A new alternative to quantify finger rotation: angles between the axis of flexed fingers and the axis of third metacarpal bone.

Objective: To determine whether the proposed angle, formed between the axis of middle and distal phalanges of each of flexed fingers and the axis of the third metacarpal bone was symmetrical between both hands in adult population.

Material And Method: Thirty-one volunteers (12 males and 19 females) having normal and uninjured hands with an average age of 38 years underwent a fluoroscopic examination of their hands. All volunteers put their hands in a special positioning device that passively held the metacarpophalangeal and proximal interphalangeal joints in full flexion with distal interphalangeal joint in full extension. Fluoroscopic images were then taken and angles were digitally measured.

Results: Mean angles of the flexed index, middle, ring and small fingers compared to the third metacarpal bone were -4.07 (SEM = 1.041), 5.22 (SEM = 0.889), 12.91 (SEM = 1.009) and 23.11 (SEM = 1.370) degrees, respectively. The angles were statistically symmetrical between both hands (p = 0.838, 0.546, 0.620 and 0.641, respectively). The genders had no effect on the symmetry (p > 0.3). The differences between angle of each finger and the angle of the middle finger were also found to be statistically symmetrical.

Conclusion: Side-to-side comparison of the angle formed between the axis of flexed fingers and the third metacarpal bone measured from radiographic images can be used as an additional alternative to determine the finger rotation. The angular relationship between each finger with respect to the middle finger can also be used to purposefully reduce x-ray beam projection variation.