Working Diagnosis:
Complete rupture coracobrachialis tendon with retraction

Treatment:
The patient was started on conservative treatment based on a number of factors and followed up 3-4 weeks after the initial injury. At the time with all imaging, it was decided to continue with conservative management due to a number of factors, namely: he had regained full strength, he had no range of motion deficits, and this was his non-dominant arm. Additionally, there was only 11 mm of tendon retraction which effectively preserves the muscle length tension relationship and enables the muscle to function very close to its normal abilities once fully healed. Finally the short head of the biceps tendon was still intact and shared a common origin with the coracobrachialis which will serve as a scaffold for the healing coracobrachialis tendon.

Outcome:
After 6 weeks out from the injury the patient began to slowly return to play as tolerated including baseball without any recurrence of pain or reported weakness.

Author's Comments:
Coracobrachialis ruptures are extremely rare and typically are the result of direct blunt trauma or a penetrating injury. Typically the short head of the biceps tendon as well as the subscapularis can be involved. More commonly the rupture tends to occur at the distal aspect of the humeral insertion. Additional considerations would be for any possible traction neuropathy of the musculocutaneous nerve as it passes through the coracobrachialis muscle belly which could present as lateral forearm paresthesias and weakness with elbow flexion.

Editor's Comments:
The coracobrachialis muscle, when injured, has been largely involved with traumatic injuries to the distal aspect of the muscle as mentioned by the author. Rarer are proximal injuries, and rarer still are injuries to the coracobrachialis in isolation while leaving the remainder of the conjoint tendon intact which arises from the apex of the coracoid and includes the short head of the biceps tendon.

Of additional note is the considerable anatomic variation in the coracobrachialis muscle. The most common morphology (49.5%) is an origin at the apex of the coracoid of a single head and insertion at the medial middle portion of the shaft of the humerus. The most common variation (42.5%) presents as an accessory head of the muscle originating from either the tendon of the short head of the biceps or directly from the apex of the coracoid process. Additional, less common variations (7.9%) exist including those in which there are more than two heads to the muscle and specific tunnels for the median and musculocutaneous nerves thus putting each at greater risk for a traction neuropathy.

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