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The sacrum is the keystone of the pelvis; Discuss.

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Introduction

The sacrum is the keystone of the pelvis; Discuss. The pelvis provides a strong and stable connection between the trunk and lower extremities. It consists of four bones: the two hip bones (forming the lateral and anterior walls), and the sacrum and the coccyx (which are part of the vertebral column and form the back wall). The two hip bones articulate anteriorly through the pubic symphysis and posteriorly with the sacroiliac joints forming a strong basin-shaped structure that contains and protects the lower parts of the intestinal and urinary tracts and the internal organs of reproduction. The sacrum is the strongest bone of the pelvis and consists of 5 vertebrae fused together to form a single wedge-shaped bone, which has forward concavity. The upper border articulates with the fifth lumbar vertebrae. Obstetricians count the fifth lumbar as a part of the pelvis, since it is bound to the innominates by ilio-lumbar ligaments, which extend from the tips of its transverse processes to the crests of the ilia. These ilio-lumbar ligaments tend to compel the fifth lumbar vertebra to act somewhat as though it were a portion of the solid pelvis. ...read more.

Middle

All these supply muscles of the pelvis and also those in the lower limb and therefore infer great clinical importance upon the sacrum. Injuries to the sacral plexus are uncommon but may arise due to compression following pelvic tumours causing pain in the lower limb and especially during child birth as the head of the fetus may compress the plexus giving aching pains in the lower limb. There are numerous blood vessels and supplies that pass through and around the sacrum that give it heightened importance in the pelvis. The lateral sacral arteries pass medially and descend anterior to the sacral ventral rami, giving off spinal branches that pass through the pelvic sacral foramina and supply the spinal meninges and the roots of the sacral nerves. Some branches of the lateral sacral arteries pass from the sacral canal through the dorsal foramina to supply the muscles and skin overlying the sacrum. The median sacral artery is a small unpaired artery that arises from the posterior surface of the abdominal aorta, just superior to its bifurcation and runs anterior to the body of the sacrum to end in a series of anastomoses that form the coccygeal body. ...read more.

Conclusion

The sacrum articulates by its auricular surfaces with those of the ilia. The articulating surfaces of both bones are covered with cartilage. The joints are surrounded by capsular ligaments and contain synovial sacs. The opposing auricular surfaces are reciprocally, slightly, uneven but not enough so to sustain any weight without ligaments. The structure of the sacro-iliac synchondroses indicates that movement is possible and, in fact, probable. The primary object of the movement is to produce elasticity in the pelvic girdle and interrupt shocks which would be transmitted from the legs to the trunk. In conclusion, we can see how the sacrum positively contributes to pelvis by being the strongest bone, providing a comprehensive nerve supply, having important articulations with the pelvis, being the site of muscle attachments of the pelvic floor, providing shape to the pelvis by means of the sacral curve and it's association with the blood vessels in the area. However, despite all these essential roles, the sacrum is not mobile and it doesn't offer any support when either sitting or standing. In light of all that has been said about the sacrum, I think that it plays an important role in the pelvis and can be considered it's keystone. Jubin Joseph ...read more.

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