]> 2026-07-31T07:52:04+00:00 WBR0558 0 en Axillary Nerve Musculocutaneous Nerve Posterior cord Union of C5-C6 nerve roots The supraspinatus is responsible for initiating shoulder abduction and is innervated by the suprascapular nerve, which originates from the superior trunk of the brachial plexus (C5-C6). All rotator cuff muscles are innervated by C5-C6. Union of C7-C8 nerve roots The union of the C7-C8 nerve roots represents the inferior trunk of the brachial plexus. Anatomy A 54-year-old man presents to the orthopedic surgeon with weakness and pain in his left shoulder. The pain began suddenly when the patient attempted to lift a heavy box one month ago. While the pain has largely subsided, the patient is still unable to initiate shoulder abduction. Physical examination of the left shoulder reveals decreased muscle bulk on the superior aspect of the scapula when compared to the right shoulder. MRI of the shoulder reveals a torn tendon. Which of the following areas of the brachial plexus gives rise to the nerve that normally innervates the injured muscle in this patient? D Musculoskeletal/Rheumatology 2020-10-28T00:57:27Z 2459150.5398958 WBR0558