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Atraumatic snapping brachialis in a 37-year-old woman

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Atraumatic snapping brachialis in a 37-year-old woman

Bruce S. Rudy, MS, PA-C; April D. Armstrong, MD

The authors work in the Department of Orthopaedics and Rehabilitation, Penn State Milton S. Hershey Medical Center, Hershey, Pa. They have indicated no relationships to disclose relating to the content of this article. Steve Wilson works in cardiac, thoracic, and vascular surgery at the Heart Center, Peninsula Regional Medical Center, Salisbury, Md, and is a member of the JAAPA editorial advisory board.

Brachialis muscle (brachialis anticus) injury is an uncommon cause of pain or incapacitation in the adult population. Accurate diagnosis can be difficult even with today’s technological advances. Surgical exploration may be necessary to make a definitive diagnosis.

Case study

A 37-year-old woman, right-hand dominant, presented with a 9-month history of a nontraumatic popping sensation over the anteromedial aspect of the left elbow. She denied any associated symptoms such as numbness, tingling, burning, or paresthesias.

The physical examination revealed no signs of edema, erythema, or ecchymosis upon gross inspection. Active range of motion (ROM) of the elbow was complete, as was passive ROM in flexion, extension, pronation, and supination. Ulnar Tinel’s sign of the elbow was negative, and the ulnar nerve did not subluxate from its groove. When the elbow was extended approximately 20 degrees, there was a palpable snapping sensation in the anteromedial aspect of the elbow. This snapping was painful, and the patient avoided positions of the elbow that would cause her to extend it beyond 20 degrees.

Initial imaging studies—including radiography (see Figures 1 and 2), MRI (see Figures 3 and 4), and CT (see Figures 5 and 6)—were unremarkable. Because the diagnostic tests were largely negative, a snapping tendon was deemed the cause of the symptoms. Dynamic ultrasonography (US) was then ordered, and it demonstrated the brachialis muscle versus the pronator teres muscle translating over the medial trochlea of the distal humerus (see Figure 7). Additional US findings included possible protuberance of the medial ridge of the trochlea.

The patient was offered surgical exploration of the elbow for release of the brachialis versus pronator teres as well as possible excision of the bony protuberance. During surgery, the brachialis muscle was identified and appeared to be snapping over the natural bone of the trochlea at its most medial edge. As the elbow was extended past 20 degrees, the most medial portion of the brachialis snapped medially over the medial prominence of the trochlea. With flexion of the elbow, the brachialis snapped back over the trochlea laterally. Assurance of the trochlea was confirmed by placing a spinal needle into the natural bone using fluoroscopy visualization. Attention was then directed toward transversely releasing the muscle and fascia snapping over the trochlea. The median nerve was identified and protected during the dissection. Prior to closure, the patient had full ROM without any residual snapping during full extension of the elbow.

The patient began a progressive ROM and strengthening program. At follow-up examinations, she reported no further pain or snapping sensations of the elbow.

Discussion

The brachialis muscle is an uncommon, rarely discussed cause of elbow pain. A flattened fusiform muscle that lies posterior to the biceps muscle, the brachialis originates on the distal half of the anterior surface of the humerus and inserts on the coronoid process as well as the tuberosity of the ulna1 (see Figure 8). Common causes of elbow pain include lateral and medial epicondylitis, medial and ulnar collateral ligament tears, and osseous injuries,^2,3 but injury of the brachialis muscle is uncommon. Unusual reports include isolated necrosis due to exercise,⁴ isolated rupture of the muscle,⁵ and tuberculous abscess of both the brachialis and biceps muscles.⁶ In one case, a snapping brachialis tendon with associated median neuropathy followed a hyperextension injury.⁷ Our patient reported no trauma with associated pain and paresthesias.

Other reported causes of snapping of the elbow include instability, loose bodies, hypertrophic synovial folds interposed at the radiocapitellar joint or radiohumeral joint,^8-10 annular ligament,⁹ and snapping of the medial head of the triceps tendon over the medial epicondyle.^11-13 There has been one report of snapping of the elbow associated with a portion of the triceps tendon’s gliding over the lateral epicondyle.¹⁴ Pain and snapping in these cases is typically described in the lateral or posterior location of the elbow. These pathologies were excluded from the differential diagnosis in our patient, who had isolated anteromedial pain and snapping.

Another source for reported pain at the anteromedial location of the elbow is entrapment of the median nerve at the pronator teres, which has also been referred to as the pronator teres syndrome.^15-17 The pronator teres, a fusiform muscle that originates on the medial epicondyle of the humerus and coronoid process of the ulna, inserts in the middle of the lateral surface of the radius.¹ The main action of this muscle is assisting the pronator quadratus in pronation of the forearm. Although it has been associated with entrapment of the median nerve, usually between the two proximal heads of the muscle,¹⁸ the pronator teres is more commonly associated with climbing injuries³ and medial epicondylitis.²

Differentiation of the brachialis and pronator teres muscles was difficult during US in our patient. Pain upon resisted elbow flexion with the wrist pronated correlates to the pronator teres, while pain on flexion with the forearm supinated corresponds to biceps pathology.³ Our patient had no pain upon resisted forearm rotation. Pronator teres syndrome is not usually associated with snapping sensations; it is primarily associated with neuropathic pain located in the proximal volar forearm and paresthesias in the median nerve distribution.

Conclusion

We report a snapping brachialis as the source of a patient’s anteromedial elbow pain and palpable snapping. Only one previous case of a snapping brachialis has been reported in the literature, and this was associated with a previous traumatic event.⁷ In our patient, the signs and symptoms developed insidiously over 9 months, and dynamic diagnostic US provided the most assistance with diagnosis. Elbow pain is a common complaint in orthopedic practice. The brachialis muscle should be considered when a patient complains of painful anteromedial snapping of the elbow.

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