Disclosures: Peter C. Yeh, MD: Nothing to disclose

Case Description: Patient presented with a 5-month history of right biceps, forearm, and whole hand numbness and pain at the end of her pitch count. The pain worsened with overhead throwing during the wind-up phase at 120 degrees abduction in the 12 o’clock position. Previous right shoulder x-ray, MRI arthrogram, Cervical Spine MRI were negative. Intraarticular steroid injection and NSAIDS provided minimal relief. Examination was significant for pain on palpation along the right subacromial bursa and long head of the biceps, positive right supraspinatus isolation and resisted external rotation test, and reproduction of symptoms after 20 seconds of sustained forearm flexion with arm adduction.

Setting: Academic musculoskeletal clinic.

Patient: 16-year-old female softball pitcher.

Assessment/Results: Dynamic ultrasound revealed no evidence of tendinosis, tear, or tenosynovitis in the biceps brachii long head or rotator cuff but revealed subacromial and subdeltoid bursa effusions. Additional sonopalpation suggested musculocutaneous nerve (MCN) involvement. Electromyography revealed absent sensory response in the right lateral antebrachial cutaneous nerve distribution without evidence of right cervical radiculopathy or median, ulnar, or radial mononeuropathies. She initially underwent MCN hydrodissection with 2 months of symptom relief and a subsequent more proximal MCN hydrodissection between the coracobrachialis and short head of the biceps with near complete symptom resolution.

Discussion: The MCN arises from the brachial plexus and contains fibers from C5, C6, and C7 nerve roots. It innervates the biceps brachii, brachialis, and coracobrachialis and supplies lateral cutaneous sensation to the forearm. As it traverses through the coracobrachialis between the biceps brachii, it is at risk of compression, particularly with increase in strength training. Ultrasound is useful in examining nerve compression injuries and allows for targeted hydrodissection treatments. Hydrodissection has been used in carpal tunnel syndrome and other peripheral nerve entrapments, but less frequently in MCN entrapments.

Conclusion: By separating potential soft tissue adhesion or obstruction, hydrodissection can relieve nerve entrapment.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/hydrodissection-of-the-musculocutaneous-nerve-in-a-softball-pitcher-a-case-report/