Subchondral bone density of the radial head measured with subtraction densitometry.

The purpose of this study was to develop a two-dimensional density distribution pattern of the subchondral cortical bone of the radial head using subtraction densitometry. The bone density of 32 normal specimens and five with macroscopic signs of osteoarthritis was measured before and after milling off the cortical bone surface. Electronic subtraction gave the density of the subchondral cortical bone. Twenty-one specimens had areas of high bone density in the ulnar-dorsal area, five specimens showed a ventral and ulnar density maximum and six had a density maximum in the center of the radial head joint surface. No density maximum was seen in the lateral part of the joint surface. The density maximum shifted towards the dorsal-ulnar part of the radial head with decreasing total subchondral bone density. Osteoarthritic radial heads had the same distribution as non-arthritic specimens. Eccentric subchondral bone density reflects eccentric radiohumeral force transmission. This could be a reason for development of radiohumeral arthritis or the failure of radial head prostheses. Bone density patterns correlate with the incidence of radial head fractures and fracture line may be positioned between areas of high and low densities.