Assessing Rotational Deformity of the Little Finger

Materials and Methods

Study patients were healthy volunteers. Any individual with a history of finger or hand trauma, arthritis of the hands, or any other known deformity of the nails or fingers was excluded. To ensure clinical reproducibility, a digital camera with a Canon (5.8–17.4mm lens; Lake Success, New York) was mounted on a tripod and set at a distance comparable to the eye level of a practitioner (45 cm). Photographs of each individual’s hands were taken with the fingers in extension to measure the nail width of the little finger (Figure ). A second photograph was obtained with the metacarpophalangeal and proximal interphalangeal joints in flexion (Figure ). To observe the fingers in extension, the patients placed their hands in approximately 90° of pronation with their palms resting on a flat surface. For analysis in flexion, hands were placed in 90° of supination with the dorsal aspect of the hand resting on the same flat surface. The digital images were uploaded to a computer and analyzed by 2 independent observers (P.J.L., M.R.P.) using ImageJ (NIH, Bethesda, Maryland) software to measure both the width of the little fingernail in extension and the degree of overlap in flexion. The degree of overlap was quantified by the percentage of nail obscured by the adjacent finger.

Figure 1:. Fingers in extension.

Figure 2:. Fingers in flexion.

The mean and standard deviation were calculated for percentage of overlap and chi-square analysis was used to test for significance between groups. The average difference between left and right hands in each individual was also analyzed. A P value of <.05 was considered significant. The Kappa coefficient was calculated to measure interobserver reliability between the 2 authors.

Results

Forty patients met inclusion criteria and had measurements made of both hands. The 23 men and 17 women had an average age of 35.9 years (range, 22–69 years). Seven patients were left-hand dominant. Seventy of 80 hands had at least partial overlap of the little finger, and 37 of 40 patients showed asymmetric overlap between left and right hands. The average variation between hands in individuals was 16%±13%. The average little finger fingernail overlap was 25%±20%, ranging from 0% to 71%. The average overlap on the left was 20%±18% as compared to 30%±21% for right hands. This difference was statistically significant ( P<.01). The Kappa coefficient calculated was 0.82, reflecting substantial agreement between the 2 authors performing measurements.

Discussion

Malrotation of the little finger is an indication for surgery for metacarpal and phalangeal fractures since it can lead to overlap and impaired function. A number of different methods have been described to assess malrotation. Scissoring or overlap at the fingertip with the metacarpophalangeal and proximal interphalangeal joints flexed, particularly when compared to the contralateral hand, is a well-known technique. ¹

While testing with the distal interphalangeal in flexion may offer additional functional information, it would be impossible to assess fingernail overlap in this position. As a result, testing was done with the distal interphalangeal joint in extension to reproduce this common and accepted clinical examination. However, it can be painful for a patient to make a fist with a fracture.

Tan et al ⁴ showed that end-on examination of the fingernails in extension or flexion is somewhat problematic. Their study showed that in normal patients, fingernails are neither horizontal nor parallel to each other and the little finger is the most supinated in both extension and flexion with a range of 30° (-5° to 25°). In addition to substantial variation in the alignment of the fingernails within a hand, significant asymmetry of nail inclination between the 2 hands also exists. In another study evaluating nail inclination, 20% of fingernails did not match within 5°, and nearly 5% did not match within 10°. ⁵

We challenge the traditional thinking that normal individuals have no overlap when testing for scissoring. In this study, we found that scissoring is not only common, but actually the norm, with 70 of 80 hands exhibiting some degree of little finger overlap. The large variability of overlap and the frequent asymmetry in these normal patients demonstrate that scissoring, even when compared to the contralateral hand, may not reliably demonstrate malrotation. We found the average difference in overlap of the little finger to vary significantly. This has implications not only in assessing patients for possible surgery, but also in planning and performing surgical reductions of acute fractures and for correction of malunions.

This study is somewhat limited by the fact that small variations in the position of the hand under the camera could have affected the amount of overlap recorded. Efforts were made to standardize hand positions while attempting to mimic a clinical examination. Functional tests were also not performed to determine if any of our normal patients had any functional deficit from their overlapped little fingers. While it is possible the variation between left and right hands found during data analysis may be attributed to hand dominance, that analysis goes beyond the scope of our study.

The practitioner must be aware of the variation among the population as well as the individual when determining the treatment for a patient with little finger pathology.