Opponens pollicis in fetuses: classifications, measurements, and clinical implications

A fetal investigation on the anatomical properties of opponens pollicis was not encountered in the literature in terms of surgical procedures performed in the early childhood period. In this context, this study aimed to examine the origin, insertion, and morphometric characteristics of opponens pollicis in human fetuses. Fifty-two sides of 26 fetuses (mean age: 24.08±4.22 weeks, sex: 11 males and 15 females) were dissected. The origin and insertion of the opponens pollicis were noted. The area, length, and width of the opponens pollicis were measured with the surgical microscope. Furthermore, according to the literature review, the origin and insertion of opponens pollicis were classified as seven and four types, respectively. The mean width, length, and area of the opponens pollicis were found as 3.28±1.15 mm, 7.12±2.44 mm, and 20.45±16.14 mm2, respectively. In this study, opponens pollicis most commonly started from the flexor retinaculum plus the tubercle of the trapezium (22 sides) and ended on the anterolateral side of the first metacarpal bone (41 sides). Fetal information related to morphometric characteristics and variations of opponens pollicis may be important for clinicians in reconstructive interventions on the thumb muscles in the early childhood period. Our classifications performed for the first time in the literature may guide future studies, especially those focused on thumb anomalies such as polydactyly and syndactyly.