Articular surface area of the coronoid process and radial head in elbow extension: surface ratio in cadavers and a computed tomography study in vivo.

PURPOSE: To quantify the articular surface area ratio of the radial head to the coronoid process to gain a better understanding of the stress distribution across these articulations and possibly to explain the patterns of osteoarthritis that are commonly seen in the elbow.

METHODS: Thirty cadaveric elbows were harvested and dissected to allow measurement of the radial head and coronoid process articular surfaces. The articular surface areas were measured using the Image J program (National Institutes of Health, Chicago, IL). Twelve men were recruited for this study, and all received a computed tomography (CT) scan of the elbow. A 3-dimensional image of the proximal radioulnar articular surface was created using volume rendering. All specimens were measured 3 times by 2 observers.

RESULTS: In the cadaveric measurements, the mean area of the radial head articular fossa was 247.3 +/- 52.6 mm(2) (mean +/- SD). The mean area of the medial facet of the coronoid process was 232.29 +/- 36.5 mm(2), and the mean area of the lateral facet was 141.9 +/- 33.3 mm(2). The articular surface area ratio of radial head to coronoid process was 1:1.5. In the CT measurement, the mean area of the radial head articular fossa was 258.9 +/- 26.3 mm(2). The mean area of the coronoid process articular surface was 376.9 +/- 37.0 mm(2). The articular surface area ratio of radial head to coronoid process was 1:1.46.

CONCLUSIONS: The ratio of articular surface area of radial head to coronoid process is 1:1.51 in cadavers and 1:1.46 using a CT in vivo, which is the reverse of the reported force transmission ratio across the elbow joint.