Physeal-sparing distal femur megaprothesis for skeletally immature patients with osteosarcoma / 中华骨科杂志

ABSTRACT

Objective:To evaluate the clinical outcome of a special physeal sparing knee prosthesis for pediatric distal femoral osteosarcoma regarding the functional outcome, retention of the growth potential of the proximal tibia, and postoperative complications.Methods:A retrospective study was conducted to review 37 pediatric patients with osteosarcoma of distal femur who were treated in a single musculuskeletal tumor center between August 2015 and January 2019. Among them, 21 were boys and 16 were girls, aged from 5 to 12 years at the time of operation, with an average age of 9.1±2.1 years and the height of 115 to 160 cm, with an average of 140±10 cm. Tumor resection of distal femur was performed and the bone defect was reconstructed by a special hinged knee prosthesis which can preserve the proximal tibial epiphyseal plate. Demographic data was recorded. Overall leg length and tibial length was assessed by full-length standing anteroposterior radiographs of bilateral lower extremity with the patella pointing anteriorly preoperativelly and postoperativelly at each follow up. And the growth potential of the affected proximal tibia was calculated by comparing with the preoperative length of tibia. Meanwhile, the functional outcome was assessed by using the Musculoskeletal Tumor Society (MSTS) system, and the postoperative complications were analysed.Results:All patients underwent the tumor resection and reconstruction operation successfully. The average operation duration was 143±41 minutes, ranging 90 to 250 minutes. The average intraoperative blood loss was 314±397 ml, ranging 30 to 2 200 ml. The patients were followed up for 24 to 64 months, averaging 42.3±12.1 months. The postoperative knee range of motion was 100-130 degrees, with an average of 115.6±7.2 degrees. The postoperative MSTS score was 23-30, with an average of 26.7±1.6. To the last follow-up, the limb length discrepancy of the lower limb was 1.3 to 10 cm, and the length of the tibia was shortened from 0 to 3.8 cm compared with the opposite side, with an average of 1.3±1.0 cm. The growth percentage of the proximal tibial epiphysis on the affected side was 30% to 100%, with an average of 70%±17%. Totally, 13 patients suffered postoperative complication, the overall incidence of complications was 35% (13/37), and prosthesis-related complications were 16% (6/37). Three patients with wound dehiscence were managed by debridement and antibiotics. Radiographs revealed femoral stem loosening in a single patient 3 years after the initial operation and then the prosthesis was converted to an adult tumor knee endoprosthesis. Two cases experienced breakage of the femoral stem at 30 and 33 months, respectively, due to an accidental injury. They received revision surgery, and a new femoral prosthesis component was replaced. One patient developed femoral stem breakage at 10 months after surgery due to fatigue fracture, which treated with revision surgery. Tumor recurrence occurred in 6 patients. Among them, tumor recurrence in soft tissue occurred in 4 patients, and treated with regional resection without further recurrence. The other 2 patients experienced tumor recurrence at the distal femoral site, and treated with resection and prosthetic revision.Conclusion:The physeal sparing pediatric knee prosthesis can preserve the growth potential of the proximal tibial epiphyseal plate with good postoperative function and low incidence of prosthesis complications. Therefore, it can be an alternativeespecially for skeletally immature patients with distal femur osteosarcoma.