Gamekeeper's thumb: ulnar collateral ligament injury

Author: J. Randall Richard
Date: April, 1996

Chronic laxity of the ulnar collateral ligament, or gamekeeper's thumb, was first described in 1955[1] among British gamekeepers. This occupational injury and the resultant disability were related to the way in which rabbits and other small game caught in snares were killed. The animal's neck was held tightly between thumb and forefinger and was forcefully hyperextended. This repetitive action led to a chronic laxity of the ulnar collateral ligament, with subsequent instability of the first metacarpophalangeal joint. Functional disability and arthritis often resulted. Today, this injury is often acute and occurs more commonly in skiing accidents, when the thumb is abducted against the ski pole or the ground.[2]

In the setting of the acutely injured ulnar collateral ligament, it is important to differentiate between partial and complete tears of the ligament, since surgical exploration and repair are indicated for complete tears. Partial tears, diagnosed by careful clinical and radiographic examination, are sufficiently treated with simple short-arm thumb spica casting. Knowledge of the key clinical diagnostic features of acute injury of the ulnar collateral ligament helps the family physician differentiate partial from complete ligament tears.

Illustrative Case

A 17-year-old boy who played as a defensive lineman on the high school football team complained of pain and swelling of the first metacarpophalangeal joint, which was worsened by pinching the thumb against the forefinger. During a practice session, the patient's left thumb had been forcibly abducted and hyperextended as he endeavored to hold back a rushing opponent.

Mild to moderate swelling and point tenderness of the ulnar aspect of the joint were evident on physical examination. A radiograph revealed a nondisplaced chip fracture of the ulnar aspect of the proximal end of the proximal phalanx, which corresponded with the point of maximum tenderness (Figure 1). Stress testing of the metacarpophalangeal joint was not performed. The patient was placed in a short-arm thumb spica cast for six weeks.

At follow-up, the patient had no pain on palpation of the ulnar aspect of the metacarpophalangeal joint, nor was there any laxity or pain with lateral (radial) stress of the metacarpophalangeal joint in full flexion. The patient had no pain or weakness associated with pincer grasp. Follow-up radiographs showed union of the chip fracture. After appropriate reconditioning, including heat application and range-of-motion exercises, the patient returned to sporting activities.

ANATOMY AND FUNCTION

The metacarpophalangeal joint of the thumb is stabilized by a combination of ligaments and musculotendinous attachments. One of the insertions of the adductor pollicis muscle is on the lateral tubercle of the proximal phalanx; dorsally, this muscle expands to form the adductor aponeurosis, which attaches to the proximal phalanx (Figure 2). Also, the adductor aponeurosis envelops the extensor pollicis longus tendon dorsally and, thus, slides distally with flexion of the metacarpophalangeal joint and proximally with extension. In this configuration, the adductor aponeurosis acts as an important dynamic stabilizer against thumb abduction.[3]

The ulnar collateral ligament originates on the metacarpal head and inserts on the ulnar aspect of the proximal phalanx. It provides static stabilization of the thumb metacarpophalangeal joint. It is typically 4 to 8 mm wide and 12 to 14 mm long. The ulnar collateral ligament consists of a proper portion and an accessory portion (Figure 3). In maximum flexion of the metacarpophalangeal joint, the ulnar collateral ligament proper is taut while the accessory portion of the ligament is lax; in maximum extension of the metacarpophalangeal joint, the opposite is true. Therefore, it is in flexion of the metacarpophalangeal joint that the main body, or ulnar collateral ligament proper, provides maximum lateral stabilization of the metacarpophalangeal joint. This important feature relates to the clinical examination for lateral instability (i.e., stress testing), discussed in a subsequent section. The ulnar collateral ligament also prevents volar subluxation of the metacarpophalangeal joint. From person to person, there is a high degree of variability in the motion of the metacarpophalangeal joint, which depends primarily on the particular shape of the metacarpal head. Persons with less range of motion are generally more susceptible to injury.

