Nerve Decompression

Nerve decompression surgically relieves pressure on a peripheral nerve that has become compressed by surrounding tissue.

A peripheral nerve can be compressed at any point where it passes through a confined space. Sustained pressure first interferes with blood flow, producing intermittent symptoms, then damages the myelin sheath, and finally the nerve fibres themselves, at which point recovery becomes incomplete. Decompression releases the specific structure causing the compression so the nerve can glide and its blood supply is restored. The operation is named for the site — carpal tunnel, cubital tunnel, radial tunnel, Guyon's canal — but the principle is identical, and its value lies as much in halting progression as in relieving symptoms.

Patients with a compression neuropathy confirmed clinically, and where useful on nerve conduction studies, whose symptoms have not settled with splinting, activity modification or injection. Surgery is indicated earlier, without exhausting non-operative measures, where numbness has become constant rather than intermittent, where two-point discrimination is reduced, or where there is muscle wasting or weakness in the nerve's distribution — each indicates axonal loss that will not recover if compression continues. Where symptoms are mild and intermittent and there is no objective deficit, continued non-operative treatment is reasonable. Compression at more than one level along the same nerve is recognised and changes the plan.

Most decompressions are day cases under local or regional anaesthesia, taking fifteen to forty minutes depending on site. An incision is made over the point of compression, the nerve is identified and protected, and the compressing structure — a ligament, fascial band, thickened retinaculum or fibrous arcade — is divided completely along its length. Incomplete division is the commonest technical cause of failure, so the release is carried beyond the constriction in both directions and the nerve is inspected along its course for a second point of compression. Where the nerve is unstable after release, as can happen at the elbow, it may be repositioned. The wound is closed and a light dressing applied that permits immediate movement.

Movement starts immediately and nerve gliding exercises begin within days. Sutures are removed at ten to fourteen days. Night symptoms and intermittent tingling frequently improve within the first week, which is often the earliest sign the release has worked. Constant numbness improves far more slowly, over months, as the nerve regenerates at roughly a millimetre a day from the point of release. Muscle strength, where it has been lost, recovers last and may take a year. Light activity resumes within days, driving at one to two weeks, and heavy work at four to six weeks. Scar tenderness settles over two to three months.

Scar tenderness and temporary weakness are usual. Infection is uncommon. Incomplete relief is the most frequent disappointment and arises from incomplete release, a second site of compression, or a nerve already too damaged to recover. Injury to the nerve or its branches is rare but is the most serious risk, and small sensory branches crossing the incision can leave a numb patch or a tender neuroma. Recurrent compression from scar tissue occurs and is harder to treat than the original problem. Complex regional pain syndrome is rare. The point to be clear about before surgery is that decompression stops ongoing damage reliably, but where nerve fibres have already been lost, some numbness or weakness may be permanent.