Download BONY PELVIS

BONY PELVIS: SACRUM and JOINTS OF PELVIS S-IV RM02
Learning Objectives.
At the end of lecture students should be able to know,
What is bony pelvis,
Surfaces of sacrum.
Articulation.
Muscles associated with sacrum.
Differences between male and female sacrum.
Describe the types of pelvic joints.
Discuss the articulation and functions of the joints.
The bony pelvis provides a strong, stable connection between the trunk and the lower extremities.
The bony pelvis is composed of four bones:
the two hip bones, which form the lateral and anterior walls, and
a sacrum and a coccyx, which are part of the vertebral column and form the back wall.
The pelvis is divided into two parts by the pelvic brim.
Above the brim is the false pelvis, which forms part of the abdominal cavity.
Below the brim is the true pelvis.
The pelvic brim is formed by:
The sacral promontory (anterior and upper margin of the first sacral vertebra) behind,
The ileopectineal lines (a line that runs downward and forward around the inner surface of the ileum)
laterally, and
The symphysis pubis (joint between bodies of pubic bones) anteriorly.
Sacrum
The sacrum consists of five rudimentary vertebrae fused together to form a single wedge-shaped bone
with a forward concavity—articulate with hip bone—sacroiliac joint.
The upper border or base of the bone articulates with the fifth lumbar vertebra.
The narrow inferior border articulates with the coccyx.
Bony Feature
Triangular bone has:
Base –upper end.
Apex –lower end.
Four surfaces—pelvic, dorsal and right and left lateral surfaces.
Base Of Sacrum
The base of the sacrum, which is broad and expanded, is directed upward and forward.
In the middle is a large oval articular surface, the upper surface of the body of the first sacral vertebra,
which is connected with the under surface of the body of the last lumbar vertebra by an intervertebral
fibrocartilage.
Behind this is the large triangular orifice of the sacral canal, which is completed by the laminæ and
spinous process of the first sacral vertebra.
Apex
The apex is directed downward, and presents an oval facet for articulation with the coccyx.
The pelvic surface of the sacrum is concave from above downward.
The dorsal surface of the sacrum is convex and narrower than the pelvic.
The lateral surface of the sacrum is broad above, but narrowed into a thin edge below.
The base of the sacrum, which is broad and expanded, is directed upward and forward.
The apex is directed downward, and presents an oval facet for articulation with the coccyx.
The pelvic surface is concave from above downward.
Its middle part is crossed by four transverse ridges, the positions of which correspond with the
original planes of separation between the five segments of the bone.
The body of the first segment is of large size, and in form resembles that of a lumbar vertebra; the
succeeding ones diminish from above downward, are flattened from before backward.
At the ends of the ridges are seen the anterior sacral foramina four in number on either side Sacral
canal thru intervertebral foramina.
The vertebral foramina together form the sacral canal.
The laminae of the fifth sacral vertebra, and sometimes those of the fourth, fail to meet in the midline,
forming the sacral hiatus.
Dorsal Surface
The dorsal surface is convex and narrower than the pelvic surface.
In the median plane it displays a crest, the medial sacral crest, bears by three or four tubercles, the
rudimentary spinous processes of the upper three or four sacral vertebrae.
Below the 4th tubercle– U-shaped gap in the posterior wall of scaral canal—called sacral hiatus.
Lateral to the median crest –posterior surface is formed by the fused laminae.
On either side of the middle sacral crest is a shallow groove, the sacral groove, which gives origin to the
Multifidus.
On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the
articular processes which together form the indistinct sacral articular crests.
Lateral to the articular processes are the four posterior sacral foramina.
They are smaller in size and less regular in form than the anterior, and transmit the posterior divisions
of the sacral nerves.
On the lateral side of the posterior sacral foramina is a series of tubercles, which represent the
transverse processes of the sacral vertebrae, and form the lateral crests of the sacrum.
Lateral Surface
The lateral surface is broad above, but narrowed into a thin edge below.
The upper half presents in front an ear-shaped surface, the auricular surface, covered with cartilage in
the fresh state, for articulation with the ilium.
The thin lower half of the lateral surface gives attachment to the sacrotuberous and sacrospinous
ligaments, to some fibers of the Glutæus maximus behind, and to the Coccygeus in front.
Laterally, the sacrum articulates with the two iliac bones to form the sacroiliac joints.
The anterior and posterior surfaces of the sacrum possess on each side four foramina for the passage
upper four sacral nerves.
Articulations.
Sacrum articulates with four bones:
The last lumbar vertebra above
The coccyx (tailbone) below
The illium portion of the hip bone on either side
It is called the sacrum when referred to all of the parts combined, but sacral vertebrae when referred
individually.
Attachments on the sacrum
Anterior and posterior edges of the body of the first sacral vertebra gives attahment –lowest fibers of
the anterior and posterior longitudinal ligamnet.
The rough part of the ala gives attachment to the iliacus anteriorly and also provides attachment to the
lumbosacral ligament posteriorly. Upper part of sacroiliac ligament is attached to its margin.
Pelvic surface—lateral to the bodies of the middle three pieces—attachment of piriformis E –shapesd
attachment.
The dorsal surface gives origin of the erector spinae along a U-shaped lined passing over the spinous and
transverse tubercles—multifidus.
Interosseus sacroilic ligament—auricular surface.
Inferior lateral angle gives attachment to the lateral sacrococcygeal ligament.
The sacrum is usually wider in proportion to its length in the female than in the male.
Pelvic Joints
lumbosacral joint.
Sacrococcygeal and intercoccygeal joint.
Sacroiliac joint.
Pubic symphysis.
Lumbosacral joint
The joint b/w the 5th lumber vertebra and base of the sacrum—similar typical intervertebral joint.
Disc is thick – thickest anteriorly.
Stability:
Wide articular space.
Iliolumber ligament.
Body of the 5th lumber –120 degree angle with sacrum.
The sacrum is tilted forward so that it forms an angle with the fifth lumbar vertebra, called the
lumbosacral angle.
Clinical application
Sacralization.
Lumbralization.
Spina bifida.
Spondylolisthesis.