Investigating Normative Measurements of the Thumb and Index Finger to Aid in Reconstructive Surgery.

Purpose: This study aims to investigate normative measurements of the thumb relative to the index finger; this may help guide hand surgery reconstruction and define a thumb as hyperplastic or hypertrophic. Methods: In total, 162 Minnesota State Fair participants were measured for thumb and index finger length, width, girth; joint range of motion (ROM) of the interphalangeal and metacarpophalangeal joints; and pinch and grip strength. Results: Participants' age averaged 42.5 (range 14-88) years with 57% female, 86% White, and 86% right-handed. The right and left demonstrated similarity of thumb and index finger size for each participant. Men demonstrated larger length and girth of the thumb and index finger and stronger pinch and grip strengths but have minimal differences in ROM compared to women. The ratio of the index fingernail is 75% of the thumbnail. The length of the thumb is 73% of the index finger, and the thumb interphalangeal girth is 80% of the index finger proximal interphalangeal (PIP) joint. On average, the thumb tip sits 1.9 cm proximal to the index PIP joint. Conclusions: Anthropometric measurements of the thumb and index fingers demonstrate similarities of right and left hands for length, girth, ROM, and strength. Differences exist with size and strength greater for men compared with women, without differences in ROM. The thumb tip, on average, sits 19 mm proximal to the PIP joint, which is contrary to the conventional teaching for index pollicization to set the thumb tip length to the level of the adjacent finger PIP joint. Type of study/level of evidence: Therapeutic IV.