Thumb Joint Fusion

UCL Injury to the MP Joint of the Thumb

An injury to the first MP joint can easily be overlooked in traumatic falls. The injuries to the collateral ligaments and subsequent dislocations can initially appear normal on x-ray. The patient usually describes a mechanism that consists of a sudden valgus force being applied to the MP joint of the thumb. This mechanism may cause disruption of the UCL, and if the joint is left unstable and untreated, a skier's thumb leads to early degenerative joint disease of the first MP joint (Fig. 51—5).

The incidence of UCL injuries ranges from 35 to 80% of all upper extremity injuries, and is presently the most common upper extremity injury in snow skiing. The most common site of the UCL disruption is at its origin or insertion; however, midsubstance or proximal tears are also possible. Other injuries to the MP joint of the thumb to be aware of are avulsion fractures, dorsal capsular tears of the MP joint, and volar plate injuries.

In 1962, Stener described the interposition of the UCL caught and retracted between the bone and adductor aponeurosis. When the UCL ruptures, a tender palpable

Adductor Insertion Avulsion Syndrome
Figure 51—5. (A) Instability seen in holding a pen in a 70-year-old with a chronic UCL injury. (B) Stress test of a chronic UCL untreated. (C) Fusion of a metacarpophalangeal (MP) joint of the thumb after failed identification of a UCL injury.
Chronic Instability Thumb
Figure 51—6. Palpable mass on physical exam noted over UCL of Figure 51—7. Orthoplast splint constructed by a hand therapist. the MP joint of the thumb.

prominence may be noted over the ulnar aspect of the MCP (Fig. 51—6). Heyman et al determined that an MP palpable mass was 100% sensitive for the diagnosis of a Stener lesion, but only 46% specific in a prospective clinical study. Determining if a soft or firm end point is present is essential in the diagnosis and grading of UCL tears. This part of the physical exam must be coupled with other tests, such as stress radiographs and an MRI, if necessary, to have the most accurate and specific diagnosis.

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