Ulnar Collateral Ligament Injury

Etiology

When the thumb is placed in extreme abduction or extreme hyperextension, there is a risk of injury to the ulnar collateral ligament, which stabilizes the base of the thumb at the first metacarpophalangeal joint.  In one specific group, skiers, this injury is more frequently observed since individuals can fall and strike their thumb on a fixed ski pole.[2] The role of the ulnar collateral ligament is to assist in the stability of the thumb near its base as it meets the first metacarpal. Any mechanism such as a fall or strike injury that forces the thumb to become forcefully abducted can threaten the integrity of the ulnar collateral ligament. Also, if the patient experiences repetitive injury through abduction at the thumb, chronic ulnar collateral injury pattern may result.[4][5]

Epidemiology

Ulnar collateral ligament injuries are observed more frequently in the male population, with a 60% predominance in this gender.[6] Specific patient populations that may be at risk include certain sporting activities where the mechanism of injury may occur, including, but not limited to, skiing, baseball, and javelin. Furthermore, simple mechanisms such as falls in the elderly may result in this injury pattern.

Pathophysiology

The anatomic function of the thumb is complex and beyond the scope of this article; however, it is important to recognize that the ulnar collateral ligament assists in stabilizing the thumb at the metacarpophalangeal joint. To adequately grasp and hold onto objects, the thumb acts in a coordinated fashion with hand muscles, finger muscles, and ligamentous structures, including the ulnar collateral ligament. By understanding this mechanism of thumb function, one can see how hyperextension (or extreme abduction) may result in a tear to the ulnar collateral ligament.  These can be classified as partial, complete, or chronic. As observed in other acute joint injuries, the patient may have swelling and tenderness at the first metacarpophalangeal joint. Also, there may be instability or laxity noted at that joint.[7]

History and Physical

The typical history obtained in a patient with ulnar collateral ligament injury includes fall or injury, causing extreme thumb abduction or hyperextension. The patient with localized discomfort to the first metacarpophalangeal joint area. Accompanied with the pain, there may be concomitant swelling near or at the thumb base. The patient may present acutely in the immediate post-injury timeframe, or the patient may not present for quite some time if the injury is more chronic. In both situations, pain and occasionally weakness may be present, especially when attempting to hold onto objects (pincer grasp mechanism in particular). 

The physical examination can be especially helpful in discerning this diagnosis. Perform a valgus stress test by abducting the thumb at its base can help to determine if any laxity or complete disruption of the ulnar collateral ligament exists. Contralateral comparison with the unaffected thumb can help to establish a baseline to delineate the degree of tear or injury further. In situations where partial tears exist, there is increased laxity or mobility on valgus stress testing. A lack of any endpoint during such testing would portend a complete tear with complete instability at the thumb base. One method to help isolate the ulnar collateral ligament during testing is first to ask the patient to flex the first metacarpophalangeal to 45 degrees. This helps to more specifically test the ulnar collateral ligament rather than other ligaments at the thumb base.

Based on orthopedic studies, the typical degree of laxity, which should raise suspicion for ulnar collateral ligament injury, is any amount greater than 15 to 20 degrees on abduction or valgus stress testing. This should be compared to the unaffected thumb. Furthermore, if the degree of laxity is more than 30 degrees, this is very suggestive of ulnar collateral ligament tear.  While this is described in the orthopedic literature, in the actual clinical environment, the provider may have difficulty accurately measuring the degree of ulnar collateral ligament laxity.[8]

Evaluation

Imaging in the setting of an acute ulnar collateral ligament injury is typically not helpful. However, plain films can be performed of the thumb to rule out fracture or bony abnormalities, in particular of the thumb base (proximal phalanx). The ulnar collateral ligament inserts along the medial (ulnar) aspect of the proximal phalanx of the thumb. Hence, an avulsion fracture may be present in the setting of ulnar collateral ligament injury.   In the vast majority of cases, however, plain x-ray imaging is normal or unrevealing in these patients.

In the hands of experienced ultrasound providers, this modality can be used at the bedside in real-time to assess laxity at the first metacarpophalangeal joint. Similar to the physical exam, ultrasound imaging can be done on both thumbs to compare one side to another and to establish a baseline on the unaffected side.

Magnetic resonance imaging is difficult to obtain acutely, but this technique has the highest sensitivity and specificity for the diagnosis of ulnar collateral ligament injury, including tears or ruptures.

Treatment / Management

As with most musculoskeletal injuries, ulnar collateral ligament injuries can be treated acutely with R-I-C-E therapy:  rest, ice, compression, and elevation. Immobilization is also helpful through the application of a thumb spica splint.[9]

If the patient has a bony injury such as avulsion fracture in the setting of ulnar collateral ligament injury, they should be referred urgently to an orthopedic or hand specialist. Similarly, if the physical examination shows significant laxity (greater than 15 to 20 degrees compared to the contralateral unaffected side or greater than 30 degrees absolute), then consultation or urgent referral to a hand surgeon is indicated.  

Splinting immobilization may suffice for treating partial tears, but hand surgery evaluation is still prudent. The typical immobilization timeframe recommended is three weeks. Subsequently, these injuries that are treated nonsurgically can then undergo physical therapy and rehabilitation. Therapy includes both passive and active measures, along with strengthening exercises. Immobilization is recommended when the patient is not actively undergoing physical therapy for a period of an additional three weeks, yielding a total of approximately six weeks of immobilization therapy. For those patients that have persistent weakness or pain after this timeframe, surgical referral should be pursued.

In most reported series, those patients who sustain complete ulnar collateral ligament tears who undergo surgery do well without significant complications. Generally, early surgical intervention is required for complete tears to prevent the development of the complication known as the Stener lesion. This complication occurs when the disrupted end of the ulnar collateral ligament migrates superficially and lies on top of the adductor pollicis aponeurosis and muscle. The ligament cannot heal appropriately given this altered anatomy, and surgery is recommended as the definitive treatment.[10]

Differential Diagnosis

The differential diagnosis for ulnar collateral ligament injuries includes other musculoskeletal injuries that may be sustained to the hand and thumb. This includes tendinous injury such as adductor pollicis disruption. This may also include any dislocation of the thumb at the metacarpophalangeal joint. Bony injuries such as Rolando or Bennett fractures should also be considered.  Arthritis of the thumb joint may also be considered.

Prognosis

Partial tears of the ulnar collateral ligament are usually treated with splinting alone and, despite the long duration of immobilization, tend to heal well. In a minority of patients, there may be persistent stiffness and pain. As discussed in the treatment and management above, surgery typically can be performed without significant complications in the setting of complete ulnar collateral ligament tears. In those individuals who develop Stener lesions or go without treatment, chronic changes can be observed to the metacarpophalangeal joint space.

Generally, the patient should wait at least six weeks before returning to work or sports.[11]