Supinator Syndrome (Posterior Interosseous Nerve Palsy)

Definition

The posterior interosseous nerve may be compressed where it passes through the supinator muscle in the proximal forearm. This nerve controls finger extension, and to a small degree, wrist extension. Patients have pain and tenderness in the proximal forearm during activity and may have some degree of finger extension weakness compared to the normal arm. Numbness should not be present.

Diagnosis

Diagnosis is made by history and physical examination. It is then confirmed with electrical studies done in the office. Symptoms are often worse with forced supination (i.e., turning the wrist up), or repetitive forearm use. Supinator syndrome may be confused with nerve compression in the neck, (specifically the C8 nerve root) or certain forms of neuritis or amyotrophy. Therefore it is important to be evaluated by a specialist in neurological disorders. An MRI of the neck to exclude a herniated disk, as well as of the forearm to exclude a mass or cyst, may be ordered by your physician.

Supinator Syndrome

Patient with a right-sided posterior
interosseous nerve palsy causing
finger drop.

Treatment Options

Avoiding repetitive strain is recommended. Steroids may help some patients, but it is difficult to inject them near this nerve. If weakness is present, then physical therapy and a wrist splint with dynamic finger extension support is used. Surgery to decompress the posterior interosseous nerve should be considered if symptoms do not improve after three months of conservative therapy. If finger extension weakness is profound and electrical tests confirm nerve damage near the supinator muscle, or if there is a cyst or mass on MRI, then surgery may be recommended sooner.

Surgery

Decompression takes less than one hour and is performed in day surgery under general anesthesia. Using an approximate two-inch incision in the proximal forearm, the superficial forearm muscles are gently retracted to expose the supinator muscle and posterior interosseous nerve. The supinator muscle is partially opened, thereby decompressing the nerve. Supination weakness should not occur after the procedure because a large portion of the supinator muscle remains functional and other muscles (i.e., biceps) also supinate the forearm. All stitches are placed under the skin and absorb by themselves. Although this surgery can be performed via an incision on the back of the forearm, a front-sided incision is more frequently recommended.

Complications

Although decompression of the posterior interosseous nerve is routine, symptom resolution may not be complete after surgery. The reason for this is that permanent nerve damage may have already been present before surgery. Other risks include infection, bleeding, worsened pain, and the very remote chance of finger paralysis.

Day of Surgery

General anesthesia is used with or without intubation. Therefore, you should not eat or drink after midnight the night before surgery. You can take your routine medications the morning of surgery with a sip of water. You arrive about an hour before the surgery to meet with the anesthesiologist as well as the surgeon once again. Although the surgery takes about one hour, you will be in the operating room somewhat longer than that for cleaning, positioning, and dressing the wound. After the procedure, you are observed in the recovery room for about one hour and then are allowed to leave with a friend or family member taking you home.

Discharge Instructions

An occlusive dressing is applied to your forearm, which should be kept in place for 3 days. In general, you should keep the arm elevated above your heart for three days, which reduces swelling. You are encouraged to use the operated arm for light, daily activity. You may shower with the occlusive dressing. After three days the occlusive dressing is removed, revealing small stickers on the wound, which remain until you visit the surgeon one week after surgery in the office. Once again, you may shower and pat the stickers dry when done. Pain is usually minimal after supinator release, but the occasional Tylenol or percocet may be required. If you experience severe or progressive pain or bleeding, you should call the surgeon. Some small amount of blood on the dressing is normal.

Recovery

The operated arm should only be used for occasional light work during the first two weeks after surgery. Minimizing activity helps the wound heal well. For patients who only do light work in an office setting, they can return to work a few days after surgery. Following an initial two-week period, physical therapy is prescribed by the surgeon or physiatrist, which is performed on a progressive basis for about six weeks. During this time, most people already have returned to work. Although you may visit the physical therapist three times per week in the beginning, once the exercises are learned they can often be performed at home. By eight weeks after surgery you should have no restrictions with use of the arm. You will see the surgeon a second time two to three months after the procedure.

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