The flexor retinaculum is a strong, fibrous band that attaches to the pisiform and the hamulus of the hamate. The proximal boundary is the distal wrist skin crease, and the distal boundary is approximated by a line known as Kaplans cardinal line. This line uses surface landmarks, and is drawn between the apex of the skin fold between the thumb and index finger to the palpated hamate hook. Pathophysiology
The median nerve can be compressed by a decrease in the size of the canal, an increase in the size of the contents (such as the swelling of tissue around the flexor tendons), or both. When the pressure builds up inside the tunnel, it damages the median nerve (median neuropathy). As the median neuropathy gets worse, there is loss of sensibility in the thumb, index, middle, and thumb side of the ring finger. As the neuropathy progresses, there may be first weakness, then to atrophy of the muscles of thenar eminence (the flexor pollicis brevis, opponens pollicis, and abductor pollicis brevis). The sensibility of the palm remains normal because the superficial sensory branch of the median nerve branches proximal to the TCL and travels superficial to it.The role of nerve adherence is speculative. Epidemiology
IMNCT is estimated to affect one out of ten people during their lifetime and is the most common nerve compression syndrome.
Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunnel (IMNCT). Idiopathic means that there is no other disease process contributing to pressure on the nerve. As with most structural issues, it occurs in both hands, and the strongest risk factor is genetics.Other conditions can cause CTS such as wrist fracture or rheumatoid arthritis. After fracture, swelling, bleeding, and deformity compress the median nerve. With rheumatoid arthritis, the enlarged synovial lining of the tendons causes compression. The main symptoms are numbness and tingling in the thumb, index finger, middle finger and the thumb side of the ring finger. People often report pain, but pain without tingling is not characteristic of IMNCT. Rather, the numbness can be so intense that it is described as painful. Symptoms are typically most troublesome at night. Untreated, and over years to decades, IMNCT causes loss of sensibility and weakness and shrinkage (atrophy) of the muscles at the base of the thumb. Work-related factors such as vibration, wrist extension or flexion, hand force, and repetition increase the risk of developing CTS. The only certain risk factor for IMNCT is genetics. All other risk factors are open to debate. It is important to consider IMNCT separately from CTS in diseases such as rheumatoid arthritis.Diagnosis of IMNCT can be made with a high probability based on characteristic symptoms and signs.