SCIENTIFIC ARTICLE Articular Surface Area of the Coronoid Process and Radial Head in Elbow Extension: Surface Ratio in Cadavers and a Computed Tomography Study In Vivo Seong-Ho Shin, MD, In-Ho Jeon, MD, Hyo-Jin Kim, BS, Matthew McCullough, PhD, Jae-Hyuck Yi, MD, Hwan-Seong Cho, MD, Il-Hyung Park, MD 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 mea- sured 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. (J Hand Surg 2010;35A:1120 – 1125. © 2010 Published by Elsevier Inc. on behalf of the American Society for Surgery of the Hand.) Key words Articular surface area, coronoid process, osteoarthritis, radial head. T HE FUNCTIONING OF the elbow involves the com- plex movement of unique structures such as the distal humerus, coronoid process, and radial head. Flexion/extension of the elbow joint requires movement at the radiocapitellar joint as well as the ulnohumeral joint. Forearm rotation requires movement of the proximal and distal radioulnar joint as well as at the radiocapitellar joint. Degenerative changes in the cartilage of the elbow have been most commonly observed between the artic- ulation of the radial head and capitellum. 1 Several articles discuss biomechanical force trans- mission, pressure distribution, and articular cartilage wear patterns in the elbow joint. 2–6 Some of these From the Department of Orthopaedic Surgery, College of Medicine, Kyungpook National University Hospital, Daegu, Korea; Department of Physical Therapy, Daegu University, Daegu, Korea; Biomechanics & Motion Analysis Laboratory, Mayo Clinic, Rochester, MN; Department of Radiology, College of Medicine, Kyungpook National University Hospital, Daegu, Korea. Received for publication July 1, 2009; accepted in revised form April 2, 2010. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding authors: In-Ho Jeon, MD, and Il-Hyung Park, MD, Department of Orthopedic Sur- gery, Kyungpook National University Hospital, 50 Samduk 2, Chung-gu, Daegu, Korea, 700-721; e-mail: jeonchoi@chol.com. 0363-5023/10/35A07-0013$36.00/0 doi:10.1016/j.jhsa.2010.04.002 1120  ©  Published by Elsevier, Inc. on behalf of the ASSH.