Ulnomeniscal Homologue of the Wrist: Correlation of Anatomic and MR Imaging Findings

Abstract

To evaluate the anatomy of the ulnar side of the wrist in the region of the triangular fibrocartilage (TFC) complex, with special focus on the ulnomeniscal homologue (UMH) and its relationship to surrounding structures. Institutional review board approval and informed consent were not required. Ten upper extremities were harvested from the nonembalmed cadavers of four women and six men (age range at death, 56-97 years; mean age at death, 83 years) and used according to institutional guidelines. Magnetic resonance (MR) imaging and MR arthrography of the wrist were performed with the wrist in neutral position, maximal ulnar deviation, and maximal radial deviation by using intermediate-weighted sequences. The specimens were cut into 4-mm-thick sections that corresponded to the MR imaging planes. The gross anatomic features of the UMH and its relationship to adjacent structures were evaluated and compared with imaging findings. UMH variants, as described in previous articles on purely anatomic studies, were sought on MR images. MR findings of the wrist in neutral position were compared with those of the wrist in maximal ulnar and radial deviations. Histologic examination was used to further elucidate the structure of the UMH. The UMH displayed complex anatomic features because of its obliquely oriented course. However, it could be divided into styloid, radioulnar, and collateral components and a distal insertion. The UMH variants described in previously published studies could be identified, but evaluation results were highly dependent on the wrist position at imaging. The anatomy of the UMH is complex. For assessment of the UMH and the ulnar side of the TFC complex, coronal MR arthrography with the wrist in neutral position or radial deviation might be superior to standard MR imaging.