MECHANISM OF INJURY

While chronic laxity of the ulnar collateral ligament results from repetitive lateral stress applied to the metacarpophalangeal joint, the acute injury that commonly occurs in skiers results from a sudden forced abduction stress at the metacarpophalangeal joint, such as in a fall against a ski pole or the ground. Interestingly, the incidence of injury to the acute ulnar collateral ligament of the thumb has not diminished with newer ski pole designs that feature modified strapless grips.[4] The mechanism of injury probably also involves forced hyperextension of the metacarpophalangeal joint. The distal attachment on the proximal phalanx is the most frequent site of rupture.[5]

In 1962, Stener[6] reported a high incidence of entrapment of the ruptured end of the ulnar collateral ligament outside the adductor aponeurosis. This finding was present in 25 (64 percent) of 39 cases, all of which were surgically treated because of instability of the metacarpophalangeal joint.

Although the incidence of entrapment of the ruptured end of the ulnar collateral ligament proper outside the adductor aponeurosis has been reported to be between 14 percent and 87 percent,[3] most authors have noted the presence of the Stener lesion (diagnosed definitively at surgery) in at least 50 percent of cases of complete rupture. This finding is significant because the ruptured end of the ligament becomes abnormally placed outside the adductor aponeurosis, thereby preventing anatomic healing (Figure 4). Thus, early surgical repair is the general recommendation in cases of suspected complete tear of the ulnar collateral ligament.

CLINICAL EVALUATION

The patient with metacarpophalangeal joint injury presents with a painful, swollen metacarpophalangeal joint. Additionally, pain and, sometimes, weakness are associated with pincer grasp. Maximal tenderness is present over the ulnar aspect of the metacarpophalangeal joint. If there is a history of a hyperabduction injury, radiographs should be obtained to identify fracture before lateral stress testing is carried out. Most authors agree that stress testing may cause displacement of an avulsion fracture of the proximal phalanx that was originally displaced less than 5 mm (Figure 1), thus necessitating open surgical treatment.[7]

If radiographs do not show a fracture, complete ulnar collateral ligament rupture is stiff possible. Stress examination is performed by stabilizing the thumb metacarpal with one hand to prevent rotation, and then, with the metacarpophalangeal joint in maximum flexion, applying lateral (radial) stress on the joint (Figure 5). The ulnar collateral ligament proper (rather than the ulnar collateral ligament accessory) is lax with the metacarpophalangeal joint in extension, but it is taut with the joint in flexion, which is the position of maximal stability. Therefore, with a complete tear of the ulnar collateral ligament proper, the joint will open up significantly and without a definite "end point" during stress examination with the metacarpophalangeal joint in flexion.

Controversy exists over the degree of angulation, detected during stress examination, that constitutes a complete ulnar collateral ligament tear. However, based on cadaveric and clinical studies, most authors agree that angulation of 35 degrees or more, or angulation of more than 15 degrees when compared with the uninjured side, constitutes complete rupture and requires surgical repair.[8] Some authors also consider the presence of any volar subluxation of the proximal phalanx on the metacarpal head to be an indication for surgery.[5]

Stress examination may be quite painful and, in order to complete a thorough examination, local anesthesia may be necessary. Although the anesthetic can be administered directly at the metacarpophalangeal joint, the thumb is best anesthetized by means of combined medial nerve and radial nerve blocks.[9]

The Stener lesion, discussed in the preceding section, cannot be accurately diagnosed on the basis of clinical findings. Because it occurs in at least 50 percent of cases of complete ulnar collateral ligament rupture, and because its presence prevents anatomic healing, all patients with suspected complete ulnar collateral ligament rupture should be referred for possible surgery.

RADIOGRAPHIC EVALUATION

Plain radiographs, to rule out fractures at the proximal phalanx, should be obtained before stress testing. Avulsion fractures displaced with a gap greater than 5 mm or any fracture involving 25 percent or more of the metacarpophalangeal joint surface requires surgical treatment.[5] The role of stress radiography is controversial; little agreement exists regarding how the films should be obtained or interpreted to confirm or rule out complete ulnar collateral ligament rupture. Additionally, radiographs are difficult to obtain with the metacarpophalangeal joint in flexion.[8] Arthrography has not proved consistently helpful in confirming complete ulnar collateral ligament rupture or in identifying the presence of the Stener lesion. Magnetic resonance imaging (MRI) can be helpful but is expensive. Ultrasound may be a useful and economic diagnostic modality, with fairly good sensitivity for complete rupture and with results comparable to those of MRI[10] but, at present, it is not widely used.

