Lateral lunate morphology: an x-ray study.

The lunate has been described by Kauer as being thinner dorsally than volarly when measured proximal to distal. We used an x-ray method to measure the shape of the lunate in order to compare dorsal and volar thicknesses after recognizing clinically a group of patients with scapholunate dissociation in whom volar flexed lunates were present. Using this method, 292 standard lateral views of the lunate were collected randomly and measured. The shape of the lunate could be classified into 3 types: type D lunates have a thinner dorsal segment and correspond to Kauer's description; type V lunates have a thinner volar segment; type N lunates have equal dorsal and volar segments. There were 196 type D lunates (67%), 67 type V lunates (23%), and 29 type N lunates (10%). The radiolunate angles were measured in a random selection from type D and type V lunates to determine any relationship between the volar segment to dorsal segment thickness (wedge) ratio. No relationship within these groups was identified. However, there was a significant difference in the radiolunate angles between these two groups. Recognition of the prevalence of the type V lunate alters concepts proposed by Kauer and warrants further investigation of factors influencing lunate position.