The PM passes posterior to the nerve whereas the other otators pass anterior (see figure 2).Ħ. The primary difference between the PM and other short rotators is the relationship to the SN. PM is closely associated with the other short hip rotators that lie inferior such as the superior gemellus, obturator internus, inferior gemellus and obturator externus(2). Due to its large volume in the greater sciatic foramen, it has the potential to compress the numerous vessels and nerves that exit the pelvis. The nerves and blood vessels in the suprapiriform foramen are the superior gluteal nerve and vessels, and in the infra- piriforma fossa are the inferior gluteal nerves and vessels and the sciatic nerve (SN)(5). As it courses antero-laterally through the greater sciatic foramen, it tapers out to form a tendon that is attached to the superior-medial surface of the greater trochanter, commonly blending with the common tendon of the obturator internus and gemelli muscles(6). PM is a thick and bulky muscle, and as it passes out of the pelvis through the greater sciatic foramen, it divides the foramen into the suprapiriform and infra-piriform foramina(5). Occasionally its origin may be so broad that it joins the capsule of the sacroiliac joint above and with the sacrotuberous and/or sacrospinous ligament below(3,4). The PM originates on the anterior surface of the sacrum and is anchored to it by three fleshy attachments between the first, second, third and fourth anterior sacral foramina(2).
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Its name is derived from the Latin word ‘pirum’ meaning ‘pear’ and ‘forma’ meaning ‘shape’ – ie a pear shaped muscle (see Figure 1)(1). The name piriformis was first coined by Belgian Anatomist Adrian Spigelius in the early 17th century. Furthermore, the PM also grabs attention due to its role in the contentious ‘piriformis syndrome’, a condition implicated as a potential source of pain and dysfunction, not only in the general population but in athletes as well. It is a muscle that has a role in controlling hip joint rotation and abduction, and it is also a muscle made famous due to its ‘inversion of action’ in rotation. The piriformis muscle (PM) is well-known in the fraternity of sports medicine as a significant muscle in the posterior hip.