An anthropometric study of the distal ulna: implications for implant design.

Arthroplasty of the distal ulna is frequently used for distal radioulnar joint disorders; however, prosthetic failures are common. An implant replicating the ulna may be advantageous from the viewpoint of joint kinematics, wear, and fixation. The geometry of 40 distal ulnas was quantified by computed tomography scanning and radiography. Ulnar head diameter (16.8 +/- 1.6 mm), canal diameter (8.3 +/- 1.6 mm), eccentricity of the head relative to the shaft (2.5 +/- 1.4 mm), and angle of articulation (176 degrees +/- 29 degrees ) were measured. No correlation was found between the diameters of the ulnar head and intramedullary canal (R(2) = 0.2). A modular head-stem system with an eccentric offset may best reproduce the geometry of the distal ulna.