Perilunate dislocations and fracture-dislocations are complex injuries to the small bones of the wrist. These small bones, called the carpal bones, comprise eight separate bones, each about the size of a sugar cube, wedged between the end of the forearm and the long bones of the hand. These carpal bones are critical to allow the complex bending and rotational movements of the wrist joint. One of these bones is called the lunate.
Lunate dislocations (more properly called “perilunate” dislocations) usually occur as part of a major injury such as a fall from a height or an automobile collision. When a perilunate dislocation occurs, one or more of these small carpal bones shifts out of normal alignment in the wrist joint. Sometimes, the injury occurs in association with a fracture of one of the carpal bones—this is called a perilunate fracture-dislocation.
Signs of a Perilunate Injury
The common symptoms of a perilunate dislocation or fracture-dislocation include:
- Significant pain in the wrist and palm of hand
- Swelling of the hand
- Limited motion of the wrist and hand
- Tingling and numbness of the fingers
The reason tingling and numbness are common in patients with a perilunate injury is that the lunate is just adjacent to the carpal tunnel in the wrist. The carpal tunnel is the space that contains the median nerve, one of the major nerves providing sensation to the hand and fingers. This is the nerve that is pinched in carpal tunnel syndrome. A perilunate dislocation can be the cause of acute onset carpal tunnel symptoms.
Diagnosing a Perilunate Injury
A perilunate injury can be seen on a regular X-ray. However, the appearance of a perilunate dislocation can be subtle, especially if the X-rays are done with the hand slightly rotated. When people have severe injuries, getting good X-rays can be uncomfortable and difficult. However, it is important to have proper X-rays to evaluate for injuries such as a perilunate dislocation.
A CT scan or MRI can be helpful if there is a question of the diagnosis. Furthermore, perilunate dislocations can occur as part of a group of injuries including fractures and ligament tears. Further studies may be performed to evaluate for other injuries in the wrist.
The lunate bone is shaped like the crescent moon and it is located where the two arm bones—the ulna and the radius—meet the other carpal bones of the wrist. The lunate can have a variable shape, so your lunate may not look like a typical one even when not injured. Lastly, perilunate injuries are often associated with severe traumatic injuries, and other, potentially life-threatening injuries may take attention away from a wrist injury. For these reasons, perilunate injuries can be missed on an initial examination, and people with signs of this problem should be assessed.
What Is the Treatment of a Lunate Dislocation?
It is important to reposition the lunate bone so that it is properly oriented as soon as possible. Sometimes this can be done in the emergency room, but often this needs to be treated surgically. Even if the lunate dislocation can be repositioned non-surgically, a surgical procedure is usually required to stabilize the bones to allow for proper healing.
Perilunate dislocations are usually held in place using pins that come through the skin for later removal in the office. A carpal tunnel release may be performed at the time of surgery if there were symptoms of carpal tunnel syndrome. Additionally, surgery may address other fractures and ligament tears that occurred at the time of the injury.
Complications are common after sustaining a perilunate dislocation, and the long-term prognosis for people who sustain this injury is guarded. These problems can include wrist arthritis, persistent pain, stiffness of the joint, and instability of the carpal bones. Prompt treatment helps to lower the chance of these complications, but they are still common. Recovery from a perilunate dislocation will take a minimum of 6 months, if not longer, and mobility and strength generally do not return to normal.