The ulnar interosseous tuberosity exists: a radiological and descriptive cadaveric study.

PURPOSE: The anatomy of the ulna seems to have already been described exhaustively, particularly at its extremities, but very little in its middle third. We report the existence of an interosseous tuberosity on the interosseous border of the ulnar shaft that we have named the "tuberositas interossea ulnarii" (TIU). METHODS: First, we analyzed all side view X-rays of the forearm in neutral rotation, as well as forearm CT scans carried out during a 1-year period in our hospital. On these radiographic examinations, we evaluated the presence or absence of the TIU, its length, the thickness of the interosseous cortex at its level, above and below compared with anterior, posterior, and lateral bone cortices. In the second part of the study, we dissected cadaveric forearms to determine which ligaments and muscles were attached to it. RESULTS: A total of 91 standard forearm radiographs and 13 CT scans were analyzed. In all cases, the ulnar interosseous tuberosity was present. The mean tuberosity length was 107.5 mm (± 18.2), without any significant gender influence. It corresponded to a thickening (6.9 mm then 4.6 mm above and 3.9 mm below; p < 0.0001) of the ulnar interosseous cortex. Then, ten anatomic subjects (six females, four males) were dissected. We observed that this tuberosity served as an attachment for the central band of the interosseous membrane, for the deep flexor and extensor muscles for the long fingers, and for the abductor pollicis longus muscle's inner attachment. CONCLUSION: Tuberositas interossea ulnarii exists besides the tuberositas interossea radii, corresponds to thickening of the cortex and may play a role in the stability of the forearm and the function of the long fingers.