 years). The median follow-up was 9.4 years (range, 1.1-16.5 years).

resultsTwelve out of 25 children (48%) presented complications. The mean number of complications per child was 1.0 (range, 0-2). Aseptic loosening of the femoral stem was observed in four out of 25 children (16%). Periprosthetic fracture occurred in one out of 25 children (4%). Breakage of the hinge component of the prosthesis occurred in one out of 25 children (4%). Infection occurred in two out of 25 children (8%). None of the 14 children with constrained hinged prosthesis presented medial tibial plateau deformity. In contrast, seven out of 11 children (63%) who underwent reconstruction with rotating hinge expandable prostheses presented medial tibial plateau deformity. Overall, nine of the 25 children (36%) had to replace their temporary expandable prosthesis with a definitive standard prosthesis. Reconstruction survival was 79.3% at five years (95% confidence interval 53.7 to 91.7%) and 59.5% at ten years (95% confidence interval 28.3% to 80.1%).

conclusionRotating hinge prosthesis showed a high risk of medial tibial plateau deformity compared to constrained hinged prosthesis. We may recommend the preferential use of constrained hinge expandable prosthesis in children who undergo primary bone tumour resection of the distal femur to reduce the risk of tibial deformity.