A Cadaveric Study of Morphological Variations of the Abductor Pollicis Longus Muscle and Its Tendinous Insertions.

Abstract

This study examined the abductor pollicis longus (APL) and abductor pollicis brevis (APB) muscles, which are key muscles involved in thumb abduction and fine motor function, with anatomical variations of the APL particularly accessory tendons implicated in the pathogenesis of De Quervain's tenosynovitis by contributing to crowding within the first dorsal compartment. This cadaveric observational study was conducted at the Department of Anatomy in collaboration with the Department of Physiology, All India Institute of Medical Sciences, Gorakhpur, India, using twenty prosected upper limbs from voluntarily donated cadavers of Indian origin (10 rights and 10 lefts). Morphological parameters recorded included tendon length, width, attachment patterns, presence of accessory APL (a-APL) and APB variations, while biomechanical measurements included fascicle length, pennation angle and muscle mass, with physiological cross-sectional area (PCSA) and maximum force (Fmax) calculated using standard biomechanical formulas. All 20 specimens demonstrated a normal APL muscle belly and tendon; accessory APL tendons were identified in 70.0% of specimens, with 8 right-sided and 6 left-sided occurrences. Mean ±SD tendon length of APL was 62.8±17.41 mm on the right and 71.0±19.84 mm on the left, while mean width was 2.3±0.59 mm and 2.6±0.52 mm, respectively. A rare anatomical variation was observed in one specimen where APB originated from the accessory APL tendon. Biomechanical analysis showed APL had a PCSA of 3.27 cm² and predicted Fmax of 114.45 N, whereas APB demonstrated a PCSA of 1.42 cm² and Fmax of 49.70 N. These findings confirm that accessory APL tendons and atypical APB origins are common anatomical variants with significant clinical implications in De Quervain's tenosynovitis and that integration of morphometric and biomechanical data can enhance surgical decompression strategies, rehabilitation planning, ergonomic counseling and evidence-based nursing care.