Aim of the study: To define the dimensions of the radial head, as well as the radiocapitellar and proximal radio-ulnar joints. The most congruent portions of the radial head articulations were determined.

Materials & Methods: Computed tomography scans of twenty-two cadaveric adult elbows were obtained in three forearm positions – supination, neutral, pronation. The radial head dimensions, the radiocapitellar joints, and the proximal radioulnar joints were also measured. Multivariate analysis of variance was used to determine which portions of each articulation were the most congruent.

Results: At the level of the radial trough, the maximum diameter was 22.3 mm, the minimum diameter was 20.9 mm, and the diameter difference was 1.4 mm. This difference represented only 6.3% of the overall maximum diameter. The depth of curvature of the radial head trough was 2.3 mm, the radial head length was 9.8 mm, and the radial neck length was 10.7 mm. At the isthmus of medullary canal, the maximum diameter was 9.7 mm, the minimum diameter was 8.2 mm, and the diameter difference was 1.5 mm. This difference represented 15.6% of the maximum diameter. The average radiocapitellar distance at the radial lip was 4.0 mm, the trough 2.4 mm, and the ulnar lip 2.2 mm. Thus, the radial head tended to become uncovered at the radial lip (p < 0.0001). The radiocapitellar joint was tighter in pronation than in supination (p = 0.0008). The proximal radioulnar joint was most congruent at the MPRUJ (middle proximal radioulnar joint), at the midportion and posterior aspects, rather than the anterior aspect (p < 0.0001). The PRUJ coverage was between 69.0 and 79.2 degrees.

Conclusions: Prosthesis trial sizing should be judged by the articulations providing the most congruency –

1) the ulnar lip or trough of the radiocapitellar joint in pronation and

Aims: The purpose of this study was to evaluate the incidence of combined osseous and ligamentous injuries by MRI in patients admitted with displaced or comminuted radial head fractures. Methods: A retrospective study was undertaken on twenty-four consecutive patients with an acute radial head fracture (Mason type II & III) without documented dislocation or tenderness at the distal radioulnar joint (DRUJ). The evaluation was done with elbow antero-posterior and lateral x-ray images and MRI images performed with the patient in a splint in sagittal, coronal, axial, axial oblique and coronal oblique planes. We investigated the integrity of both medial and lateral collateral ligaments, the presence of capitellar osteochondral defects or bone bruises and loose bodies. Results: The MRI evaluation of the participants in this study revealed the presence of a high percentage of ligamentous injuries. The incidence of associated injuries was: medial collateral ligament not intact: 13/24 (54.16%), lateral collateral ligament not intact: 18/24 (80.1%), both collateral ligaments not intact: 12/24 (50%), capitellar osteochondral defects 7/24 (52.4%), capitellar bone bruises 23/24 (95.83%) and loose bodies 22/24 (91.67%). Conclusions: High level of suspicion should be employed when treating displaced or comminuted radial fractures because concurrent osseous and/or ligamentous injuries might be present This speciþc type of injury with the broad range of presentation and accompanying injuries tests the clinician and makes the treatment challenging.