Hand muscles bulge underneath the skin of your hand. The most obvious one is on the palm side of the thumb at the thumb base. These are the thenar muscles. Some or all of them may be supplied by the median nerve, the nerve affected by carpal tunnel syndrome.
The median nerve contains both sensory and motor nerve fibers – they supply finger sensation and muscle function to the thumb. As more pressure is put on the nerve and carpal tunnel syndrome goes on for a long time, the sensory nerve fibers are compressed and damaged first, followed by the motor nerve fibers. That's why muscle atrophy is a bad sign – the sensory fibers have already been damaged for a long time when you see muscle wasting.
You can tell if someone has muscle atrophy at the base of the thumb if the normally smooth, bulging contour of the muscle is bent or has a large “hollowed out” place in the palm, where the thumb joins up with the wrist.
This permanent weakness and loss of function is what hand surgeons are trying to prevent when they recommend and perform carpal tunnel surgery or other treatments.
Once the muscles have atrophied, even surgery may not help the nerve recover. Despite this fact, carpal tunnel surgery relieves pain (especially night-time pain) for many people with chronic carpal tunnel syndrome who have muscle atrophy. A steroid injection may also help with pain from median nerve compression, though it's illegally the shot will make the nerve recover completely.
The damaged muscles have a very specific function – opposition . This means lifting the thumb out and away from the palm of the hand. This motion is essential to let you get your hand around large objects, like a 2 liter bottle or to hold onto a large stack of books.
Tendon transfer surgery is the only way of restoring this function after the muscles have been damaged. Many types of tendon transfers have been described to treat this type of muscle atrophy. They involve moving an expendable tendon from one part of the hand and attaching that tendon to the thumb to replace the missing function. Surgeons use a term called opponensplasty to describe this operation. It makes sense, right? It restores that function I mentioned earlier – opposition .
Do not let your carpal tunnel syndrome get this bad – get treatment from a competent health care provider that you trust. Numbness and tingling are the first signs of carpal tunnel syndrome – do not ignore them!