Contents

Name of bone

Coccyx

Location/Articulation

Final segment of the human vertebral column. Comprising three to five separate or fused vertebrae (the coccygeal vertebrae) below the sacrum, the coccyx is attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.

Muscle and ligament attachments

In humans and other tailless primates (eg great apes) since Nakalipithecus (a Miocine hominoid), the coccyx is the remnant of a vestigial tail, but still not entirely useless; it is an important attachment for various muscles, tendons and ligaments  — which makes it necessary for physicians and patients to pay special attention to these attachments when considering surgical removal of the coccyx. Additionally, it is also part of the weight-bearing tripod structure which act as a support for a sitting person. When a person sits leaning forward, the ischial tuberosities and inferior rami of the ischium take most of the weight, but as the sitting person leans backward, more weight is transferred to the coccyx.

The anterior side of the coccyx serves for the attachment of a group of muscles important for many functions of the pelvic floor (ie, defecation, continence): the levator ani muscle, which include coccygeus, iliococcygeus, and pubococcygeus. Through the anococcygeal raphe, the coccyx supports the position of the anus. Attached to the posterior side is the gluteus maximus which extends the thigh during ambulation

Many important ligaments attach to the coccyx:

  • The anteriorand posterior sacrococcygeal ligaments are the continuations of the anterior and posterior longitudinal ligaments that stretch along the entire spine.
  • The lateral sacrococcygeal ligaments complete the foramina for the last sacral nerve
  • Some fibers of the sacrospinousand sacrotuberous ligaments (arising from the spine of the ischium and the ischial tuberosity respectively) also attach to the coccyx.

Surface anatomy

The coccyx is usually formed of four rudimentary vertebrae (sometimes five or three). It articulates superiorly with the sacrum. A rudimentary body and articular and transverse processes may be traced in each of the first three segments; the last piece (sometimes the third) is a mere nodule of bone. The transverse processes is most prominent and noticeable on the first coccygeal segment. All the segments are destitute of pedicleslaminae and spinous processes. The first is the largest; it resembles the lowest sacral vertebrae, and often exists as a separate piece; the last three diminish in size from above downward.

Most anatomy books wrongly state that the coccyx is normally fused in adults. In fact, it has been shown that the coccyx may consist of up to five separate bony segments, the most common configuration being two or three segments. Only about 5% of the population have a coccyx in one piece, separate from the sacrum, as described in anatomy books.

Surfaces
  • The anteriorsurface is slightly concave and marked with three transverse grooves that indicate the junctions of the different segments. It gives attachment to the anterior sacrococcygeal ligament and the Levatores ani and supports part of the rectum
  • The osteriorsurface is convex, marked by transverse grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. Of these, the superior pair are large, and are called the coccygeal cornua; they project upward, and articulate with the cornua of the sacrum, and on either side complete the foramen for the transmission of the posterior division of the fifth sacral nerve
  • The lateral borders are thin and exhibit a series of small eminences, which represent the transverse processes of the coccygeal vertebrae. Of these, the first is the largest; it is flattened from before backward, and often ascends to join the lower part of the thin lateral edge of the sacrum, thus completing the foramen for the transmission of the anterior division of the fifth sacral nerve; the others diminish in size from above downward, and are often wanting. The borders of the coccyx are narrow, and give attachment on either side to the sacrotuberous and sacrospinous ligaments, to the coccygeus in front of the ligaments, and to the gluteus maximus behind them.
Apex
  • The apex is rounded, and has attached to it the tendon of the Sphincter ani externus. It may be bifid.
Sacrococcygeal and intercoccygeal joints
  • The joints are variable and may be:
    • Synovial joints
    • Thin discs of fibrocartilage
    • Intermediate between these two
    • Ossified

Radiography

Enter radiographic images and landmarks

Physical examination

Enter relevant physical exam maneuvers for this bone

Embryology

Enter embryology for this bone

Anomalies

Enter anomalies for this bone

Injuries/Disorders

Injuring the coccyx can give rise to a condition called coccydynia. A number of tumors are known to involve the coccyx; of these, the most common is sacrococcygeal teratoma. Both coccydynia and coccygeal tumors may require surgical removal of the coccyx (coccygectomy) One complication of cocygectomy is a coccygeal hernia. Fortunately, most cases of coccyx pain respond well to nonsurgical treatment, such as medications given by local injection (often done under fluoroscopic guidance).

Figures


Figure 1. Anterior and posterior views of the coccyx

Attachments:


coccyx.png (image/x-png)