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5. lay-out phd DEFINITIEF_digitaal2

Chapter 6 (2a) The gluteus medius muscle is a broad, thick, fan-shaped muscle. It originates from the outer surface of the ilium caudal to the iliac crest and inserts at the lateral surface of the greater trochanter. Optionally a deep slip of muscle may be attached to the cranial end of it. The caudal part of the gluteus medius muscle is covered by the gluteus maximus, divided from it by a thin connective tissue septum, and bordered (and sometimes partly covered) by the piriformis muscle. The cranial part of the gluteus medius is covered by a strong deep gluteal fascia, on which the gluteus maximus muscle fibers attach caudally and the gluteus medius muscle fibers attach from the inner side. The craniomedial origin of the gluteus maximus doesn’t reach the midline and is quite thin. More to the lateral side the muscle becomes thicker. Therefore its easier to find an intermuscular septum between the gluteus maximus and medius muscles at a distance of about 7 cm from the midline. The gluteus medius is a strong abductor at the hip joint and important in stabilizing the pelvis: it is largely responsible for pelvic tilt during walking. The caudal part of the muscle, inserting more to the anterior of the greater trochanter, also medially rotates the thigh. (2b) The gluteus minimus muscle is the smallest and thinnest of the gluteus muscles. Like the gluteus medius it is a fan-shaped, triangular muscle. It originates from the outer surface of the ilium, between the middle (anterior) and lower (inferior) gluteal lines and, behind, from the margin of the greater sciatic notch. The muscle fibers converge to an aponeurosis that is continuous with the cranial part of the triangular iliofemoral ligament. This aponeurosis finally, as a capsular expansion, inserts to the anterior surface of the greater trochanter. During locomotion the gluteus minimus exerts the same action as the gluteus medius. The anterior fibers medially rotate the thigh more strongly than the gluteus medius muscle. The muscles described below (2c-e) are all located caudally and deeper than the region of surgical dissection of the sc-GAP (see also ’Arterial topo- graphy’) and are described to complete the muscular anatomy of the gluteal region. (2c). Yet, the piriformis muscle is an important key-structure in the gluteal region to understanding innervation and vascularization (see below). This pear-shaped muscle arises from the internal (anterior) surface of the sacrum, leaving the lesser pelvis through the greater sciatic foramen. It also originates from the region near the posterior inferior iliac spine (PIIS), the adjacent sacroiliac joint capsule and sometimes the inner (pelvic) part of the sacrotuberous ligament. Its insertion, often blended with that of the triceps coxae muscles, which are attaching more posteriorly and caudally, is on the 87


5. lay-out phd DEFINITIEF_digitaal2
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