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News For Orthopedic Surgeons, Plastic Surgeons, and Hand Surgeons

Every surgeon must know the details of the anatomy in the area being operated on. But sometimes the body throws a ringer that can surprise even the most experienced surgeons. That's the case in this report of a 70-year-old woman with carpal tunnel syndrome.

Carpal tunnel syndrome (CTS) is a common problem affecting the hand and wrist. Symptoms begin when the median nerve gets squeezed inside the carpal tunnel of the wrist, a medical condition known as nerve entrapment or compressive neuropathy. Any condition that decreases the size of the carpal tunnel or enlarges the tissues inside the tunnel can produce the symptoms of CTS.

This syndrome has received a lot of attention in recent years because of suggestions that it may be linked with occupations that require repeated use of the hands, such as typing on a computer keyboard or doing assembly work. Actually, many people develop this condition regardless of the type of work they do. And that is the situation with this patient.

When the surgeons made the surgical incision to treat the symptoms of carpal tunnel syndrome in the woman featured in this report, they found an extra muscle and tendon causing the problem. Any unusual or extra anatomical changes in the body are referred to as anomalous. In this case, it was a muscle called the palmaris profundus.

Studies show that only one out of 100 cases of carpal tunnel syndrome is ever caused by anomalous muscles. And only one out of 1600 people ever have the palmaris profundus muscle. So you can see this particular cause of carpal tunnel is very rare and worth reporting.

The woman's symptoms were clearly from compression of the median nerve with numbness and tingling of the affected hand and fingers during the day. At night she would wake up with pain and numbness in the fingers, hand, and forearm. When the symptoms started interfering with daytime activities, she went to the physician for help.

At first, they tried conservative (nonoperative) care, which is the standard treatment procedure. She took antiinflammatory medications and had steroid injections into the carpal tunnel to reduce any swelling that might be present. When those things didn't work, they did some additional testing. X-rays were normal but nerve conduction tests were abnormal.

When nerve conduction tests show an increased delay in signals along the nerve, the surgeon has a green light to perform a procedure to release the nerve from whatever is putting pressure on it. Many times the band of connective tissue that goes across the flexor tendons (called the flexor retinaculum) is cut and that takes care of the problem.

In this case, when the flexor retinaculum was cut, the surgeon could see the palmaris longus tendon (a muscle/tendon unit that is normally present in 90 per cent of all people). It was pressing on the nerve. When they moved up the palmaris longus tendon aside, they found the anomalous (extra) palmaris profundus.

They removed the palmaris profundus but before they cut into it, they checked to make sure it wasn't producing any movement or providing any function to the hand. By pulling gently on the palmaris profundus, they could see there was nothing happening (no movement of the fingers or hand).

The patient recovered completely with no residual symptoms. Four years later at the last follow-up, she was still symptom-free. The authors of this report provide a detailed description of the unusual anatomy for any other surgeons who may run into this problem.

They know from other studies that when present, the anatomy of the palmaris profundus varies from patient-to-patient. A report like this will help surgeons understand the potential for unusual anatomic anomalies as the cause of carpal tunnel syndrome.

A complete understanding of the normal anatomy is essential for recognizing when something is amiss. Knowing the course of the median nerve will also prevent any accidental cuts or damage to the nerve during carpal tunnel surgery.

Reference: Ahmed Elbardouni and Moradh Elyaacoubi. Carpal Tunnel Syndrome Caused by a Palmaris Profundus Muscle. In Journal of Orthopaedics. Vol. 8. No. 3. e4.

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