Together, the ischium and the ramus form the ischial tuberosity. The ischiumįorms the posterior two-fifths of the acetabulum. The ischium is composed of a body, which contributes to the acetabulum, and a ramus. Pelvic Bones – Internal View Ischium Bone: The second column runs from the dome of the acetabulum to the SI joint and allows for force transfer during standing.The first column runs from the ischial tuberosity to the SI joint and allows for force transfer during sitting.The bone in the ilium has two columns, which are extremely thick and strong: See Also: Anterior Approach to the Iliac Crest PSIS: 4 to 5 cm lateral to S2 spinous process important landmark for posterior iliac crest bone graft harvest. Iliac crest: under-skin palpable rim of ilium, it’s an important site for bone graft harvest (iliac tubercle 5 cm posterior to ASIS).ĪSIS: palpable at lateral edge of inguinal ligament origin of sartorius muscle and transverse and internal abdominal muscles.ĪIIS: less prominent origin of direct head of the rectus femoris and iliofemoral ligament (Y ligament of Bigelow) The anterior surface of the ilium forms a fossa and serves as the proximal attachment of the iliacus muscle. The wing serves as the insertion for the gluteus minimus, medius, and maximus. The wing of the ilium spans superiorly from the posterior superior iliac spine (PSIS) to the anterior superior iliac spine The body of the ilium forms the superior two-fifths of the acetabulum. It is composed of a large fan-like wing (ala) and an inferiorly positioned body. The ilium is the largest of these three bones. Pelvic Anatomy – Lateral View Ilium Bone: Pelvic anatomy is composed of two innominate (coxal) bones that articulate with the sacrum and proximal femora.Įach innominate bone is composed of three united bones: ilium, ischium, and pubis, meeting in the acetabular fossa at the triradiate fusion center. Learning Pelvic Anatomy is composed of learning bones, muscles, ligaments, nerves and vascular supply. In 85% of specimens, 1 to 3 branches from S3 and/or S4 nerves pierced or coursed ventral to the sacrotuberous ligament and perforated the inferior portion of the gluteus maximus muscle.A full understanding of pelvic anatomy is required to treat pelvic fractures, to prevent iatrogenic injuries, and to provide the best results. At its midpoint, the sacrospinous ligament median thickness was 5 mm (range, 2–7 mm), and its median height was 14 mm (range, 3–22 mm). The inferior gluteal nerve arose from dorsal surface of combined lumbosacral trunk and S1 nerves in all specimens a contribution from S2 was noted in 46% of hemipelvises. Median closest distance from inferior gluteal nerve to ischial spine and to the midpoint of sacrospinous ligament was 28.5 mm (range, 6–53 mm) and 31.5 mm (range, 10–47 mm), respectively. From a gluteal perspective, the closest structure to ischial spine was the pudendal nerve (median distance, 0 mm range, 0–9 mm). Branches from S3 and/or S4 perforated the ventral surface of coccygeus muscles in 94% specimens. From a pelvic perspective, the closest structure to the superior border of sacrospinous ligament at its midpoint was the S3 nerve (median distance, 3 mm range, 0–11 mm).
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