BackgroundReconstruction of the proximal tibia following resection of malignant bone tumors in pediatric patients is traditionally limited to osteoarticular allografts or endoprostheses. Endoprostheses typically require resection or disruption of the distal femoral physis, which can lead to a leg length discrepancy (LLD). We introduce a novel form of proximal tibia limb reconstruction using a Compress® tibia hemiarthroplasty, which spares the distal femoral physis. MethodsWe retrospectively reviewed 5 patients who underwent proximal tibia osteosarcoma resection and reconstruction with a custom Compress® proximal tibia hemiarthroplasty. Data on function, survival, LLD, complications, and patient reported outcomes were collected. ResultsMean age at resection was 10.4 years[range:8.8-12.9 years]. Mean implant survival was 59 months[range:34-83 months]. One patient developed a deep infection and two patients required implant lengthening. Both were later converted to a rotating hinged total knee arthroplasty(RHTKA) >58 months after index surgery. At last follow-up, all living patients had knee ROM from 0-110 degrees, walked unassisted, and had no LLD or knee instability. Mean TESS score was 90[range:80-97]. ConclusionProximal tibia hemiarthroplasty reconstruction after tumor resection in skeletally immature patients preserves the distal femoral physis, and may potentially reduce LLD and delay conversion to a RHTKA until after skeletal maturity. Level of EvidenceCase Series, level IV.