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Coccyx is generally formed of four and sometimes three or five segments. It joins mainly with Sacrum. All segments are deprived of Pedicles, Laminae and Spinous Processes (unlike a typical vertebrae). The first segment is the largest and resembles with the Lowest Sacral Vertebra. It mostly exists as a separate piece. The last three segments gradually decrease in size from above to downward.
The Anterior or front surface is a little concave and is marked with three transverse grooves that show the joining of different segments. Coccyx gives attachments and support to three different regions i.e.
Anterior Sacrococcygeal Ligament
Levatores Ani (broad, thin muscles at side of Pelvis)
Some part of Rectum
The Posterior or back surface has same transverse grooves like on the anterior surface presenting Row of Tubercles on both sides and jointing process of Coccygeal Vertebrae. Superior pair are generally called Coccygeal Cornua (Horn) that project upward and joint with Cornua of Sacrum and on both side it completes the posterior division of the Fifth Sacral Nerve.
The lateral borders of Coccyx are thin and presents series of small Eminences which exhibit the transverse processes of the Coccygeal Vertebrae. Of these segments, first is the largest, flattened from before its back and often moves upward to join the lower lateral edge of the Sacrum. The other segments decrease in size from above to downward. Coccyx’s borders are narrow and give attachments to various ligaments i.e.
Sacrotuberous Ligaments (Ligament at lower and back part of Pelvis)
Sacrospinous Ligaments (Triangular ligament attached to Ischial Spine)
Coccygeous (muscle of Pelvic floor) in front of the ligaments
Gluteus Maximus (one of the largest Gluteal muscles forming the prominence of Buttocks )
Apex of the Coccyx is round in shape and has a tendon attached to it known as Sphincter Ani Externus.
Coccyx is the remnant of Vestigial tail but still is not completely useless. It is important as it provides attachments to various muscles, ligaments and tendons which makes it necessary for for surgeon and patient to pay attention when deciding the surgical removal of Coccyx. It is also a part of Tripod structure which acts as support for the sitting person. When a sitting person leans backwards most of the weight is transferred to the Coccyx.
Injury of the Coccyx leads to a painful condition named as Coccydynia which may also lead to loss of connection with one or more bones thus resulting in fractured Tailbone. Tumors are also known to be involved with Coccyx. Out of these the most common one is known as Sacrococcygeal Teratoma. Both of these conditions may require surgical removal of Coccyx. The procedure is called Coccygectomy. The complication generally during the Coccygectomy is Coccygeal Hernia.