New connective tissue structure of the wrist area - research on fetal material.

The correct function of the upper limb depends on the cooperation and coordination of the muscular and skeletal systems as well as the connective tissue elements present in it. Connective tissue forms fascia, connective tissue membranes and ligaments. Connective tissue mostly develops from the mesenchyme. It is formed from the intercellular substance consisting of protein fibrous elements and the ground substance. The fibrous elements generally fulfill the mechanical function of the intercellular substance. There are three types of fibrous elements: collagen fibers, reticular fibers and elastic fibers. The aim of the study was to examine the occurrence of fibrous structures in the wrist area in fetal material stored in the Prenatal Laboratory of the Department of Anatomy of the Wroclaw Medical University (Wroclaw, Poland). The research included 114 fetuses (53 male and 61 female) of between 117.0 and 197.0 (median 177.0) days of fetal life. The study showed 100% prevalence of a ring-shaped connective tissue structure on the radial side of the wrist located around the tendon of the "flexor carpi radialis muscle", previously unobserved in fetuses. Its bilaterality was found in 57.9% and unilaterality in 42.1% of the examined fetuses. In male fetuses, the ring-shaped structure was located in the right upper limb in 68.9% of the examined limbs, and in the left in 80.3%. Bilaterality was 49.2%, and unilaterality 50.8%. In female fetuses, this structure was observed in the right limbs in 84.9%, and in the left in 77.4%. Bilaterality was 61.1%, and unilaterality 38.9%. The structure that was observed has not been described in fetuses so far; only in one study authors describing a similar change in adults calls it an "Annular Pulley" and connects its significance with the system of disc-shaped ligaments of the tendons of the flexor muscles of the hand, which are an element of the attachment system of tendons to the skeletal system. Its function within the ligamentous and retinacular system of the wrist remains unknown. This is the first study to describe the occurrence of the "AP" in fetal material. Further research is required to understand its role in the biomechanics of the upper limb and its histological structure.