Variations of Capitate Morphology in the Wrist

Purpose: This anatomical study details and categorizes variations in capitate morphology and associated structures in the human cadaveric wrist. Methods: We dissected 107 cadaveric wrists. Capitate morphology, the presence of capitate and hamate ridges, the lunate types, and the width of the medial hamate facet of type II lunates and 4th carpometacarpal joint types were recorded. Results: Three types of capitate were identified. The flat type (69/107, or 65%) was characterized by a horizontally oriented (radio-ulnar) lunate-capitate articulation and a longitudinally oriented (proximal-distal) scaphoid-capitate articulation. The flat type was associated with type I lunates or type II lunates with a smaller facet. The spherical type (23/107, or 22%) was associated with a concave articulation formed by the scaphoid and lunate articulations, with an indistinct border between the scaphoid and lunate facets. The width of the medial hamate facet of type II lunates in wrists with a spherical-type capitate was ≤4 mm. The V-shaped type (15/107, or 14%) was characterized by separate lunate and scaphoid facets that converge, forming a V-shape. All the V-shaped capitates had a type II lunate with a large facet. Conclusions: A relationship was found between the 3 capitate types and both the lunate types and the width of the medial hamate facet of the type II lunates. Further study is warranted to determine if these differences in capitate morphology influence the development or progression of various wrist pathologic conditions, such as Kienböck's disease and post-traumatic arthritis associated with scapholunate dissociation and scaphoid nonunion, and the outcome of certain surgical procedures, such as a proximal row carpectomy.