A type II lunate, on the other hand, has an extra articulation medially with the hamate at its medial or hamate facet. About 50% of lunate bones have a hamate facet.
The hamate and type II lunate rub up against each other during full ulnar deviation of the wrist. This is thought to be the reason that patients with type II lunates have a greater propensity for development of focal chondromalacia and osteoarthritis of the proximal pole of the hamate. About 25% of patients with type II lunates have chondromalacia along the proximal pole of the hamate that is often occult on MRI.
The case shown here shows a type II lunate, no marrow edema in the hamate, and some fluid within the hamatolunate space. Also seen is a multiseptated intraosseous ganglion with associated cortical irregularity in the proximal pole of the lunate at the scapholunate ligament attachment.
References
- Malik AM, Schweitzer ME, Culp RW, Osterman LA, Manton G. MR imaging of the type II lunate bone: frequency, extent, and associated findings. AJR Am J Roentgenol. 1999;173(2):335-8.
- Cerezal L, del Piñal F, Abascal F, García-Valtuille R, Pereda T, Canga A. Imaging findings in ulnar-sided wrist impaction syndromes. Radiographics. 2002; 22(1):105-21.
Nice picture.
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