BONE STRENGTH AND HISTOMORPHOMETRY OF THE DISTAL FEMUR

The ultimate bone strength of the distal femur was measured radially, by indentation testing, around the transepicondylar line in 3 mm depth steps up to 12 mm below the subchondral bone plate. Specimens from 10 cadavers were used. This orientation of specimens was chosen as a way to provide measurement in a more physiologic orientation for load bea ring and to standardize the assessment. Bone hardness declined sharply over the first 6 mm below the surface, tending to plateau at deeper l evels. Within the top 6 mm layer the lateral condyle was softer than b oth the medial condyle and the central patellofemoral area (P < .05), but at deeper levels it maintained greater hardness. Of the histomorph ometric parameters, those showing the greatest consistent correlation with hardness were bone volume fraction and trabecular separation. Whe n the tibiofemoral and patellofemoral compartments were compared it wa s found that for a given value of bone volume fraction, condylar bone is marginally harder than patellofemoral bone. The data are relevant t o the design of implants that match their geometric and material prope rties to the shape and strength of the underlying bone.