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© 1996 The Journal of Bone and Joint Surgery, Inc. Proximal Rupture of the Biceps Brachii with Slingshot Displacement into the Forearm. A Case Report*  , NEW YORK, N.Y.Investigation performed at the Departments of Orthopaedic Surgery and Radiology, The Hospital for Special Surgery, New York City
Disruption of the biceps brachii is unusual in persons who are less than fifty years old7,12,18,20-23,28. Rupture is generally secondary to either tendinopathy (distal) or tenosynovitis secondary to impingement (proximal), and it occurs almost exclusively in adults6,8,12,15,20. Proximal transection of the muscle belly has been described in military paratroopers10 and as a result of a direct blow14, although we are not aware of any reports identifying displacement of the distal portion of the musculotendinous unit. We present the case of a patient who had a traction injury to the proximal end of the biceps, which occurred with such force that the elastic recoil resulted in displacement of the musculotendinous unit around its intact distal insertion and into the forearm. To our knowledge, this is the first report of such an injury in any age-group.
A fifteen-year-old boy injured the right, dominant arm while waterskiing on a flotation device known as a boogie-board. The patient attempted to jump over the wake created by another skier while holding the towrope with the elbows flexed. The rope slackened as he reached the top of the jump and then suddenly went taut when the boat took up the tension in the line. The patient felt an acutely painful pop in the brachium and was unable to maintain his grip on the handle. He noticed weakness on attempted flexion of the elbow after he was helped into the boat. Family members noticed swelling in the anterolateral part of the forearm immediately after the injury. The patient was seen on the day of the injury by a local orthopaedist, who diagnosed a fracture of the elbow and recommended immobilization in a sling. During the ensuing twenty-four hours, swelling and ecchymosis developed over the brachium and the forearm, and the patient was referred to a regional academic center for additional evaluation. Standard radiographs were negative for fracture; radiographs of the contralateral limb were also made for comparison. Magnetic resonance imaging demonstrated a rupture of the proximal end of the biceps brachii with displacement of a large part of the biceps into the proximal part of the forearm. The long head of the biceps tendon appeared to remain in the bicipital groove. The patient was seen at our center three weeks after the injury after being referred for evaluation and management. At the time of the evaluation at our center, the patient had persistent dull, aching pain in the brachium and weakness on attempts to flex the elbow. He was unable to extend the elbow fully actively or passively. Clinical examination revealed a six by twelve-centimeter mass superficial and radial to the flexor-pronator mass and a corresponding cavitary defect in the brachium (Fig. 1). The patient had a 20-degree loss of active and passive terminal extension of the elbow. Testing revealed diminished motor strength with flexion of the elbow and supination of the forearm compared with the muscle strength of the contralateral limb5. Sensory examination revealed altered sensibility to light touch directly over the mass in the forearm. The results of sensory and motor examination elsewhere in the limb were within normal limits.
The findings on standard radiographs of the humerus, elbow, and forearm were unremarkable. Magnetic resonance imaging was repeated at our institution with use of additional scanning sequences. The proximal biceps tendon was intact and located in its groove proximally and was visible distally to the site of disruption at the musculotendinous junction. Parasagittal images demonstrated an intact insertion of the distal biceps tendon onto the biceps tuberosity of the radius. The insertion of the tendon was displaced distally, and the attached bulk of the biceps extended distally in the subcutaneous tissue to a point just proximal to the wrist joint. Axial images revealed the bulk of the muscle belly of the biceps to be located in the forearm superficial to the flexor-pronator mass in the subcutaneous tissue (Fig. 2).
With the patient under general anesthesia and with use of a sterile pneumatic tourniquet inflated to a pressure of 250 millimeters of mercury (33.33 kilopascals), the antecubital fossa and the forearm were explored through an extended anterior approach. The muscle belly of the biceps brachii was readily identified in the subcutaneous tissue (Fig. 3). The distal tendon was intact at its insertion onto the biceps tuberosity of the radius (Fig. 4). The branch of the musculocutaneous nerve innervating the muscle was not identifiable, and the muscle itself was devascularized. Additional exploration of the forearm revealed the proximal portion of the ruptured biceps to be located within five centimeters of the wrist flexion crease. It was elected not to attempt to reinsert the biceps because of the observed neurovascular disruption and the necrotic condition of the muscle. The intact distal insertion of the biceps was preserved and tagged for possible reconstruction in the future. Full passive extension of the elbow was noted after excision of the muscle.
