An Analysis of Hamate Morphology Relevant to Hemi-Hamate Arthroplasty

Dorsal fracture-dislocations of the proximal interphalangeal (PIP) joint can lead to joint incongruity from loss of the buttress function of the middle phalanx volar base. Hemi-hamate arthroplasty can reconstruct the volar articular surface of the middle phalangeal base where repair is not possible. We compared the anatomy of the hamate graft with the middle phalanx base.

Forty unique skeletal specimens (40 hamates, 160 middle phalanges) were sampled. Anatomical features relevant to hemi-hamate reconstruction were measured, including the articular surface areas, the axial ridge angles, and the sagittal inclination angles of the hamate and the middle phalanx base specimens. Facets of the articular surfaces were classified as concave, convex, or flat. Calibrated measurements were made using digital photographs of the cadaveric specimens. Descriptive and univariate statistics were performed.

There was greater variability in the distal hamate than in the middle phalanx base. The ring finger facet of the distal hamate was concave in 39 of 40 specimens, whereas the little finger facet was convex in 31 of 40 specimens. The hamate axial ridge angle (66.0° ± 3.7°) was significantly different from the middle phalanx base (90.4° ± 0.4°). The hamate articular sagittal inclination (3.2° ± 4.1°) was significantly different from the middle phalanx base (51.2° ± 1.3°). The hamate articular surface area (1.96 cm²) was significantly greater than the middle phalanx base (mean index/middle/ring finger = 0.85 cm² and mean little finger = 0.59 cm²).

The distal articular surface of the hamate is not anatomically identical to the middle phalanx base. The differences may still preclude anatomical reconstruction in the setting of a dorsal PIP fracture-dislocation, thereby affecting short- and long-term outcomes.

Knowledge of the anatomical differences between the distal hamate and the middle phalanx base may improve graft harvest and inset during reconstruction.