[The axial orientation of the phalanges following the curling up of the fingers]

Rotations of three-joint fingers: a radiological study

The aim of the current study was to test a protocol of quantification of phalangeal three-dimensional (3D) rotations during flexion of three-joint digits. Three-dimensional-specific software was developed to analyze CT reconstruction images. A protocol was carried out with six fresh-frozen upper limbs from human cadavers free from any visible pathology (three females, three males). CT millimetric slices were done for reconstruction of hand bone units. Orthonormal coordinate systems of inertia were calculated for each unit. Three-dimensional phalangeal rotations were estimated between two static positions (fingers in extension and in a fist position). Results were displayed for the joints of each three-joint finger with calculation of 3D rotations. Mean longitudinal axial rotations of metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints ranged from 14 degrees pronation to 19 degrees supination. The index finger was in a global pronation position (4/6 specimens). The fourth and fifth fingers were in a global supination position in every case. The third finger was in a more variable global rotation (pronation in 2/6 specimens). MCP, PIP and DIP flexion angles ranged respectively from 71 degrees to 89 degrees, 65 degrees to 87 degrees, and 41degrees to 77 degrees. Lateral angles ranged from 19 degrees (ulnar angulation) to 23 degrees (radial angulation). The study of phalangeal rotations was possible in spite of a heavy protocol. This protocol could be partially automatated to speed up the analyses. Longitudinal axial rotations could be analyzed, in addition to flexion/extension or abduction/adduction rotations. CT scan reconstructions would be helpful for investigating pathological fingers. Abnormal rotations of digits could be quantified more precisely than during a current clinical examination of the hand.