Three-dimensional measurement of proximal radioulnar space during active forearm pronation.

Distal biceps tendon ruptures have been reported to be associated with narrowing of the proximal radioulnar space. There have been no studies that three-dimensionally measured the distance between the bicipital tuberosity and the proximal ulna during active motion. The purpose of this study was to three-dimensionally measure the proximal radioulnar space during active forearm pronation in healthy subjects. Five healthy volunteers (10 forearms) were recruited for this study. They consisted of all males with a mean age of 37 years (range, 34-46 years). Lateral fluoroscopy of forearm rotation from maximum supination to maximum pronation was recorded for both forearms. Three-dimensional forearm kinematics were determined using model-image registration techniques with fluoroscopic images and CT-derived bone models, and the closest distance between the bicipital tuberosity and the proximal ulna was computed at each 30° increment of radial axial rotation relative to the distal humerus. The distance between the bicipital tuberosity and the proximal ulna decreased with pronation, reaching a minimum value at 90° of radial rotation (average 4.6 ± 1.3 mm), then increased with further rotation to maximum pronation (P = 0.004). The clearance between the proximal radioulnar space and the distal biceps tendon is very small (<1mm). Hypertrophy of the bicipital tuberosity or tendon can induce impingement and lead to tendon rupture.