In this article, physicians from the University of Medicine and Dentistry of New Jersey (UMDNJ) bring us up to date on perilunate discloations. A perilunate dislocation is a wrist injury that occurs when there is enough force through the wrist to tear the ligaments and displace the lunate. The lunate is one of several wrist bones.
The injury really involves a series of damaging steps. First, the supporting ligaments are torn. As the load increases, a bone fracture can occur. The scaphoid bone next to the lunate takes the brunt of the force and fractures. With enough force, the lunate is then forced into the carpal canal.
The most common mechanism of injury is a fall onto the extended or outstretched hand. The palm is flat, the wrist is bent, and the full impact is on the wrist. When there’s enough force to cause bone fracture and dislocation, there can also be injury to the nerves and blood vessels in the area.
The diagnosis is missed in one-fourth of all cases. Early recognition of the problem is needed to avoid long-term problems and complications. There are two important diagnostic clues. The first is the rapid development of carpal tunnel syndrome (CTS).
With the lunate bone in the carpal canal, pressure is placed on the median nerve causing CTS. An obvious deformity (change in the wrist and hand appearance) may be present. There may also be a loss of blood flow to the median nerve below the level of the injury. If this happens, the hand and fingers may become cold and pale or blue/purple in color.
Symptoms of CTS include pain, numbness, and tingling of the wrist, thumb, index finger, and half of the middle finger (the side closest to the index finger). This is the part of the wrist and hand that the median nerve supplies with sensation.
The second diagnostic clue comes from X-rays taken of the wrist. To avoid missing the correct diagnosis, X-rays should be taken for all hand injuries. This recommendation comes from the American Society for Surgery of the Hand.
The authors also point out the importance of taking more than one radiographic view. A posteroanterior (back-to-front) view will not show a lunate dislocation. It is necessary to take a lateral (from the side) view. The lateral radiograph will clearly show the extent of the injury.
The physician will check the pulses to look for any vascular (blood vessel) damage. With a bone fracture and/or dislocation, there is usually loss of normal motion. Pain and swelling limit motion. With ligament damage, dislocation, and/or fracture, the wrist is unstable. Surgery is needed to repair and reconstruct the wrist.
The surgeon tries to restore full motion and function of the wrist and hand. A thorough examination and diagnosis is needed to know the full extent and possible effect of all the injuries. It will be necessary to realign the two rows of wrist bones with the radius and ulna (forearm bones) on one side of the wrist and the fingers on the other side.
Treatment depends on the amount and type of damage present. A simple dislocation without fracture and no signs of CTS can be reduced (bones put back in place). The procedure is done without an open incision. This procedure is called a closed reduction. The wrist and hand are immobilized in a splint or cast.
After the swelling goes down, the surgeon will re-evaluate the wrist to determine the need for operative treatment of the torn ligaments. Suture anchors are used to reattach the ligaments to the bone. Any fractures are treated at the same time. Pins or screws may be needed to fix or hold the bone in place. A long-arm cast from above the elbow down to the thumb and hand may be needed.
Anyone with rapid onset of carpal tunnel syndrome will need decompression of the median nerve. This requires the dislocation to be reduced and held in place with a wire until healing takes place. Sutures are used to repair the torn volar ligament across the carpal tunnel.
The prognosis is good for perilunate dislocation with early detection. Reduction and/or surgical treatment of the dislocation and any other bone or soft tissue injuries improve outcomes and limits disability. Recovery of full strength and motion can take six months to a year. Missed injuries with a delayed diagnosis do not respond as well.