Variation in digital rotation and alignment in normal subjects.

PURPOSE

The purpose of this study is to quantify finger/digit rotation, overlap, parallelism, and convergence to the scaphoid tuberosity in normal volunteers to establish standards for comparison.

METHODS

We examined 240 uninjured fingers in 30 volunteers. There were 14 men and 16 women with an average age of 35 years. Rotation was determined with the palm flat and fingers extended. Digit overlap, parallelism (angular relationship between the index, ring, and small fingers with respect to the middle finger) and scaphoid convergence were determined with simultaneous flexion of metacarpophalangeal and proximal interphalangeal joints. Linear and angular measurements were performed with imaging software.

RESULTS

Rotation, parallelism, and scaphoid convergence measurements were similar comparing left with right hands. Rotation: All digits were found to be in supination relative to the horizontal plane; the small fingers averaged 9 degrees, the ring fingers 4 degrees, the middle fingers 8 degrees, and the index fingers 12 degrees. Parallelism: Angular measurements between the middle finger and the small finger averaged 19 degrees, between the middle finger and the ring finger 9 degrees, and between the middle finger and the index finger 11 degrees. Scaphoid convergence: In no hand did all 4 fingers converge onto scaphoid tuberosity. Whereas small and ring finger trajectories averaged -0.1 to 1.2 mm from the scaphoid tubercle, the middle finger averaged 4.0 to 4.6 mm and the index finger 8.1 to 9.5 mm. Overlap: Ninety percent of individuals demonstrated digit overlap, although none covered more than 50% of the adjacent nail plate. Seventy-seven percent of these were bilateral, and 73% were asymmetric.

CONCLUSIONS

This study establishes the normal parameters for digit rotation, overlap, parallelism, and scaphoid convergence. For digit rotation, parallelism, and scaphoid convergence, the contralateral (uninjured) hand can be used reliably for comparison. However, for digit overlap, the contralateral hand should not be used for comparison because of side-to-side asymmetry and variability.

TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic IV.