The sacrococcygeal

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together ...

(sacrococcygeal articulation, articulation of the sacrum and coccyx) is an amphiarthrodial joint, formed between the oval surface at the apex of the

sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

, and the base of the

coccyx The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...

. It is a slightly moveable jointMorris (2005), p 59 which is frequently, partially or completely, obliterated in old age,Palastanga (2006), p 334 homologous with the joints between the bodies of the

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

Disc

The sacrococcygeal disc or interosseus ligamentHuijbregts (2001), p 13 is similar to the

intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold t ...

s but thinner, thicker in front and behind than at the sides, and with a firmer texture. The articular surfaces are elliptical with longer transversal axes. The surface on the sacrum is convex and that on the coccyx concave. Occasionally the coccyx is freely movable on the sacrum, most notably during

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

; in such cases a

synovial membrane The synovial membrane (also known as the synovial stratum, synovium or stratum synoviale) is a specialized connective tissue that lines the inner surface of capsules of synovial joints and tendon sheath. It makes direct contact with the fibrous ...

is present.

Ligaments

The joint is strengthened by a series of ligaments: * The ventral or

anterior sacrococcygeal ligament The anterior sacrococcygeal ligament or ventral sacrococcygeal ligament consists of a few irregular fibers, which descend from the anterior surface of the sacrum to the front of the coccyx, blending with the periosteum.Morris (2005), p 59 This sh ...

is an extension of the

anterior longitudinal ligament The anterior longitudinal ligament is a ligament that runs down the anterior surface of the spine. It traverses all of the vertebral bodies and intervertebral discs on their ventral side. It may be partially cut to treat certain abnormal curvatur ...

(ALL) that runs down along the spine on the anterior sides of the bodies of the vertebrae. It consists of a few irregular fibers that attach to the anterior sides of the sacrum and coccyx and blend with the

periosteum The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. Endosteum lines the inner surface of the medullary cavity of all long bones. Structure ...

. * The dorsal or

posterior sacrococcygeal ligament The posterior sacrococcygeal ligament or dorsal sacrococcygeal ligamentOMD: Definition is a ligament which stretches from the sacrum to the coccyx and thus dorsally across the sacrococcygeal symphysis shared by these two bones. This ligament is di ...

has a deep and a superficial part: ** The deep dorsal ligament is a flat band which corresponds to the

posterior longitudinal ligament The posterior longitudinal ligament is a ligament connecting the posterior surfaces of the vertebral bodies of all of the vertebrae. It weakly prevents hyperflexion of the vertebral column. It also prevents posterior spinal disc herniation, althou ...

(PLL) that run down inside the

vertebral canal The spinal canal (or vertebral canal or spinal cavity) is the canal that contains the spinal cord within the vertebral column. The spinal canal is formed by the vertebrae through which the spinal cord passes. It is a process of the dorsal body ca ...

on the posterior surfaces of the bodies of the vertebrae. From the posterior side of the fifth sacral body inside the sacral canal, the dorsal ligament stretches to the posterior side of the coccyx, to attach deep to the superficial dorsal ligament. ** The superficial dorsal ligament corresponds to the

ligamenta flava The ligamenta flava (singular, ''ligamentum flavum'', Latin for ''yellow ligament'') are a series of ligaments that connect the ventral parts of the lamina of the vertebral arch, laminae of adjacent vertebrae. They help to preserve Bipedalism, upr ...

and closes the posterior aspect of the distal end of the vertebral canal. It stretches from

median sacral crest The sacrum (plural: ''sacra'' or ''sacrums''), in human body, human anatomy, is a large, triangular bone at the base of the vertebral column, spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situ ...

and the free margin of the

sacral hiatus The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

to the dorsal surface of the coccyx. * The

lateral sacrococcygeal ligament In the human body, the lateral sacrococcygeal ligaments is a pair of ligaments stretching from the lower lateral angles of the sacrum to the transverse processes of the first coccygeal vertebra. Together with the anterior, posterior, and inter ...

s run from the lower lateral angles of the sacrum to the

transverse process The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

es of the first coccygeal vertebra to complete the

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

for the last sacral nerve. Three lateral ligaments have been reported on either side. * The interarticular or intercornual sacrococcygeal ligaments stretches from the cornu of the sacrum to the cornu of the coccyx.

Movements

Movements in the joint are restricted to

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

and

extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * E ...

. These essentially passive movements occurs during

defecation Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging f ...

and

labour Labour or labor may refer to: * Childbirth, the delivery of a baby * Labour (human activity), or work ** Manual labour, physical work ** Wage labour, a socioeconomic relationship between a worker and an employer ** Organized labour and the labour ...

. When movements in the sacrum increase the anteroposterior diameter of the

pelvic outlet The lower circumference of the lesser pelvis is very irregular; the space enclosed by it is named the inferior aperture or pelvic outlet. It is an important component of pelvimetry. Boundaries It has the following boundaries: * anteriorly: the pub ...

, movements in the sacrococcygeal joint can further increase this diameter.

Palpation

The joint is

palpable Palpation is the process of using one's hands to check the body, especially while perceiving/diagnosing a disease or illness. Usually performed by a health care practitioner, it is the process of feeling an object in or on the body to determine ...

deep within the natal cleft, and can be felt as a horizontal groove. With the palpating finger on the dorsal surface of the coccyx, a degree of rotation can be produced with an applied forward pressure.

Disc

Ligaments

Movements

Palpation

See also

Notes

References

External links