The flexor retinaculum of the hand is a fibrous band that is quite durable and extends over the carpus. The carpus is a group of bones located in the wrist between the ulna, the radius and the metacarpus. The arch of the carpus refers to a groove in the front of the carpal bones. The flexor retinaculum of the hand passes over this groove, converting it into the carpel tunnel. The median nerve and the flexor tendons pass through the carpel tunnel. The flexor retinaculum of the hand attaches to the middle of the pisiform, which is a small wrist bone that is shaped like a pea. It also attaches to the hamate bone's hamulus, which is a curved process that is located on the underside of the hamate bone. In addition, it attaches laterally to the scaphoid and across the middle of the trapezium. If the flexor retinaculum compresses the median nerve, carpal tunnel syndrome may occur. Symptoms include tingling, numbness, and pain in the wrists, hands, and forearm. Carpel tunnel syndrome may be caused by anything that leads to inflammation in the wrist. In some cases, it may be linked to other conditions, such as arthritis, or repetitive actions, like typing. In severe cases, treatment requires surgery to divide the flexor retinaculum.