Clinical history: 28 year-old female who fell while skiing. An inversion recovery coronal image centered at the thumb metacarpophalangeal joint is provided. What is your diagnosis?
1a Figure 1: An inversion recovery coronal image centered at the thumb metacarpophalangeal joint
Findings
2a
Figure 2:
(2a) The coronal image demonstrates edema and a gap (arrow) at the distal attachment of the ulnar collateral ligament at the thumb metacarpophalangeal.
Diagnosis
Acute ulnar collateral ligament tear at the thumb metacarpophalangeal joint.
Discussion
The ulnar collateral ligament (UCL) of the metacarpophalangeal joint (MCP) of the thumb is injured when a valgus force is applied to an abducted thumb. This injury may lead to a painful, osteoarthritic, and chronically unstable joint if not properly evaluated and treated.
Acute UCL injuries usually occur from a fall on an outstretched hand with the thumb abducted. This mechanism is especially common among skiers who fall while gripping the ski pole and has been coined ‘skiers thumb”.1 “Gamekeeper’s thumb” originally referred to a chronic injury of the UCL of the thumb MCP from repetitive stresses. This condition was originally described in Scottish gamekeepers as an occupational hazard. Repetitive valgus forces at the thumb MCP occurred in the gamekeepers from wringing the necks of wounded rabbits.2 Gamekeeper’s thumb, as used today, refers to any acute or chronic injury of the UCL of the thumb MCP.
The UCL is most commonly injured distally at either the proximal phalangeal attachment or its midsubstance (Figure 3a, B). An avulsed fragment of bone may be visible on plain film in up to a third of cases . Pinch or passive stress views may be helpful in demonstrating instability associated with a deficient UCL, but may require local anesthetic for accurate assessment. Sprains and partial tears are often treated conservatively and are readily differentiated from complete UCL tears by MRI.
3a
Figure 3:
(3a) Dorsal renderings of the thumb MC joint demonstrating normal anatomy (A), torn nondisplaced UCL (B), and a Stener lesion (C). Ulnar collateral ligament (white arrow), adductor aponeurosis (arrowhead) are indicated.
Complete tears of the ulnar collateral ligament require prompt surgery. In general, the best functional results are obtained if surgical correction is achieved within 3 weeks of the injury. The longer corrective therapy is postponed, the poorer the outcome. In a subset of patients, the completely torn UCL becomes displaced proximal and superficial to the adductor pollicis aponeurosis. The interposed aponeurosis prevents apposition of the torn UCL to its normal site of insertion at the proximal phalanx. This injury is known as the Stener lesion (Figure3a, C) and has been described as a complication of complete UCL tears, with a frequency ranging from 33% to 80%.3 The clinical diagnosis of a complete UCL tear and the Stener lesion may be difficult. In some patients with a complete UCL tear, muscle spasm and edema can mask clinical instability at the MCP. In addition, although palpation of the displaced UCL as a knot along the ulnar aspect of the thumb MCP is presumptive evidence of a Stener lesion, this clinical finding is not always present. In these patients, MRI is a valuable tool for assessing the integrity of the UCL, enabling a prompt diagnosis.
4a
Figure 4:
(4a) A coronal proton density weighted image of a Stener lesion demonstrates the torn and retracted ulnar collateral ligament (arrow). The adductor aponeurosis (arrowhead) blocks the apposition of the torn end of the UCL to its normal site of attachment.
Conclusion
Gamekeeper’s thumb refers to injury of the UCL of the thumb MCP and is a serious, often subtle injury which requires prompt, accurate diagnosis to ensure an optimal outcome. MRI provides effective diagnosis and presurgical planning by accurately depicting the extent and chronicity of the UCL injury. MRI can easily differentiate sprains and partial tears from complete UCL tears and is invaluable in the diagnosis of the Stener lesion, which may be missed clinically.
References
1 Gerber C, Senn E, Matter P: Skier’s thumb. Surgical treatment of recent injuries to the ulnar collateral ligament of the thumb’s metacarpophalangeal joint. Am J Sports Med 1981 May-Jun; 9(3): 171-7.
2 Campbell CS: Gamekeeper’s thumb. J Bone Joint Surg Am 1955; 37(B): 148-9.
3 Louis DS, Huebner JJ, Hankin FM: Rupture and displacement of the ulnar collateral ligament of the metacarpophalangeal joint of the thumb. Preoperative diagnosis. J Bone Joint Surg Am 1986 Dec; 68(9): 1320-6.