Human Anatomy - H. I. Koliadenko 2009

Musculoskeletal System
Skeleton of the Lower Limb
Structure and Articulation of Bones

The Pelvic Girdle, or pelvis, consists of two hip bones (ossa coxae), also known as the innominate bones (ossa innominata), and the sacrum (os sacrum). The hip bones are connected anteriorly by a amphiarthrosis joint known as the Pubic Symphysis.

The hip bone (Fig. 37) is composed of three parts: the ilium, the ischium, and the pubis. In individuals up to 15–16 years of age, these three bones are united by Cartilage (synchondrosis). Following this period, the cartilage within the acetabulum ossifies, and the bodies of the three bones fuse to form a single, monolithic hip bone.

The ilium (os ilium) forms the superior part of the hip bone and consists of a body—which contributes to the upper portion of the acetabulum—and a wing, or ala, whose superior margin forms the iliac crest. Anteriorly, the crest terminates in the anterior superior and anterior inferior iliac spines, while posteriorly it forms the posterior superior and posterior inferior iliac spines. Inferior to the posterior inferior spine lies the greater sciatic notch. The internal surface of the ala is concave and referred to as the iliac fossa, inferior to which runs the arcuate line. On the external surface of the ala, there is an auricular surface that articulates with the corresponding surface of the sacrum. Externally, the ala also features three gluteal lines (posterior, anterior, and inferior) for the attachment of the gluteal Muscles.

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Fig. 37. Right hip bone, or os coxae:

1 — ala of ilium; 2 — iliac crest; 3 — anterior superior iliac spine; 4 — anterior inferior iliac spine; 5 — superior ramus of pubis; 6 — pubic crest; 7 — pubis; 8 — inferior ramus of pubis; 9 — inferior ramus of ischium; 10 — ischium; 11 — ischial tuberosity; 12 — superior ramus of ischium; 13 — lesser sciatic notch; 14 — body of ischium; 15 — ischial spine; 16 — acetabulum; 17 — body of ilium; 18 — greater sciatic notch; 19 — posterior inferior iliac spine; 20 — posterior superior iliac spine; 21 — ilium

The ischium (os ischii) forms the inferior part of the hip bone and comprises a body and two rami. Its body forms the posterior portion of the acetabulum. Extending from the body is the superior ramus, which transitions into the inferior ramus. Together, they form the ischial tuberosity, superior to which is the ischial spine. The greater sciatic notch is located superior to the spine, and the lesser sciatic notch is located inferior to it.

The pubis (os pubis) is situated in the anterior part of the hip bone. It consists of a body—which forms the anterior part of the acetabulum—and two rami: a superior and an inferior ramus. Running along the superior ramus is the pubic crest, which terminates in the pubic tubercle. The superior and inferior rami meet to form an angle, the external surface of which is somewhat elongated and rough. Via these surfaces, the two pubic bones articulate through fibrocartilage to form the pubic symphysis, closing the pelvis anteriorly. The rami of the pubic bone, uniting with the rami of the ischium, form the obturator foramen. Once fused, the bodies of the three pelvic bones form the deep acetabulum, the articular surface that articulates with the HEAD of the Femur.

The human pelvis (pelvis) is formed by the two hip bones, the sacrum, and the coccyx. It is divided into the greater (false) pelvis and the lesser (true) pelvis. These regions are separated laterally by the arcuate line of the ilium, posteriorly by the sacral promontory, and anteriorly by the pubic crest and the superior margin of the pubic symphysis. The symphysis is a fibrocartilaginous synchondrosis containing a narrow cleft, which is significantly wider in females than in males. During Pregnancy, the symphyseal cartilage softens, causing the cleft to widen slightly during childbirth to facilitate the passage of the fetus through the pelvic cavity.

Sexual Dimorphism of the pelvis is clearly evident in the subpubic angle: it is acute in males (approximately 70–75°) and obtuse in females (90–100°). This angle forms the pubic arch. The iliac wings are broader and more horizontally oriented in females, whereas in males they are nearly vertical. The anteroposterior and transverse dimensions of the greater pelvis also differ between sexes, averaging 3–4 cm larger in females than in males. The pelvic canal is cylindrical in females and funnel-shaped (conical) in males.

The pelvic bones are connected anteriorly by a slightly movable joint, the pubic symphysis, and laterally by a rigid amphiarthrosis between the auricular surfaces of the ilium and the sacrum (the sacroiliac joint).

The sacroiliac joints are reinforced by short, strong ligaments, complemented by two long ligaments. Both ligaments originate in a fan-like manner: the first from the sacrum and coccyx, and the second from the sacrum alone. The first inserts into the ischial tuberosity, and the second into the ischial spine. Posteriorly, the iliac crest is connected to the transverse processes of the fifth lumbar vertebra by the strong iliolumbar ligament. The sacrum and coccyx are united by a synchondrosis that typically does not ossify until advanced old age. The obturator foramen is closed by the obturator membrane (Fig. 38).

Fig. 38. Ligaments and JOINTS OF THE pelvis (right lateral view):

1 — intervertebral foramen; 2 — interspinous ligament; 3 — supraspinous ligament; 4 — sacral canal; 5 — sacrospinous ligament; 6 — sacrotuberous ligament; 7 — greater sciatic foramen; 8 — lesser sciatic foramen; 9 — obturator membrane; 10 — section of the pubic symphysis; 11 — sacroiliac joint; 12 — sacral promontory; 13 — intervertebral discs; 14 — ligamentum flavum