coccyx

The coccyx, commonly known as the tailbone, is the small, triangular bone at the distal end of the vertebral column. It typically consists of three to five rudimentary vertebrae that are fused in adulthood, most often four. The coccyx articulates superiorly with the sacrum at the sacrococcygeal joint and lies within the pelvic region, where its anterior surface is related to pelvic viscera and its posterior surface bears the remnants of spinal processes.

Anatomically, the coccyx is stabilized by ligaments, including the anterior and posterior sacrococcygeal ligaments and various soft tissue attachments. It serves as an anchor for several muscles and ligaments of the pelvic floor, notably parts of the levator ani and the coccygeus, and it provides attachment to the anococcygeal raphe. Its position and attachments help support pelvic organs and contribute to the structural integrity of the pelvis.

Functionally, the coccyx bears little weight during ordinary upright posture but provides a point of attachment for muscles and ligaments that support the pelvic floor. It can play a minor role in balance when seated and in dispersing pressure on the pelvic region.

Clinical relevance centers on coccydynia, or tailbone pain, which can follow trauma, prolonged sitting, childbirth, or nonspecific causes. Management is typically conservative, including cushions, nonsteroidal anti-inflammatory drugs, physical therapy, and manual techniques; injections or, rarely, coccygectomy may be considered for persistent symptoms.

Developmentally, the coccyx forms from coccygeal vertebrae and may fuse with age. Variations can include differences in the number of segments or atypical fusion. The coccyx is a vestigial structure in humans, representing remnants of a tailed ancestor. Imaging (lateral radiographs, and sometimes CT or MRI) aids evaluation in painful or unclear cases.