In this special focus article featuring the hand and wrist, hand surgeons from the New York University Hospital for Joint Diseases present information on perilunate injuries. They discuss the complex anatomy of these injuries, management, and two important factors that affect long-term outcomes. Information is presented from their review of the latest research on this subject.
The word perilunate means “around the lunate” (wrist bone). The lunate carpal (wrist) bone is neatly tucked in between the two bones of the forearm, the two other carpal bones on either side, and another row of carpal bones next to the fingers.
It doesn’t dislocate easily and usually only after significant high-energy trauma. Falling off a bike and hitting the pavement could certainly cause this type of injury. Car accidents and sports injuries account for the majority of lunate injuries.
Dislocation of this bone usually means the soft tissues around the lunate have been disrupted. There are four steps or “stages of injury” that occur to force the lunate out of place. It’s a bit like dominoes — once the first one goes, a whole series of events takes place.
In stage one, the carpal bones next to the fingers are forced into a position of extreme extension. The ligaments around those bones pull the scaphoid bone of the wrist (the bone next to the lunate on the thumb side) into a position of extension. The ligament between the scaphoid and lunate tears. The force of the injury continues to transfer through the wrist to the ligaments around the lunate. That is stage two of the sequence.
In stage three, the lunate dislocates and pulls with it the ligament between the lunate bone and the triquetrum (bone on the little finger side of the lunate). And then in stage four, the ligament between the radius bone of the forearm and the lunate tears allowing the lunate to rotate or twist and dislocate.
Of course, all of these events occur in a matter of seconds starting at the moment of impact. The loss of the ligament stability and shift in bone alignment changes the whole structure and dynamics of the wrist. The natural “arcs” or archways formed by the two rows of carpal (wrist) bones is affected. This can put pressure on the nerves that travel through the arcs. And in a perilunate injury, any of the bones around the lunate can be fractured, dislocated, or both.
Treatment is usually aimed at putting the bone(s) back in place (a process called reduction). In some cases, this can be done manually (by hand as the surgeon gently manipulates the bones) while the patient is asleep under anesthesia. Pressure on the nerve or inability to reduce the bones may point to the need for open surgery. The surgeon assesses the damage and repairs any torn ligaments using wires or screws to hold the bones in place until healing occurs. The procedure is called open reduction and internal fixation or ORIF.
There are many different ways to do this surgery. No one method has been identified as the best or only way to do it. The authors of this review discuss the various surgical techniques and offer their opinions based on what the literature says and their own experiences. Types of incisions, approach (from the front of the wrist, back of the wrist or combination of the two), and open versus arthroscopic repair are a few of the decisions the surgeon must make.
The last important message of this article has to do with factors affecting results of treatment. These include: 1) timing of treatment (how soon surgery is done after the injury) and 2) quality of the reduction (how well the bones are lined up and stabilized). A delay of more than a month can mean worse results than with early treatment. Even with the best treatment early on, patients can expect some loss of grip strength and motion.
Severe injuries with less than ideal alignment can mean early arthritic changes. But most of these injuries do heal. Patients are able to resume daily activities and even return to work. Manual laborers have greater difficulty with return to full work activities and often report worse outcomes. Patients who are treated surgically using both the front (volar) and back (dorsal) wrist incisions tend to have decreased results as well.