Measurement of Rotation of the First Metacarpal During Opposition Using Computed Tomography

PurposeOpposition is an important movement of the hand and rotation of the first metacarpal is the essential component. There is no agreement on the exact magnitude of rotation of the first metacarpal during opposition. This study used computed tomography to describe rotation measurement of the first metacarpal in the hands of a group of healthy individuals.MethodsThe rotation of the first metacarpal was measured with reference to the fixed unit of the hand. Computed tomographic images were taken of the hands of 10 healthy individuals with the thumb in retroposition, resting position, and opposition to the index, middle, ring, and small fingers. On each image a tangential line was drawn along the dorsal margin of the second and third metacarpals. A second line was drawn through the head of the first metacarpal at the level of the sesamoids. The angle between the 2 lines was measured as the angle of rotation of the first metacarpal in different thumb positions.ResultsThe mean angle of rotation of the first metacarpal in retroposition was 54° ± 10° with reference to the fixed unit of the hand. In the resting position the angle of rotation of the first metacarpal changed to 74° ± 10°. In the position of opposition to the index, middle, ring, and small fingers the angle of rotation of the first metacarpal increased to 100° ± 7°, 103° ± 6°, 105° ± 6°, and 110° ± 7°, respectively.ConclusionsThe first metacarpal rotates 56° when it moves from retroposition to the position of opposition to the small finger.