IS Case 421: Type II lunate
Imaging Sciences URMC 2010
Publication Date: 2010-08-27
Plain films in PA and lateral projections of the right wrist demonstrate several findings, including advanced osteoarthritis of the 1st carpometacarpal joint, scapholunate dissociation with erosion of the scaphoid through the distal radius, osteopenia and soft tissue swelling of the dorsal aspect of the wrist. However, an incidental note is made of a type II lunate with associated moderate degenerative changes of the lunohamate joint.
Type II lunate
The lunate bone is an integral component of wrist joint mechanics. It is named for the curvilinear shape of its articulation distally with the capitate, and is classically described as articulating proximally with the radius and ulna, laterally with the scaphoid, and the triquetrum medially. A type II lunate has an accessory facet articulating with the hamate and is associated with degenerative disease. One study using MR defined type II lunate as a lunate with a distinct concavity opposing the hamate on at least 10% of the coronal sections through the lunate.
Presence of a type II lunate has been associated with secondary focal chondromalacia and osteoarthritis, occurring at the articulation of the lunate and hamate. In one study 45% of patients with type II lunate were found to have chondromalacia or arthrosis of the proximal hamate while no patients with a type I lunate had such complications. These findings can be attributed to alteration of the normal kinetic and loading mechanics of the lunate caused by the extra facet joint.
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- Viegas SF, Wagner K, Patterson R, Peterson P. Medial (hamate) facet of the lunate. J Hand Surg Am. 1990 Jul;15(4):564-71. PMID: 2380518 [PubMed]