Imaging description

Skier’s thumb (also known as Gamekeeper’s thumb) is a rupture of the ulnar collateral ligament (UCL) at the first metacarpophalangeal joint. The lesion is not readily visible on radiography unless there is an associated avulsion fracture at the ulnar-sided base of the first metacarpal (Figure 38.1). The soft tissue injury can be seen by MRI as a rupture of the UCL. The Stener lesion is when the ruptured UCL becomes displaced superficial to the adductor policis aponeurosis. On MRI a Stener lesion is seen when the ruptured UCL is seen superficial to the aponeurosis or when the yo-yo on a string sign is seen on MRI. The yo-yo on a string sign is caused by the ruptured distal end of the UCL being doubled back upon itself (Figure 38.2). In general, radiographic stress views of the first metacarpophalangeal joint are not currently recommended to aid in the diagnosis of a Stener lesion or skier’s thumb.

Importance

Identification of a displaced avulsion fragment associated with a skier’s thumb is important to identify. When this fragment is displaced, it usually will need to be treated surgically or with fixation to promote healing.

Typical clinical scenario

A 24-year-old male has sustained a “ski pole” injury to his right thumb. There is swelling and tenderness at the UCL of the first metacarpophalangeal joint. The physical exam is positive for rupture of the UCL. A radiograph is ordered usually to rule out an underlying avulsion fracture. If the physical exam is positive for a Stener lesion, an MRI may be ordered for preoperative planning based on the surgeon’s preference.

Teaching point

In the clinical setting of a skier’s thumb injury, a radiograph is usually ordered to rule out an associated fracture. Any significant displacement of the fracture fragment will usually result in fixation in addition to immobilization. Physical exam (sensitivity around 95%) has been reported to be as sensitive as or more sensitive than MRI or US in diagnosing a Stener lesion (sensitivity ranges from 75% to upper 90th percentile range). When an MRI is requested for preoperative planning, one should carefully look for superficial displacement of the torn UCL or the yo-yo on a string sign to confirm the physical exam diagnosis. One should also carefully evaluate for other unsuspected injuries that might be visualized by the MRI.