Mbalenhle Mandisa Mvundla; Samuel Oluwaseun Olojede; Sodiq Kolawole Lawal; Edwin Coleridge Naidu & Onyemaechi Okpara Azu

The dorsal interosseous muscles (DIM) are intrinsic muscles of the hand located dorsally between metacarpal bones, which play a role in finger abduction. Anatomical variations of these muscles in terms of form and length have been well documented, but variations regarding sex and laterality are underexplored. The aim of this study was to investigate the morphology and morphometry of the DIM of the hand regarding sexual dimorphism and laterality. Twenty human cadavers belonging to the white individuals (n = 40 hands) with known sex and laterality were used for this study. DIMs were dissected and observed for morphology. Also, a digital calliper was used to measure the midpoint length of the DIM. The origin and insertion of all the DIM were normal with the left hand having no additional, supernumerary, and absent muscles in each compartment. The variations were only found on the right side and predominant in females: 2 out of 11 (18.18%) hands containing a space with a supernumerary muscle; 1 out of 11 (9.09%) hands having a space with a double muscle; and 1 out of 11 (9.09%) hands having a compartment with a unipennate muscle. In males, 1 out of 9 (11.11%) hands had a compartment with a supernumerary muscle. The mean midpoint length of each muscle in females and males in both hands from the first to the fourth muscle, respectively, was documented. In females on the left: 46.79 ± 3.56; 42.62 ± 3.57; 49.02 ± 4.21; 41.66 ± 2.15 and right: 47.30 ± 2.49; 39.27 ± 4.14; 45.69 ± 4.64; 38.12 ± 4.08. In males, it was on the left: 50.01 ± 3.95; 41.98 ± 3.79; 47.90 ± 4.83; 41.79 ± 4.25, and on the right: 46.65 ± 2.09; 39.01 ± 4.25; 47.47 ± 3.41; 38.31 ± 4.40. The mean midpoint length of the DIM was relatively higher on the left hand compared to the right hand in both females and males. In this study, variations regarding the supernumerary muscle, double interosseous space, and unipennate muscles were only observed on the right-hand side and predominantly in females, an insight that may guide in the treatment of fractures, stiffness of the hand, and compartment syndromes.

KE WORDS: Dorsal interosseous muscle; Morphology; Morphometry; Variations; Sex; Laterality.