Accuracy and reliability of indices for assessing proximal interphalangeal joint position in hammer toes

Introduction
Hammer toes are among the most common toe deformities. Aim of the research: This study evaluated the accuracy and measurement reliability of the six indices proposed by the authors for assessing deformities typical of hammer toes.

Material and methods
We examined 30 persons with hammer toes, aged 65–74 years. Measurements were compared using a GIMA anthropometric tape (Gima S.p.A., Gessate (MI), Italy), Beerendonk HOSSA caliper (Hossa Int., Sialkot, Pakistan), Xiaomi Redmi 5 smartphone camera (Xiaomi Inc., Beijing, China), and the GIMP application. The results were analysed using the Wilcoxon test and factor analysis. A test-retest measures design was utilised, with the intraclass correlation coefficient (ICC) used to determine levels of reliability.

Results
The index of height of the proximal interphalangeal joint (H1), and the index determining the difference in the height of the examined joint compared to interphalangeal joint of the big toe (H3), achieved the maximum factor loading values (–0.831 and 0.820, respectively). The values of intraclass correlation coefficients for all assessed indices exceeded 0.90, with the highest values recorded for the α angle (ICC = 0.99) and the H1 index (ICC = 0.98).

Conclusions
Proposed indices for testing the position of the proximal interphalangeal joint in hammer toes meet the accuracy criterion, with the H1 index being the most accurate for testing the absolute height of this joint, and the H3 index for testing the relative height. All proposed indices meet the criterion of reliability of measurement results, and therefore they can be used in clinical studies to assess the position of the proximal interphalangeal joint in hammer toes.