Located in the wrists and named for the bones it helps stabilize, the scapholunate ligament holds together the scaphoid bones and the lunate bones, which are the lower two bones in the wrist that sit adjacent to the radius and ulna, the bones of the forearm. These two wrist bones are known as the proximal carpal row. The scaphoid bone is located on the thumb side of the wrist, and the lunate bone, which is slightly crescent- or moon-shaped, lies next to it on the little finger side. A major function of the scapholunate ligament is to stabilize these bones, holding them in place to allow palmar rotation and other complex wrist movements. It consists of three parts — the dorsal, palmar and proximal — with the strongest of these being the dorsal area.
One form of wrist injury is a strain, rupture or tear of the scapholunate ligament, which usually occurs when the patient falls on an extended hand, placing a great deal of force and pressure on this important wrist ligament. Rupturing the scapholunate ligament can allow the bones to move out of position, resulting in long-term wear on the other bones of the wrist, which leads to long-term wrist pain. This is known as scapholunate instability because the scaphoid and lunate bones are no longer stable within the wrist. In some cases, scapholunate ligament instability can be seen easily on X-rays because the bones move significantly out of place, but in other cases, the bones do not move as dramatically, and the instability is more difficult to diagnose because the bones remain close to their original, normal alignment.
Discovering damage to the scapholunate ligament early is important for successful treatment, whether this is simply to observe the wrist over a period of time or to pursue more invasive treatment such as surgery. Some symptoms include wrist pain or tenderness, weakness in the wrist or a clicking sound in the bones of the wrist. If the tear to the scapholunate ligament is treated early enough, it can heal, though long term effectiveness of various treatments is not guaranteed and often result in reduced wrist flexibility. Different surgical approaches include reconstructing the scapholunate ligament from adjacent tissue and temporarily wiring the two bones together while the ligament heals. However, if the injury is left untreated, eventual solutions might require fusing the small bones of the wrist to prevent continued abrasion between them and even more severely impacting overall wrist flexibility.