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Lunate Bone

os lunatum

The lunate is the central carpal bone in the proximal row, articulating with the radius proximally, the capitate distally, the scaphoid radially, and the triquetrum ulnarly. Its blood supply enters through dorsal and palmar perforating vessels with variable anatomy: in approximately 20% of individuals only dorsal vessels supply the lunate (type I), predisposing to AVN (Kienbock disease) when these are disrupted. The lunate has two morphological variants: Type I (no medial facet for hamate) and Type II (medial facet for hamate, associated with lunohamate impingement).

Region: Hand & Wrist

Clinical Relevance

Clinical Notes

Kienbock disease (lunate AVN) is associated with negative ulnar variance (shorter ulna than radius) which concentrates radial load on the lunate. Staging by Lichtman (I-IIIb with IIIB including DISI) guides treatment from joint levelling (radial shortening osteotomy for negative UV) through scaphocapitate fusion to wrist salvage procedures. The Type II lunate morphology predisposes to lunohamate impingement syndrome, a distinct wrist pain condition from lunate-hamate cartilage damage.

Pathology

Common Injuries & Conditions

Kienbock Disease — Lunate Avascular Necrosis

Repetitive compressive stress and relative radial overloading in negative ulnar variance produces lunate AVN with progressive sclerosis, fragmentation, and collapse visible on radiograph and graded by MRI; radial shortening osteotomy to neutralise ulnar variance in early disease reduces lunate loading and halts progression in the majority of patients.