Objective: To develop a schematic segmentation of the proximal ulna in order to detect, assess the frequency, and characterize the bony outgrowths arising from the trochlea and from the radial notch of the ulna, to enable differentiation of osteophytes from enthesophytes. Materials and methods: Eighty well-preserved ulna specimens from the collection of the San Diego Museum of Man were analyzed by two musculoskeletal radiologists. The trochlea and the radial notch of the ulna simulate the shape of a clock quadrant. The proximal ulna was divided into 24 anatomic areas. The relationships of the joint capsule and insertions of tendons and ligaments onto these area were assessed by the two readers, and the resulting appearances of bony outgrowths were compared at visual inspection and on Radiographs. Results: The interobserver visual comparison was good in 17 areas out of 24, but poor correlation was found in 7 areas. In one case, difficulties in differentiating osteophytes originating from the brachialis muscle/ tendon (area 9) from an enthesophyte originating from the capsule insertion on the coronoid process (areas 2 or 3) occurredand between two different enthesophytes in a further case. Five cases had difficulties in defining differences in the grading system of the outgrowths. The percentage of outgrowths observed in each of the areas was globally high, especially in areas 9 and 10. On radiographs it was possible to observe irregularities in ten areas; in eight at a threshold of height of 2 mm (areas 1-4, 9, 10, 11, 14) and in two at a threshold of height of 3 mm (areas 5, 6). The two readers had the same difficulties in differentiating enthesophytes from osteophytes at radiographic and visual examination. Conclusion: Our segmentation scheme is reproducible and objective, and permitted the differentiation of the bony outgrowths arising from the proximal ulna into osteophytes and enthesophytes, which may be particularly useful for the in vivo assessment of abnormalities seen in elbow overuse syndromes.
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