Sacrococcygeal joint

Articular surfaces

The articular surfaces that comprise the sacrococcygeal joint are the apex of sacrum and the base of coccyx. Both of them are lined by a layer of hyaline cartilage. The surfaces are united by an ellipsoid fibrocartilaginous articular disc. The joint may become partially or completely obliterated later in life.

Ligaments and joint capsule

The sacrococcygeal joint doesn’t have an articular capsule. It is surrounded and stabilized by 5 ligaments;

• The anterior sacrococcygeal ligament, which extends from the anterior surface of the sacrum to the anterior surface of the apex of coccyx.
• The superficial posterior sacrococcygeal ligament, that arises from the margin of the sacral hiatus and attaches to the dorsal surface of the coccyx.
• The deep posterior sacrococcygeal ligament, which spans from the dorsal surface of the fifth sacral segment to the dorsal surface of coccyx.
• The lateral sacrococcygeal ligament, that attaches to the inferolateral angle of the sacrum and the transverse processes of the coccyx.
• The intercornual ligament, a band that connects the cornua of the sacrum and coccyx.

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Innervation

The sacrococcygeal joint is innervated from the sacral spinal nerves S4-S5 and the coccygeal spinal nerve Co.

Blood supply

The blood supply to the sacrococcygeal joint comes from the inferior lateral sacral and median sacral arteries. The former is a branch of the internal iliac artery, while the latter arises from the terminal bifurcation of the abdominal aorta.

Movements

Since the sacrococcygeal joint is a symphysis, it is only slightly mobile. The movements within it are entirely passive, limited to a small degree of passive flexion and extension. There are no muscles acting directly upon the joint. Instead, these movements happen when the intra-abdominal pressure is increased, which is during labor and defecation.