At best, the role of radiographic testing is supportive but not confirmatory, except in cases of displaced or large proximal phalanx fractures. If a complete ulnar collateral ligament rupture cannot be ruled out based on the clinical parameters discussed earlier, then orthopedic consultation is indicated.

TREATMENT

Partial tears of the ulnar collateral ligament (i.e., those with less than 30 to 35 degrees of angulation on lateral stress testing) and ulnar collateral ligament injuries associated with small avulsion fractures and a gap of less than 5 mm generally have a good prognosis and can be treated with a well-molded, short-arm thumb spica cast[11] (Figure 6), with the metacarpophalangeal joint in slight flexion for four to six weeks.[3] A smaller, glove-type thumb spica cast, which allows wrist flexion and extension, has been used[12] (Figure 7). Casting is followed by a period of active metacarpophalangeal joint flexion exercises and a gradual return to activities.

Complete tears of the ulnar collateral ligament should be surgically explored to identify the Stener lesion and restore proper anatomic positioning of the ligament. If complete ulnar collateral ligament ruptures are left untreated, weakness and painful pincer grasp develop in most patients and development of painful arthritis is likely.[8] Results of surgical repair are superior if surgery is carried out within two to three weeks of the acute injury.[5] Therefore, early referral is indicated, especially if uncertainty exists about whether a complete ulnar collateral ligament tear is present. Surgical treatment is indicated for patients with avulsion fractures displaced greater than 5 mm, for patients with a large (greater than 25 percent) articular surface fracture of the proximal phalanx and for patients with volar subluxation of the proximal phalanx evident on stress examination.

REFERENCES

[1.] Sternbach G. C.S. Campbell: gamekeeper's thumb. J Emerg Med 1984;1:345-7. [2.] Rettig AC, Wright HH. Skier's thumb. Physician Sportsmed 1989;17:65-7,71-2,75. [3.] Kozin SH, Bishop AT. Gamekeeper's thumb. Early diagnosis and treatment. Orthop Rev 1994;23:797-804. [4.] Primiano GA. Skier's thumb injuries associated with flared ski pole handles. Am J Sports Med 1985; 13:425-7. [5.] Green DP, Rowland SA. Fractures and dislocations of the hand. In: Rockwood CA Jr, Green DP, Bucholz RW, eds. Fractures in adults. 3d ed. Philadelphia: Lippincott, 1991:531-6. [6.] Stener B. Displacement of the ruptured ulnar collateral ligament of the metacarpal phalangeal joint of the thumb: a clinical and anatomical study. J Bone Joint Surg [Br] 1962;44:869-79. [7.] Hankin FM, Wylie RJ. Gamekeeper's thumb. Am Fam Physician 1988;38(6):127-30. [8.] Newland CC. Gamekeeper's thumb. Orthop Clin North Am 1992;23:41-8. [9.] Ferrera PC, Chandler R. Anesthesia in the emergency setting: part I. Hand and foot injuries. Am Fam Physician 1994;50:569-73. [10.] Noszian IM, Dinkhauser LM, Orthner E, Straub GM, Csanady M. Ulnar collateral ligament: differentiation of displaced and nondisplaced tears with US. Radiology 1995;194:61-3. [11.] Richard JR. Office orthopedics: thumb spica casting for scaphoid fractures. Am Fam Physician 1995; 52:1113-20. [12.] Primiano GA. Functional cast immobilization of thumb metacarpophalangeal joint injuries. Am J Sports Med 1986;14:335-9.

The Author

J. RANDALL RICHARD, m.d. is associate director of the family practice residency program at Barberton (Ohio) Citizens Hospital and associate professor of clinical family medicine at Northeastern Ohio Universities College of Medicine, Rootstown. He earned a medical degree at the University of Cincinnati College of Medicine and completed a family practice residency at St. Elizabeth Medical Center, Dayton, Ohio.

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