The pelvis (pelvis)

The pelvic girdle is joined to the spinal column (columna vertebralis). Its rigidity and stability give the human body a safe stand and upright posture. Its main task is to transfer the body load from the spinal column to the two thighbones (os femoris).

The pelvic girdle consists of the two hipbones (ossa coxae) and the sacrum (os sacrum) together with the coccyx (os coccygis). Together the hipbones and the sacrum make up the bony pelvis.

The hipbone consists of three parts: these are the ilium (os ilium), ischium (os ischii) and pubis (os pubis). These three bones merge together at around 15 years of age in the area of the acetabulum to form the hipbone.

The sacrum and hipbone are joined on both sides by the sacroiliac joint (articulatio sacroiliaca). But its scope for movement is limited to a great extent by the tight ligaments, which give the pelvis greater stability. The joint is very important for shock absorption for the spinal column. At the front of the pelvic girdle, the two hipbones are joined by a cartilage connection, the pubic symphysis (symphyse).

The pelvis is differentiated into the large and small pelvis. The large pelvis consists of the wings of the ilium on the sides and the sacrum at the back. The small pelvis is composed of the two pubic bones and the two ischias bones.

The female and male pelvis differ. Whereas in the woman the two pelvic wings protrude more and the obturator foramen (foramen obturatum) has an oval shape, the male pelvis is smaller and the obturator foramen rounder. The pelvic outlet in the female pelvis is also wider.
 

The sacrum (os sacrum)

The sacrum originated from the fusion of the 5th sacral vertebra with its intervertebral discs (discus intervertebrales), which are present in the child as primary cartilaginous joints. In adults they can only be detected as transverse lines on the front of the sacrum.

The surface of the sacrum is concave to the front. The side towards the pelvis (pelvis) is referred to as facies pelvina, and the side pointing to the back as facies dorsalis. The surface adjoining the lumbar spinal column is called the basis ossis sacri.

An apex protruding downwards (apex ossis sacri) forms the connection to the adjoining coccyx (os coccygis). The uniformly convex back surface of the sacrum has five bone crests (longitudinal ridges) resulting from the spinal, articular and transverse processes. In the middle is the crista sacralis mediana, resulting from the fusion of the spinal processes (processus spinosi).

The articular processes (processus articulares) have resulted in two irregular ridges, the cristae sacrales intermediae. The original transverse processes (processus transversi) have fused together to become the two somewhat more protruding cristae sacrales laterales.

From the basis of the sacrum there are two articular processes (processus articulares). Inside the sacrum, the vertebral canal (canalis vertebralis) continues as the sacral canal (canalis sacralis).

The surface pointing towards the pelvis contains the transverse lines of the merged vertebrae (lineae transversae), together with the openings (foramina sacralia pelvina) for the passage of the spinal nerves (mervi spinales).

The sacrum in men is somewhat longer and narrower than in women, and also has a somewhat greater curvature.

The hip bone (os coxae)

The hip bone consists of three bones: the ilium (os ilium), the ischium (os ischii) and the pubis (os pubis). In the child these bones are still separated from each other by cartilage growth joints, but in the adult they have fused together to form one uniform bone.

These three bones meet in the so-called acetabulum (acetabulum), which forms the socket of the hip joint. The ilium consists of a body (corpus osssi illi) and a protruding part, the iliac wing (ala ossis ilii), which bears the pelvic organs. On the inside, both parts are separated by a bony ridge, the linea arcuata. On the outside the body, which makes up part of the acetabulum, is limited by a furrow, the sulcus supraacetabularis.

The inner surface of the iliac wing has a flat furrow, the fossa iliaca. The upper edge is called the iliac crest (Crista iliaca). It starts at the front upper iliac spine (spina iliaca anterior superior) and runs to the rear upper iliac spine (spina iliaca posterior superior) and to the rear lower iliac spine, (spina iliaca posterior inferior), which is positioned underneath it.

The front lower iliac spine (spina iliaca anterior inferior) protrudes below the front upper iliac spine. This is the origin for the straight thigh muscle. Towards the sacrum, the ilium has an ear-shaped bent connection surface covered in cartilage for the sacroiliac joint (articulatio sacroiliaca).

At the boundary to the ischium, the iliac has a larger incisure, the incisura ischiadica major. The ischium consists of a body (corpus) and a ramified part (ramus ossis ischii). The ischiac tubercle is located between the two (tuber ischiadicum).

The corpus has the largest share in the acetabulum (acetabulum). Together with the ramus inferior ossis pubis, a section between the ischias and the pubic symphysis, (symphysis), the ramus ossis ischii constitutes the lower limit of the obturatum foramen (foramen obturatum). This is almost entirely covered by a membrane.

The ischium forms the ischiac spine (spina ischiadica), a bony process pointing inwards. This is the attachment point for a ligament leading to the coccyx and sacrum. The ischiac spine also separates the already mentioned large ischiac incisure (Incisura ischiadica major), which consists partly of the ischium and partly of the ilium, and extends to the underside of the facies auricularis from the smaller incisure, the incisura ischiadica minor.

The pubis consists of the corpus ossis pubis and two pubic branches, the ramus superior and the ramus inferior. These two form the boundary to the front and below the obturatem foramen (foramen obturatum). The upper edge of the upper pubic branch is referred to as pubic crest (pecten ossis pubis). It runs into the pubic tubercle (tuberculum pubicum).

The limit between pubis and ilium consists of a bone protrusion, the eminentia iliopubica. Between the two pubic bones is the pubic synphysis (symphysis pubica). This has a cartilage layer, the interpubic disc (discus interpubicus). It is connected to the cartilage layers of the adjacent pubic bones and is limited by ligaments, which at the same time hold the pubic bones.