Motion analysis in two dimensions of radial-ulnar deviation of type I versus type II lunates

The motions of 2 different types of lunate (type I, no medial hamate facet; type II, medial hamate facet) were evaluated and compared during radial-ul nar deviation of the wrist using radiography and magnetic resonance imaging . Ten right wrists (5 type I and 5 type II lunates) were studied using post eroanterior and lateral x-rays. Six of the 10 normal volunteers (3 type and 3 type II lunates) were studied using magnetic resonance imaging in 6 posi tions of radial-ulnar deviation. In the radiographic study the ulnar shift ratio of the lunate (USR), the shortest distance between the proximal ulnar tip of the lunate and the distal ulnar edge of the sigmoid notch of the ra dius (R-L), the closest distance between the distal ulnar tip of the lunate and the proximal pole of the hamate (L-H), the radius of curvature of the proximal head of the capitate (Cr) on posteroanterior view, and the radiolu nate angle on lateral view were measured in each wrist in each of the 6 pos itions. There were statistically significant differences between type I and II lunates with regard to average maximum ulnar deviation of USR and R-L, total change of USR, R-L distance and L-H distance, average L-H distance an d Cr distance in all positions, and average radiolunate angle in neutral an d 15 degrees ulnar deviation. In the magnetic resonance imaging study the w rists with a type I lunate did not have contact between the lunate and hama te in any position; the wrists with a type II lunate did have contact betwe en the hamate and the lunate, but only in ulnar deviation. The results of t his study demonstrate that the kinematics of a type lunate are different fr om those of a type II lunate during radial-ulnar deviation of the wrist. (J Hand Surg 2000;25A:877-888. Copyright (C) 2000 by the American Society for Surgery of the Hand.).