Objective:To evaluate the preliminary clinical efficacy of minimally invasive extendable prostheses in limb-salvage treatment for distal femoral osteosarcoma in children.Methods:A retrospective analysis was conducted on 36 children who underwent reconstruction of bone defects after distal femoral osteosarcoma resection with minimally invasive extendable prostheses at Peking University People's Hospital between December 2021 and December 2023. The cohort included 22 males and 14 females, with a mean age of 10.1±2.7 years (range: 4.3-14.3 years). Among them, 27 cases were primary tumor resections with post-resection bone defects of 17.4±3.2 cm (range: 13.5-25.0 cm), and 9 cases were revision surgeries. Preoperatively, femoral limb length discrepancy (LLD) was 29.6±14.3 mm (range: -1.2-55.0 mm), tibial LLD was 16.0±11.3 mm (range: -4.8-30.0 mm), and total lower limb LLD was 45.1±23.6 mm (range: -5.5-77.0 mm). The prosthesis was modular and compatible with existing tumor prosthesis components via taper connections. Lengthening was achieved by axial screw manual expansion through a 3-4 cm parapatellar arc incision, using a specialized wrench for adjustment. X-rays were performed pre-implantation, before and after each lengthening, and at the last follow-up to assess femoral, tibial, and total lower limb LLD, as well as extension length. At the final follow-up, limb function was assessed using the Musculoskeletal Tumor Society (MSTS)-93 score, and extension-related complications were analyzed.Results:All 36 children successfully underwent implantation and subsequent extension when indicated. The mean follow-up was 14.9±8.1 months (range: 6-31 months). Eleven patients underwent 16 lengthening procedures, with a mean of 1.5±0.8 per case (range: 1-3) and an average extension of 21.1±8.3 mm (range: 9.2-42.8 mm), achieving a total mean recovery of 31.0±16.1 mm (range: 10.4-61.7 mm). Two patients reached the maximum 5 cm extension capacity and underwent minor procedures to retract the extension device and secure the prosthesis. The remaining 25 patients did not require extension as their LLD was <2 cm. At the last follow-up, femoral, tibial, and total lower limb LLDs were 10.6±11.4 mm (range: -8.6-41.4 mm), 9.1±12.7 mm (range: -9.5-39.5 mm), and 20.1±21.0 mm (range: -10.4-72.5 mm), respectively. The mean MSTS-93 score for the 11 extended patients was 90.0%±12.7% (range: 80.0%-96.7%). Complications included two cases of aseptic loosening requiring revision, one transient peroneal nerve palsy after fixed-length filling, and three cases of prosthesis segment retraction due to excessive exercise. Retractions occurred at 9.1±3.3 months (range: 5.3-11.3 months) and were corrected during subsequent extensions without revision.Conclusions:Minimally invasive extendable prostheses allow individualized limb lengthening through small parapatellar incisions based on LLD and soft tissue tension. The extension mechanism is stable, and functional recovery is favorable.

Objective:To evaluate the preliminary clinical efficacy of minimally invasive extendable prostheses in limb-salvage treatment for distal femoral osteosarcoma in children.Methods:A retrospective analysis was conducted on 36 children who underwent reconstruction of bone defects after distal femoral osteosarcoma resection with minimally invasive extendable prostheses at Peking University People's Hospital between December 2021 and December 2023. The cohort included 22 males and 14 females, with a mean age of 10.1±2.7 years (range: 4.3-14.3 years). Among them, 27 cases were primary tumor resections with post-resection bone defects of 17.4±3.2 cm (range: 13.5-25.0 cm), and 9 cases were revision surgeries. Preoperatively, femoral limb length discrepancy (LLD) was 29.6±14.3 mm (range: -1.2-55.0 mm), tibial LLD was 16.0±11.3 mm (range: -4.8-30.0 mm), and total lower limb LLD was 45.1±23.6 mm (range: -5.5-77.0 mm). The prosthesis was modular and compatible with existing tumor prosthesis components via taper connections. Lengthening was achieved by axial screw manual expansion through a 3-4 cm parapatellar arc incision, using a specialized wrench for adjustment. X-rays were performed pre-implantation, before and after each lengthening, and at the last follow-up to assess femoral, tibial, and total lower limb LLD, as well as extension length. At the final follow-up, limb function was assessed using the Musculoskeletal Tumor Society (MSTS)-93 score, and extension-related complications were analyzed.Results:All 36 children successfully underwent implantation and subsequent extension when indicated. The mean follow-up was 14.9±8.1 months (range: 6-31 months). Eleven patients underwent 16 lengthening procedures, with a mean of 1.5±0.8 per case (range: 1-3) and an average extension of 21.1±8.3 mm (range: 9.2-42.8 mm), achieving a total mean recovery of 31.0±16.1 mm (range: 10.4-61.7 mm). Two patients reached the maximum 5 cm extension capacity and underwent minor procedures to retract the extension device and secure the prosthesis. The remaining 25 patients did not require extension as their LLD was <2 cm. At the last follow-up, femoral, tibial, and total lower limb LLDs were 10.6±11.4 mm (range: -8.6-41.4 mm), 9.1±12.7 mm (range: -9.5-39.5 mm), and 20.1±21.0 mm (range: -10.4-72.5 mm), respectively. The mean MSTS-93 score for the 11 extended patients was 90.0%±12.7% (range: 80.0%-96.7%). Complications included two cases of aseptic loosening requiring revision, one transient peroneal nerve palsy after fixed-length filling, and three cases of prosthesis segment retraction due to excessive exercise. Retractions occurred at 9.1±3.3 months (range: 5.3-11.3 months) and were corrected during subsequent extensions without revision.Conclusions:Minimally invasive extendable prostheses allow individualized limb lengthening through small parapatellar incisions based on LLD and soft tissue tension. The extension mechanism is stable, and functional recovery is favorable.