Obturator Externus Muscle - Variation

Variation

In 33% of people a supernumerary muscle is found between the adductor brevis and minimus. While this muscle, when present, is similar to its neighbouring adductors, it is formed by separation from the superficial layer of the obturator externus, and is thus not ontogentically related to the adductor muscles of the hip. This muscle originates from the upper part of the inferior ramus of the pubis from where it runs downwards and laterally. In half of cases, it inserts into the anterior surface of the insertion aponeurosis of the adductor minimus. In the remaining cases, it is either inserted into the upper part of the pectineal line or the posterior part of the lesser trochanter.

It has been demonstrated by the course of the posterior branch of obturator nerve that the obturator externus is divided into a superior fasciculus and a main belly. The supernumerary muscle described above originates from the superior fasciculus, while an anomalous fasciculus — also derived from the obturator externus — originates from the main belly. The "original" obturator externus, i.e. without these supernumerary muscular parts, actually occurs in only 20% of cases, and apparently the obturator externus readily undergoes ontogenetic variations.