Ulnar collateral ligament.

An AP radiograph of the thumb demonstrates a nondisplaced avulsion fracture at the ulnar aspect of the base of the proximal phalanx (arrow). Fractures in this position cannot be safely assumed to represent the location of the distal end of the UCL. This finding does not exclude the presence of a displaced complete UCL tear or Stener lesion.

Consecutive fat-suppressed coronal T2-weighted images in a 16 year-old male following an injury to the thumb during football practice. Edema is demonstrated within the adductor pollicis muscle (asterisk) adjacent to the site of attachment at the volar aspect of the proximal phalanx (left). The middle image is one slice dorsal and demonstrates fibers of the UCL that are attached at the proximal phalanx (arrowhead). One slice further dorsal (right) demonstrates a tear of the dorsal fibers of the UCL insertion (arrow) compatible with a partial tear.

A 17 year-old male injured his thumb playing basketball 4 days prior to the MRI scan. Consecutive STIR coronals along the volar 1/3 of the MPJ demonstrate a minimally displaced complete tear of the UCL.

Consecutive coronal STIR images in a 49 year-old female with recent thumb injury from a fall and physical exam findings suspicious for a Stener lesion demonstrate a minimally displaced complete tear of the UCL at the metacarpal origin (arrow).

MRI is the advanced imaging modality that has met with the most success in evaluating UCL tears.22,23,24 Careful attention to proper positioning is vital to diagnosing and characterizing UCL tears (Fig. 6). Coronal images are most helpful in evaluating the UCL.  Axial images are most useful in identifying or confirming Stener lesions. Small deviations in alignment, especially on coronal series, can lead to false negative examinations.

The proper coronal plane for evaluating the thumb metacarpophalangeal joint should parallel the dorsal cortex of the metacarpal head (left)(green line). At this level the metacarpal head is rectangular or trapezoidal in contour. The next distal cut typically includes the sesamoids(right), which can be used as a landmark for planning with the coronal plane parallel to the plane of the 2 sesamoids. Sagittal images are perpendicular to the coronal image plane.



Reference