Ulnar variance and the shape of the lunate bone. A radiological investigation.

The authors designed a study to test the hypothesis that the length of the ulna might affect the shape of the lunate bone because of long-term molding during life. This might then be useful to predict the presence or absence of a dynamic or static ulna plus by the shape of the lunate bone. In a prospective study, posterior-anterior wrist x-rays were taken in a standard fashion in 68 patients with a mean age of 34.5 years. Dominance, grip strength, ulnar variance and the shape of the lunate were recorded. Lunate shape, type 1, which is the least molded, was seen most frequently on both the left and right side and did not correlate with the dominant side. The most molded, type 3, was seen less frequently and almost exclusively on the nondominant side. No correlation was found between dynamic ulna plus and the type 3 lunate. Following statistical analysis, no correlation between ulnar variance and lunate shape was found, indicating that the shape of the lunate bone had no predictive value for predicting the presence or absence of a dynamic ulna plus variance. The hypothesis that the length of the ulna might influence the ultimate shape of the lunate could not be demonstrated.