• Christine C Johnson, Susanne Roberts, Douglas Mintz, Peter D Fabricant, Robert N Hotchkiss, and Aaron Daluiski.
• Hospital for Special Surgery, New York, NY.
• J Hand Surg Am. 2018 Nov 1; 43 (11): 1039.e1-1039.e7.

PurposeThe location of capitellar osteochondritis dissecans (OCD) lesions in the sagittal plane guides the surgical approach, and lesion location in the coronal plane influences surgical management. Although most lesions have been reported to occur between 4 o'clock and 4:30 (120° to 135° anterior to the humerus), some lesions are located elsewhere in the capitellum. The primary aim was to define the region of the capitellum affected by OCD lesions using a novel clock-face localization system.MethodsWe reviewed 104 magnetic resonance imaging examinations diagnosing a nontraumatic capitellar OCD lesion. In the sagittal plane, lesion margins were recorded as degrees on the capitellum and converted into a clock-face format in which 0° corresponds to 12:00 with the forearm facing to the right. The 0° axis (12-o'clock axis) was defined as a line parallel to the anterior humeral line that intersects the capitellum center. The following coronal measurements were recorded: lesion width, capitellar width, and distance between the lateral capitellum and lateral lesion. Two independent observers took measurements.ResultsIn the sagittal plane, average lesion location was 92° to 150° (3:04-5:00, clock face) and ranged from 52.1° to 249.5° (1:44-8:19, clock face). Average lesion dimensions were 10.7 mm (mediolateral width) and 5.2 mm (anteroposterior depth). Interrater reliability was high (intraclass correlation coefficient = 0.98).ConclusionsUsing a magnetic resonance imaging-based clock-face localization system, we found that capitellar OCD lesions affect a broad region of the capitellum in the sagittal plane.Clinical RelevanceThe clock-face localization system allows for precise description of capitellar OCD lesion location, which may facilitate intraoperative decision and longitudinal monitoring.Copyright © 2018 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

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