Effect of radial head malunion on radiocapitellar stability

Background: Management for Mason type II radial head fractures is controversial. We hypothesized that angulation or depression of a marginal radial head fragment would affect radiocapitellar stability similarly to fragment excision. Materials and methods: A Mason type II radial head fracture was created in 6 cadaveric elbows by excising a segment from the anterolateral quadrant that was 30% of the diameter of the articular surface. Radiocapitellar stability was recorded under 5 sets of conditions: (1) intact radial head (intact), (2) 30% surface area fragment resected (partially excised), (3) anatomic fragment fixation with screws (fixed), (4) fragment fixation with 2 mm of depression relative to the articular surface (depressed), and (5) fragment fixation after a 30° wedge resection (angulated). Results: The forces required to subluxate the joint were greatly reduced after fragment excision (5 ± 1 N; P = .0001) and restored to normal (21 ± 1 N; P = .9) after anatomic fixation of the excised fragment. The peak forces were significantly reduced with fragment depression (4 ± 1 N) and angulation (4 ± 2 N; P = .0001). Conclusion: A radial head fracture that is depressed 2 mm or angulated 30° may cause up to an 80% loss of concavity-compression stability of the radiocapitellar joint.