Trunk (thorax, abdomen, back)

Tailbone

Os coccygis

Origin

Consists of 3 to 5 fused rudimentary vertebrae inferior to the sacrum

Insertion

Attachment site for levator ani, coccygeus, gluteus maximus, and anococcygeal ligament

Function

Provides posterior anchor for pelvic floor muscles and bears partial weight in sitting position

Innervation

Coccygeal nerve and sacral plexus (S4–Co1)

Movement & chain

Slight passive anteroposterior flexion during defecation and childbirth

Palpation

Palpable at the top of intergluteal cleft below the sacral apex

Clinical

Coccydynia (chronic tailbone pain following fall onto buttocks or difficult delivery); coccyx fracture

Segmental innervation

S4–Co1

In clinical practice

Donut cushions and pelvic floor physiotherapy for management of refractory tailbone pain

Region in the model

Trunk (thorax, abdomen, back)