Kinematics of the ulna during pronation and supination in a cadaver study: implications for elbow arthroplasty.

Abstract

Aim of this study was to exactly describe and quantify kinematics of the ulna during pro- and supination. Biomechanical study in fresh frozen cadavers. A previous MRI study revealed a varus/valgus motion of the ulna averaging 7.1 degrees during pro-/supination. Axial rotation, however, could not be quantified. Sixteen arms were examined in a new apparatus that fixed the humerus on a template and allowed forearm rotation. Motion of a Kirschner wire placed in the ulna was recorded in steps of 30 degrees by two perpendicularly arranged charge coupled device cameras during pro- and supination. From supination to pronation the ulna showed a semi-lunar evasive motion in the coronal and transverse plane with an initial varus shift, then a dorsal and finally a valgus shift. Motion in the coronal plane averaged 14.14 degrees (SD 4.78). Valgus angles of the ulna in 30 degrees, 60 degrees and 90 degrees pronation were significant (P<0.05) to each other and the neutral position. Varus angles of the ulna in 30 degrees, 60 degrees and 90 degrees supination (P<0.01) were significant to each other and the neutral position.A maximum ulnar axial pronation rotation of 3.2 degrees (SD 2 degrees ) was noted. Axial rotation angles of 90 degrees and 60 degrees of pronation were significant to each other and to the neutral position (P<0.05), respectively. To prevent increased stress on the bone-cement interface in elbow arthroplasty, a mean axial rotation of at least 3.2 degrees should be possible.