Cubital tunnel syndrome
At the inner side of the elbow the ulnar nerve (N. ulnaris) travels through a canal called sulcus ulnaris or cubital tunnel behind the medial epicondyle (the "funny bone"). This tunnel is formed by a ligament that spans this bony canal, through which the ulnar nerve is running. Because of the wide range of motion of the elbow, the nerve must be able to slide free within the canal. In cubital tunnel syndrome, there is compression of the nerve in this canal. The ulnar nerve innervates the little finger, the ulnar aspect of the ring finger, and controls a large part of the hand musculature (intrinsic hand muscles).
The superficial course of the ulnar nerve makes it susceptible to outside injury. Possible causes of ulnar nerve compression are:
- Thickening of the ligament spanning the canal
- Connective tissue fibrosis
- Strong developed muscle covering the canal (epitrochlear muscle)
- Mechanical irritation due to wide range of motion
- Arthrotic bone spurs (osteophytes) because of elbow arthrosis
- Frequent resting of arms on the inner side (medial aspect) of the elbow
Paresthesia, tingling, and numbness in the little finger, the medial side of the ring finger, and the medial (ulnar) aspect of the hand. These dysesthesias initially manifest themselves only with specific movements or with direct external pressure on the nerve. However, with increasing exertion of pressure, the dysesthesias no longer subside. Longstanding compression additionally leads to decrease of hand strength/grip and ultimately to muscle wasting. At this stage, the fingers can no longer be forcefully spread.
Case history and clinical findings lead to the suspected diagnosis. To confirm it, the neurologist will perform an electrophysiological examination, which tests the ability of the nerve to conduct electrical impulses. If it is suspected that either degenerative joint changes, or a ganglion within the cubital tunnel are responsible for the compression, radiographic or ultrasound imaging can be performed.
If the symptoms and the electrophysiological changes are only mild, conservative treatment without surgery is appropriate. This means avoiding movements and positions of the elbow, which lead to discomfort. If needed, an elbow brace including padding over the nerve can be worn. Hand therapy provides for performance of nerve-sliding exercises.
If conservative therapy is ineffective or sensory disturbances, muscle wasting, and/or clearly diminished nerve conduction developed already, surgery is inevitable. This means cutting the ligament that spans the sulcus ulnaris (cubital tunnel). Depending on the circumstances, the nerve is left in the canal (simple decompression) or is transferred to the anterior side of the elbow.
Simple decompression is performed either through an elongated incision in the skin of the medial surface of the elbow, or under camera visualization (endoscopic) through a smaller incision immediately anterior to the cubital tunnel. The anterior transfer can only be performed by an open approach, with a longer skin incision. Here the nerve is positioned either within the subcutaneous fatty tissue, or under the muscles (submuscular) of the inner elbow.
Follow up treatment
If the operation only includes cutting of the ligament and leaving the nerve in place, a two-week period of bandaging and rest is adequate. If the nerve is transferred to an anterior position under the musculature, both elbow and wrist are immobilized for two weeks to allow the disconnected musculature to heal. Depending on the operation, normal function can be regained after two to six weeks. Hand therapy allows the performance of nerve sliding exercises.
The prognosis depends on the degree of nerve damage at the time of the operation. As long as there is no irreversible damage, sensory function and strength can be completely recovered. This can however take weeks or months, especially with regard to sensory function. After longstanding compression with irreversible nerve damage, the symptoms will not fully resolve.
Occasionally, even after initial successful simple decompression, recurrent pressure associated with nerve compression can occur. During reoperation, the nerve is carefully freed of scar tissue and adhesions and transposed to the anterior side of the elbow. Accordingly, recovery time after such interventions will be longer than after primary surgery.