ulnomeniscal homologue

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The ulnomeniscal homologue (UMH) is an obliquely oriented, fibrocartilaginous structure, that forms part of the ulnar collateral ligament complex (ULC) of the wrist.

Gross anatomy

The UMH is located between the ulnar styloid process and the triquetrum. It adheres to the ulnar joint capsule and merges with the ulnar collateral ligament and the sheath of the extensor carpi ulnaris (ECU) tendon. These structures normally cannot be differentiated by imaging. Dorsally, the UMH inserts into the radial notch together with the dorsal radioulnar ligament .

From proximal to distal, the UMH can be divided into four components:

  • styloid
  • radioulnar
  • collateral
  • distal insertion

The styloid component is the principal part, it has triangular shape on coronal sections. The other parts serve as a suspension system, that attaches to the styloid process proximally, and the triquetrum and hamatum distally.

The UMH is separated from the TFC by the prestyloid recess of the wrist joint.

There are three variants of this recess :

  • wide opening
  • narrow opening
  • absent

Radiographic features

Ultrasound

The meniscal homologue can be visualized on ultrasound with the transducer placed at the dorsal ulnar aspect of the wrist in the longitudinal plane. The meniscal homologue is displayed as an echogenic structure adjacent to the triangular fibrocartilage disc, deep to the overlying ulnar collateral ligament of the wrist and the extensor carpi ulnaris tendon .

MRI

MRI is the method of choice for depicting the ULC. As with fibrocartilage in other parts of the body, it normally appears hypo-intense on T1- and T2-weighted images. As in the TFCC, there is a more signal intense, central ulnar portion due to fibro-vascular connective tissue. Assessment of the UMH and the prestyloid recess is only possible in the presence of effusion or intra-articular contrast (MR-arthrography). The appearance of this recess is highly dependent on the wrist position at imaging: if present, it collapses on ulnar abduction.

Related pathology

An ulnar detachment injury of the UMH has been described at arthroscopy . However, this has never been documented with MRI or MR arthrography.