MORPHOMETRIC ANALYSIS OF HUMERAL SHAFT DIMENSIONS AND TORSIONAL ANATOMY

Abstract

The humerus, the longest bone of the upper limb, demonstrates significant anatomical variation, particularly in its length and rotational features. While maximum humeral length (MHL) and humeral biomechanical length (HBL) are commonly used in anthropometry and orthopedics, the humeral torsion angle (HTA) plays a vital role in shoulder mechanics and joint orientation. However, the interrelationship between these parameters remains underexplored. This study aims to assess the morphometric relationship between MHL, HBL, and HTA in adult human humeri and to determine whether humeral length influences torsional alignment. A total of 36 dry adult humeri (16 right-sided and 20 left-sided) were selected from the osteological collection of the National Institute of Ayurveda (NIA), Rajasthan. MHL, HBL, and HTA had been measured using standard osteometric procedures and digital imaging. Descriptive statistics and Pearson’s correlation coefficient were used to evaluate relationships among the parameters. The mean MHL was 30.99 ± 1.56 cm, HBL was 30.57 ± 1.51 cm, and HTA was 64.08° ± 9.23°. A very strong positive correlation was found between MHL and HBL (r = 0.99, p < 0.001), whereas weak, non-significant correlations were found between MHL and HTA (r = 0.10, p = 0.565) and between

HBL and HTA (r = 0.12, p = 0.479). Side-wise analysis revealed significantly greater MHL and HBL values in right-sided humeri compared to the left (p < 0.01), while HTA did not significantly differ between sides (p = 0.991). Side-related correlations between length parameters and HTA remained weak and statistically not significant. While MHL and HBL are closely related morphometric indicators, neither shows a significant influence on the humeral torsion angle. These findings suggest that torsion is anatomically and functionally independent from shaft length, emphasizing the need for individual assessment in clinical and surgical planning. Additionally, the detected side related asymmetry in humeral length parameters highpoints possible influences of limb dominance or usual use, while the consistent torsional values across sides emphasize the age-related stability of HTA as an independent anatomical trait.