The rotator cuff is a group of muscles and tendons extremely important for the function of the shoulder. Tearing of the rotator cuff tendons represents one of the most common reasons of shoulder pain, weakness and poor function (Acute Tears of the Rotator Cuff: Why seek Help Immediately?; A Few Common Questions About Rotator Cuff Tears: How Do They Happen? Do They Heal? Do They Get Bigger? Why?; Arthroscopic Repair of the Rotator Cuff: How is it Done? What to Expect?). Less commonly, certain rotator cuff muscles may not function well due to a nerve problem.
Nerves are bundles of fibers that transmit electric impulses to and from the brain and spinal cord; these electric impulses initiate muscle contraction, and also provide background information to the brain through sensation or pain. Two of the rotator cuff muscles (the supraspinatus and infraspinatus) are controlled by the so-called suprascapular nerve. This nerve is at risk for excessive abnormal pressure that may lead to pain as well as weakness and atrophy of one or two of these muscles. The suprascapular nerve is relatively small, but when compressed it may be responsible for lots of trouble around the shoulder!
Where is the suprascapular nerve?
The suprascapular nerve is formed by nerve fibers from the 5th and 6th cervical roots. In order to reach its two muscle targets, this nerve first passes through a small notch on the top of the shoulder blade (suprascapular notch, “supra” = top, “scapula” = shoulder blade). A bundle of dense collagen fibers, the suprascapular ligament, closes the top of the notch, with the nerve passing underneath. Occasionally, the suprascapular ligament is partially or completely replaced with bone. The suprascapular nerve provides branches to the supraspinatus muscle, and then continues around the perimeter of the glenoid, which is the portion of the shoulder blade that contains the socket of the shoulder joint. It passes underneath the larger spine of the scapula, through the so-called spinoglenoid notch, to reach the infraspinatus muscle.
What can cause issues with the suprascapular nerve?
The term “neuropathy” is used in Medicine to indicate poor nerve function. Suprascapular neuropathy is almost always secondary to the nerve being squeezed under a cyst, or the nerve being pulled excessively while tethered.
Squeezing of the nerve is commonly the consequence of a so-called paralabral ganglion cyst. Tears of the shoulder labrum are discussed in detail in our blog (My Shoulder Superior Labrum is Torn: Do I Need Surgery?). The labrum seals the shoulder joint. Labral tears may allow joint fluid to leak outside and collect into a cyst that eventually compresses the suprascapular nerve.
Excessive traction of the nerve may occur in patients with a partially ossified or a very tight suprascapular ligament, especially after an injury or after playing certain sports, such as volleyball, tennis or baseball. Some believe that very large rotator cuff tears may lead to nerve stretching as the muscles retract.
When to suspect a suprascapular neuropathy?
Shoulder pain, weakness and atrophy represent the hallmarks of suprascapular neuropathy. When the nerve is affected around the suprascapular notch, both the supraspinatus and the infraspinatus muscles are affected, whereas compression or traction injuries at the spinoglenoid notch will affect only the infraspinatus muscle.
The typical patient with suprascapular neuropathy is relatively young. Pain may be severe, mild or minimal. Looking at these patients from the back, the bulk of the muscle on the lower part of the scapula is noticeably smaller compared to the other shoulder. Weakness is particularly severe when trying to push out with the arm (external rotation). Suprascapular nerve pain can sometimes be elicited by moving the shoulder backwards while the head is tilted to the opposite shoulder.
Your shoulder specialist will likely ask you about throwing activities or an injury. It will also be important to find out if there is a labral tear with a cyst, which typically requires confirmation with magnetic resonance or ultrasound. The main test used in Medicine to assess nerves in general is called electromyogram with nerve conduction studies (abbreviated EMG). As other tests in Medicine, EMG is abnormal in many, but not all, patients with suprascapular neuropathy.
What are the treatment options?
Sometimes, a suprascapular neuropathy will resolve just by stopping the inciting activity (tennis, volleyball or other) and giving the nerve some time to recover. In the mean time, physical therapy should be initiated in order to restore strength. Occasionally, cortisone can be injected around the nerve under ultrasound guidance to speed up the recovery.
When a cyst is confirmed to be the reason for nerve compression, surgery is recommended. The labrum is repaired with arthroscopic surgery to seal the joint, so that the cyst does not collect fluid any more. Large cysts may be emptied or removed as well.
In the absence of a cyst, compression of the suprascapular nerve that will not recover spontaneously can be treated by dividing the suprascapular ligament and removing any adjacent excessive bone. It is important not to wait a long, long time before decompressing the nerve, since once severe muscle atrophy is established, normal muscle strength is very difficult to recover.