What is the diagnosis?

This patient has a tear of the ulnar collateral ligament (UCL) of the thumb with an associated 1st proximal phalanx avulsion fracture.

Image 2:  AP plain film of the right hand showing an avulsion fracture at the ulnar corner at the base of proximal phalanx of the right thumb with associated displacement. (author’s own annotations) Case courtesy of Khalid Alhusseiny, Radiopaedia.org, rID: 166597. https://radiopaedia.org/cases/skiers-thumb-3?lang=us. 

• Pearl: This is known as gamekeeper’s thumb or skier’s thumb but can also be commonly seen in hockey, soccer, basketball, racquet sports, and breakdancers.

What is the mechanism of injury?

The mechanism of acute injury is hyper-abduction at the thumb MCP with the radial force spraining or tearing the UCL. [1

The UCL is one of the primary stabilizers for instances when valgus stress is applied to the thumb. It also serves a major function with gripping maneuvers. The UCL works in concert with the overlying adductor pollicis aponeurosis to provide dynamic stability. 

Image 3. Illustration of common mechanism of injury. Courtesy of Mount Siani Residency Blog 

Image 4. UCL rupture anatomy. Case courtesy of Frank Gaillard, Radiopaedia.org, rID: 7641

• Pearl: UCL injuries were initially described in 1955 as a chronic injury and instability of the MCP joint in Scottish gamekeepers. This was due to the repetitive valgus stressing of the UCL of the thumb in the motion used by gamekeepers to break the neck of rabbits. [3]

What are the expected physical exam findings?

The patient will present with pain and possible swelling over the ulnar aspect of the first MCP joint. There may be a palpable mass proximally which should raise suspicion for a Stener lesion. The pain is typically worse with pinching or gripping/grasping movements and may be associated with weakness. [2] 

• Pearl: A Stener lesion is when the torn end of the UCL moves superficially to the adductor aponeurosis and is a concerning finding as it can prevent healing without surgery. [4] 

Image 4: Stenner lesion anatomy. Case courtesy of Frank Gaillard, Radiopaedia.org, rID: 7641

In order to examine UCL stability, it is best to examine the unaffected side first. Valgus stress test is performed by holding the thumb proximally to the MCP joint to minimize rotation and applying radial stress. This should be done in both full extension and 30 degrees of flexion to evaluate for endpoint as well as metacarpal-phalangeal deviation. [3] The laxity for a positive stress test has been described as 30 degree overall or a 15 degree difference from the contralateral thumb, however most hand surgeons place more weight on the endpoint. [5]

• Pearl: If the physical exam is limited by pain, swelling, or muscle spasm, local anesthetic may be helpful in making the diagnosis and evaluating for a complete tear.

• Pearl: some clinicians harbor concern about creating a Stenner lesion by stressing the UCL during an exam. If the initial injury didn’t have enough force or the proper vectors to cause a Stenner lesion, the force of our exam should not cause one either. [1]

What imaging should you get?

Imaging is recommended to evaluate for displaced fractures of the metacarpal or proximal phalanx and to evaluate for a Stener lesion. First line imaging is plain radiographs with AP, lateral, and oblique views. Stress views can be considered to aid in diagnosis but these are controversial as they are difficult to standardize and interpret, not to mention likely limited by patient discomfort. [1]

Ultrasound is helpful in evaluating the UCL fibers as well in identifying a Stener lesion, especially during dynamic imaging. [4] However, the best imaging to evaluate for Stener’s lesion is an MRI. 

Image 5-9: ultrasound images showing UCL rupture and a Stenner lesion. Case courtesy of Maulik S Patel, Radiopaedia.org, rID: 53870

• Pearl: Children more commonly present with a Salter-Harris III avulsion at the UCL insertion rather than a true UCL rupture due to their immature skeleton. [1]

What is the management in an urgent setting? When do you consult orthopedic surgery?

If the patient has a partial UCL tear, they should be placed in a thumb spica splint or cast for MCP immobilization for 4-6 weeks and then begin grip and pinch strengthening exercises with physical therapy.

Orthopedic surgery should be consulted for a complete tear and displaced avulsion injury. Even with a complete tear, surgical intervention has an excellent prognosis for return to sport. [2, 5]