The postoperative recovery was uneventful, and the patient was discharged on the second postoperative day. He diligently completed a rehabilitation program for restoration of motion of the elbow, shoulder, and wrist as well as strength-training. At the clinical evaluation one year after the injury, the patient had resumed normal activities and had no limitations related to the injury. He had a normal range of motion of the shoulder, elbow, and wrist. He continued to have less strength on flexion of the elbow of the injured limb compared with that of the contralateral limb, although no difference was detected when supination of the forearm and flexion, abduction, and rotation of the shoulder were tested. Both eccentric and concentric isokinetic testing also demonstrated the flexion deficit of the elbow (Table I). It is of interest that the patient had considerably greater strength on supination of the elbow and flexion of the shoulder on the side of the injury compared with that on the contralateral side (Table I). The patient was pleased with the result and did not desire additional operative intervention.
Pathological conditions involving the biceps brachii tendon include subluxation; dislocation; tenosynovitis; closed transection; distal rupture; and proximal rupture of the short or long head, or both1,4,9-11,14,19,27,28. Most reported ruptures have involved the proximal tendon of the long head2,9, with only a limited number involving the proximal tendon of the short head2,3,9,24 or the distal insertion of the biceps brachii1-3,8,9,23. Most ruptures (proximal or distal) occur in patients who are more than fifty years old7,12,17,21,22,24,28 and are thought to be the sequelae of long-standing pathological conditions6,15. While no form of disruption is common in patients who are less than twenty years old, closed intramuscular transection and proximal disruption were reported in twenty-eight military paratroopers who had been injured by the static line between the pack of the parachute and the interior of the aircraft10. It is possible that many of these individuals were in the second or third decade of life. Leffert and Rowe reported a closed transection of the muscle in a twenty-one-year-old mechanic secondary to a fall down an elevator shaft during which the brachium struck a steel bar. In another report, a nineteen-year-old man sustained a proximal rupture of the short head of the biceps while waterskiing7. The mechanism of injury was thought to be sudden resistance through the towrope against a flexed and adducted arm with the elbow extended. This mechanism is similar to that seen in our patient (except for the position of flexion of the elbow) and is illustrative of the high tensile loads that are an inherent hazard of waterskiing. Tremendous force is required to rupture the biceps tendon in an otherwise healthy patient. Cadaveric studies have suggested that the tensile strength of the tendon of the long head is 150 to 200 pounds (667 to 890 newtons)4,9. It is probable that the tensile strength of the biceps tendon is greater in an otherwise healthy adolescent and that the tissue in an adolescent has a relatively long elastic phase when exposed to tensile force. In our patient, the rupture occurred while the elbow was flexed, the shoulder was adducted, and the biceps was contracted to remove slack in the towrope. When the boat took up the slack, the biceps sustained an enormous eccentric load. This resulted in a disruption of the long and short heads proximally at the musculotendinous junction. While forced extension of the elbow against an eccentrically contracting muscle may explain the rupture of the long head of the biceps brachii, more information is necessary to explain why the injury also involved the short head. It has been shown that resistance to flexion and adduction of the elbow in the act of extension and abduction produces the greatest strain in the tendon of the short head7,24. This was precisely the mechanism of injury in our patient, and this could explain the pattern of injury. The elastic recoil at the time of the disruption catapulted the muscle belly over the intact insertion of the distal tendon and into the forearm. The muscle mass combined with the acceleration from the recoil produced a tremendous force that enabled subcutaneous dissection of the structure to its resting place distally. The functional role of the biceps brachii is thought to be primarily supination of the forearm and secondarily flexion of the elbow and the shoulder16,22,25-27. Deficits in strength on supination of the forearm as well as on flexion of the elbow and of the shoulder have been reported after traumatic disruption of the biceps4,13,16,20,22,25-27. Interestingly, one year after the injury, our patient had no loss of strength on supination of the forearm or glenohumeral flexion; in fact, he had equal or increased function of the injured limb compared with the uninjured limb on both concentric and eccentric isokinetic testing at all velocities (Table I). Some of this improvement in strength was probably related to the fact that the injury had been on the side of dominance. The patient's diligence in complying with a well supervised program of rehabilitation was probably also an important factor. A deficit in strength on flexion of the elbow was noted for both concentric and eccentric isokinetic testing at all velocities (Table I). This information demonstrates that, although the brachialis represents the primary flexor of the elbow, the biceps has a functional role as well.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
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