Skier's Thumb Workup

Updated: Feb 01, 2022
  • Author: Patrick M Foye, MD; Chief Editor: Sherwin SW Ho, MD  more...
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Laboratory Studies

Laboratory studies are not indicated for the diagnosis of skier's thumb.


Imaging Studies

Clinical examination of the thumb still remains the criterion standard in the diagnosis of a UCL rupture of the thumb. [14] If the diagnosis of skier's thumb is uncertain or if a concomitant fracture is suspected, additional diagnostic tools may be used, such as imaging studies. [14]

In a prospective study at a hospital in the Netherlands, Mahajan et al trained their resident physicians to perform physical examination techniques for skier’s thumb, including both inspection and stress testing at the involved joint. In 30 patients who had MRI confirmation of a skier’s thumb, the physician trainees were able to conclusively make the diagnosis in 73% of these cases. The authors concluded that imaging studies could be reserved for the 27% of patients with inconclusive physical examination findings. They noted that limitations to the physical examination included preexisting natural unilateral or bilateral UCL laxity, or acutely, swelling and bleeding. They also noted that physical examination would not be sufficient assessment for bony injury such as avulsion fracture at the UCL attachment site(s), and thus radiographs of the thumb are generally needed for that purpose. [15]

Plain radiographs of the thumb are first obtained to assess for possible thumb fracture or subluxation (see the images below). An avulsion fracture of the volar base of the proximal phalanx commonly accompanies UCL injuries. The thumb is considered dislocated when it is malrotated or displaced by more than 1 mm. [11]

Recent research describes the "sag sign" as a reliable indicator of thumb UCL underlying injury. The sag sign is volar subluxation of the proximal phalanx relative to the metacarpal at the MCP joint, evident on plain film. [16]

Anteroposterior radiograph displaying a gamekeeper Anteroposterior radiograph displaying a gamekeeper's fracture.
Lateral radiograph displaying a gamekeeper's fract Lateral radiograph displaying a gamekeeper's fracture.

Stress radiographs of the MCP joint are used to assess the severity of damage to the thumb and UCL. A joint opening that is greater than 30º while the MCP is fully flexed is consistent with complete rupture of the UCL; if the joint opening is less than 30°, one can assume that part of the ligament remains intact (see the image below). If questions arise regarding the degree of joint opening and the severity of damage, stress radiographs of the uninjured thumb can be obtained for comparison.

Radiograph displaying a stress test of a torn ulna Radiograph displaying a stress test of a torn ulnar collateral ligament.

One alternative to stress imaging of the MCP joint via radiographs is to perform the stress views via fluoroscopy. Fluoroscopy can provide the advantage of being able to observe and assess stress views in real time. Patel et al in their study of 100 non-symptomatic (non-injured) subjects sought to establish normative data for the use of fluoroscopy in assessing the anatomic structures involved in skier’s thumb. They noted in these non-symptomatic subjects that the fluoroscopic measurements would have essentially resulted in a false-positive diagnosis of skier's thumb in 1.5% or 3% of these individuals, respectively, depending on whether they used the criteria of stress angulation of greater than 30° or a left-versus-right difference in angulation of greater than 15°. Thus, fluoroscopic stress views could be very useful, with a low but notable rate of false-positives. [17]

Magnetic resonance imaging (MRI) is useful for evaluating UCL injuries, [18] but it is expensive and not always necessary. A study by Plancher et al showed that MRI has a greater than 90% sensitivity and a greater than 90% specificity for identifying UCL tears. [18]

Ultrasonography is less expensive than MRI. Shortly after presentation, ultrasonography yields higher positive predictive values than clinical examination for ruptures of the UCL. [19] Diagnostic musculoskeletal ultrasound can help to distinguish between full thickness versus partial thickness tear of the UCL. A partial thickness tear can show up on longitudinal views as a focal hypoechoic area with partial fiber disruption, typically close to the distal insertion of the UCL. Also, Doppler imaging studies may show hyperemia at the region of partial tear. Conversely, ultrasound findings with a full-thickness UCL tear can show retraction of the UCL where the retracted UCL appears as a hypoechoic mass-like structure. [20]  However, some discrepancies can be found in the medical literature as to whether ultrasonography is helpful [14, 21] or misleading [22, 23] in the diagnosis of a UCL injury.

Radiograph displaying a stress test of a torn ulna Radiograph displaying a stress test of a torn ulnar collateral ligament.