Lunotriquetral Instability

Excerpt

Lunotriquetral (LT) joint instability is an often missed diagnosis and can result in LT dissociation. The reasons for undiagnosed LT joint instability are in part due to multiple confounding injuries (usually associated with high energy/impact sports) and isolated injury to the LT ligament results in relatively normal-appearing radiographs. LT ligamentous injury is less common than other proximal, carpal row, ligamentous injury and thus, more poorly understood and diagnosed.

The earliest reported LT injury was in 1903, which was then followed by a description of carpal dissociation of the lunate and triquetrum without significant change in position in 1913. Later in the 1900s, volar intercalated segmental instability (VISI) began to be defined. In the mid to late 1900s, it was found that a cause of VISI was LT ligament dissociation.

The wrist is comprised of numerous extrinsic and intrinsic ligaments that work together to provide stability. The complex, harmonious relationship between these ligaments indicates that compromise in the integrity of one of these parts will affect the overall position and strength of the wrist. The extrinsic ligaments that are most often involved in LT instability include the dorsal radiocarpal (providing dorsal support) and the radiolunate ligament (providing volar support). The interosseous LT ligament is the main intrinsic ligamentous supporter of the LT joint. It is described as “C” shaped and is divided into 3 parts. The volar portion is the strongest and thickest portion and provides the most stability and mainly prevents volar translation. The dorsal portion limits rotational movement, and the combination of all parts of the LT intrinsic ligament prevent dorsal translation. Both of these attach to bone, while the third, weaker portion, or membranous portion, connects to the articular cartilage. The dorsal radiocarpal ligament is an extrinsic ligament that when injured will cause further instability of the LT joint by allowing the lunate to flex more easily. The radiolunate ligament is extrinsic and can be involved in advanced cases of injury.

The lunate and triquetrum have been shown to have the same movements in flexion/extension motion as well as radial/ulnar deviation. This is likely why the lunotriquetral coalition is usually an asymptomatic variant.