Three dimensional analysis of the fracture location of the radial head: comparison between simple radial head fracture and radial head fracture with complex elbow instability. Hypothesis: It is suggested that the anterolateral quadrant of the radial head with the forearm in neutral position is the most common location of fracture in Mason type 2 radial head fractures, but in some cases, fracture is observed in other quadrant, especially in the fracture with instability. Knowing the location of the fracture part in radial head is of paramount importance for planning the placement of implant for internal fixation. However, it is difficult to predict the exact location of the fracture before the internal fixation because the location can vary by the forearm rotation. The purpose of this study is to investigate the difference of the fracture location of Mason type 2 radial head fracture between simple radial head fracture and radial head fracture with complex elbow instability. Methods: From the 19 cases of Mason-type radial head fracture, three-dimensional computed tomography (CT) model was created. Along the axis made from the center of the radial head to the center of the radius at the biceps tuberosity level, corresponding point of the biceps tuberosity on the articular surface was defined as 0° point. Proximal articular surface was divided into a clock face of 360°. Fracture location was measured by the angle from the 0° point to the fracture line. The location of the start and end of the fracture was investigated and compared between the group with simple radial head fracture (group 1; n = 11) and the group with complex elbow instability (group 2; n = 8). Average start point, end point, and subtend of the fracture were evaluated using t test. Anterolateral quadrant was defined between 138° to 228°. Results: The average angle subtended by the fracture line was 143.8° (SD, 19.0) in all cases. The average start point of the fracture was 114.9° in group 1 (SD, 50.4; range, 29°-211°) and 108.8° in group 2 (SD, 30°; range, 75°-151°) (P = .763). The average end point of the fracture was 255.8° in group 1 (SD, 40.2°; range, 204°-327°) and 256.6°in group 2 (SD, 34.8°; range, 207°-302°) (P = .964). The average angle subtended by the fracture line was 140.9° in group 1 (SD, 21.1°; range, 116°-1T5°) and 14T.9° in group 2 (SD, 16.0°; range, 119°-172°) (P = .445). Summary: Location of the radial head fracture, using the biceps tuberosity as a standard was evaluated between the group with simple radial head fracture and the group with complex elbow instability. No difference of the fracture distribution was observed between the 2 groups. In both groups, fracture extended from the anterolateral quadrant to the anteromedial quadrant. Those findings can affect the approach and planning of the internal fixation of the radial head fracture.
