Ultrasound-guided injection technique for coccydynia is utilized in the evaluation and treatment of coccydynia. Coccydynia is a common pain syndrome that is characterized by pain localized to the tailbone that radiates into the lower sacrum and perineum. Affecting females more frequently than males, coccydynia most often occurs after direct trauma to the coccyx from a kick or a fall directly onto the coccyx. Coccydynia also can occur in the parturient after a difficult vaginal delivery. The pain of coccydynia is thought to be the result of strain of the sacrococcygeal ligament or occasionally from occult fracture of the coccyx. Less commonly, arthritis of the sacrococcygeal joint can result in coccydynia.

On physical examination, the patient suffering from coccydynia will exhibit point tenderness over the coccyx with the pain being increased with flexion and extension of the coccyx. Any movement of the coccyx also may cause sharp paresthesias into the rectum, which can be quite distressing to the patient. On rectal examination, the levator ani, piriformis, and coccygeus muscles may feel indurated, and palpation of these muscles may induce severe spasm. Sitting may exacerbate the pain of coccydynia, and the patient may attempt to sit on one buttock to avoid pressure on the coccyx.

Plain radiographs are indicated in all patients who present with pain thought to be emanating from the coccyx to rule out fracture, occult bony pathology, and tumor (Fig. 131.1). Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, prostatespecific antigen, sedimentation rate, and antinuclear antibody. Magnetic resonance imaging (MRI) of the pelvis is indicated if occult mass or tumor is suspected (Fig. 131.2). Radionuclide bone scanning may be useful to rule out stress fractures not seen on plain radiographs. The injection technique presented later serves as both a diagnostic and a therapeutic maneuver.

The five sacral vertebrae are fused together to form the triangular-shaped sacrum (Fig. 131.3). The dorsally convex sacrum inserts in a wedge-like manner between the two iliac bones with superior articulations with the fifth lumbar vertebra and caudad articulations with the coccyx. On the anterior concave surface, there are four pairs of unsealed anterior sacral foramina that allow passage of the anterior rami of the upper four sacral nerves. The posterior sacral foramina are smaller than their anterior counterparts. Leakage of drugs injected into the sacral canal is effectively prevented by the sacrospinal and multifidus muscles. The vestigial bony remnants that are the result of the incomplete fusion of the inferior articular processes of the lower half of the S4 and all of the S5 vertebrae project downward

on each side of the sacral hiatus (see Fig. 131.3). These bony projections are called the sacral cornua and represent important clinical landmarks when performing ultrasound-guided injection for coccydynia. The U-shaped sacral hiatus is covered posteriorly by the sacrococcygeal ligament, which is also an important clinical landmark when performing ultrasoundguided injection for coccydynia (Fig. 131.4). Penetration of the sacrococcygeal ligament provides direct access to the epidural space of the sacral canal. The triangular coccyx is made up of three to five rudimental vertebrae. Its superior surface articulates with the inferior articular surface of the sacrum.