Classification of diaphyseal tumors based on residual medullary cavity length for prosthetic reconstruction.

Diaphyseal prosthetic reconstruction for bone tumors continues to face challenges with failures due to the lack of evidence-based classification systems. This study aimed to develop and validate a novel classification framework to optimize reconstruction strategies through a retrospective analysis of 112 patients undergoing diaphyseal prosthetic reconstruction between 2010-2021. Diaphyseal tumors were classified into five types according to anatomical location and residual medullary cavity length, with each category corresponding to a tailored prosthetic reconstruction strategy. Clinical outcomes demonstrated a mean Musculoskeletal Tumor Society score of 24.3 ± 3.3 with comparable functional outcomes across classification types. The overall complication rate was 16.1% (18/112), primarily involving aseptic loosening (ASL, 8%) and structural failures (3.6%), with a reoperation rate of 6.3% (7/112). Notably, Type I reconstructions using standard stems without plates showed the highest complication rate (21%), while Type IIIa reconstructions exhibited no complications. Competing risk model analysis showed that cumulative mortality rates at 0.5, 1, 3, 5, and 8 years were 6.4%, 17.4%, 54.4%, 59.1%, and 66.5%, respectively, while cumulative complication rates were 2.7%, 6.5%, 12.5%, 19.4%, and 22.5%, respectively. These findings establish diaphyseal prostheses as effective solutions for intercalary defect reconstruction, emphasizing their role in facilitating early weight-bearing and functional recovery. The novel classification system for diaphyseal tumors provides valuable guidance for the design and application of prosthetic reconstructions.