DISTAL RADIUS FRACTURES - MECHANISMS OF INJURY AND STRENGTH PREDICTION BY BONE-MINERAL ASSESSMENT

The strength of the radius depends on the mechanical properties of can cellous and cortical bone. By assessing both compartments quantitative ly with bone densitometry, we tried to identify the specificity of eac h in predicting the load at which the distal radius will fracture. Twe nty human cadaver forearms were scanned for bone mineral and geometric properties with quantitative computed tomography and dual x-ray absor ptiometry. In both a neutral loading situation and one in which the wr ist was extended 45 degrees, the load distribution was determined with pressure-sensitive films and a fracture simulating a fall on the hand was produced with a material testing machine. Fractures that occur wi th the wrist in extension were produced by a central impact of the sca phoid onto the radiocarpal joint, and those that occur under neutral l oading conditions were produced by a more commonly distributed loading pattern. The load at fracture was most specifically predicted (r(2) = 0.74) by bone mineral and geometric measures of the cortex at the sha ft of the radius. Bone mineral density measures of trabecular (r(2) = 0.64) and total (r(2) = 0.66) bone were less successful in predicting the fracture load. After adjustment for bone sizer the geometric and d ensity measures revealed similar specificity. Cortical bone, therefore , contributes significantly to the strength of the distal radius and m ay play an important role in the prediction of osteoporotic wrist frac tures.