Role of mechanical loading in healing of massive bone autografts

We assessed healing of a 3.5 cm autograft transport segment, denuded of periosteum, and docked to the healthy distal femur with an intramedullary nail. We hypothesized that healing relates to proximity to the healthy distal femur and to mechanical loading patterns. Total bone area, area of new bone apposition, and quality of new bone formed in the 2 weeks after surgery, and area and degree of perfusion 16 weeks after surgery were measured as a function of proximity and loading patterns (as defined by the major and minor centroidal axes, CA). At 16 weeks, no significant differences in early bone apposition or perfusion were observed as a function of distance from the healthy distal femur. Qualitatively, bone was well perfused, both vascularly and pericellularly, and highly remodeled. When cross-sections were pooled from distal to proximal through the docking zone and normalized for total bone area, significant differences in the amount of early proliferative woven bone were related to loading patterns. In contrast, no differences in normalized perfusion area were attributable to loading patterns. Furthermore, early bone apposition and perfusion decreased with increasing radial distance from the bone surface toward the intramedullary nail. Finally, no differences were observed in areas of resorption within the docking zone compared to baseline levels measured in the control (in bone removed to create the defect zone at the time of surgery). Interestingly, infilling of resorption spaces within docking zone specimens related significantly to predominant loading patterns, where areas within the major CA exhibited significantly more infilling.