The rotator cuff consists of muscles and tendons that wrap around the head of the upper arm bone, holding it in place within the shoulder joint. The muscles of the rotator cuff include teres minor, the infraspinatus, the supraspinatus and the subscapularis. These muscles act together to lift and turn the upper arm within the shoulder joint. Three nerves supply the muscles of the rotator cuff. Injuries to these nerves can cause shoulder weakness and partial loss of arm mobility.
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The roots of the axillary nerve arise from the spinal cord in the lower neck. Five spinal nerve roots join in the neck to form the nerve bundle known as the brachial plexus. The axillary nerve emerges as a branch of the brachial plexus near the shoulder. The teres minor muscle of the rotator cuff receives innervation for the axillary nerve, enabling voluntary control of the muscle. The deltoid muscle, which covers the outer shoulder, also receives innervation from the axillary nerve.
The axillary nerve may sustain damage during rotator cuff repair or other shoulder surgery, notes the medical reference website Wheeless' Textbook of Orthopaedics. Shoulder dislocations and traumatic shoulder injuries may also damage the axillary nerve. Injury to the axillary nerve typically leads to an inability to raise the arm to the side and to turn the arm outward.
The roots of the suprascapular nerve arise from the spinal cord at the same site in the neck as the axillary nerve roots. The suprascapular nerve emerges from the brachial plexus and provides innervation to the supraspinatus and infraspinatus muscles of the rotator cuff. Other branches of the suprascapular nerve provide sensation to the shoulder joint.
Damage may occur to the suprascapular nerve with shoulder overuse, trauma or surgery, report Dr. Craig Cummins of Northwestern University Medical School and colleagues in a March 2000 article published in the Journal of Joint and Bone Surgery. Inflammation or compression of the suprascapular nerve can mimic the symptoms of a rotator cuff injury, notes Cummins. Irritation of the suprascapular nerve often causes aching shoulder pain, weakness raising the arm to the side and possible weakness turning the arm outward.
Similar to the other nerves of the rotator cuff, the subscapular nerve arises from the brachial plexus. It supplies innervation to the subscapularis muscle of the rotator cuff and teres major, a muscle between the shoulder blade and upper arm bone. Trauma, surgery or overuse of the shoulder may injure the subscapular nerve. Injury to the nerve may cause weakness or paralysis of the subscapularis muscle and difficulty turning the arm inward, notes Wheeless' Textbook of Orthopaedics.