Sacrococcygeal Joint Injection

Indications and Clinical Considerations

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

On physical examination, the patient exhibits point tenderness over the coccyx with the pain increased with movement of the coccyx. 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 1 buttock to avoid pressure on the coccyx.

Plain radiographs are indicated for all patients with pain thought to be emanating from the coccyx to rule out fracture, occult bony disease, and tumor ( Fig. 146.1 ). On the basis of the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, prostate-specific antigen, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging and ultrasound imaging of the pelvis are indicated if occult mass or tumor is suspected ( Fig. 146.2 ). 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.

Clinically Relevant Anatomy

The triangular sacrum consists of the 5 fused sacral vertebrae that are dorsally convex. The sacrum inserts in a wedgelike manner between the 2 iliac bones, articulating superiorly with the fifth lumbar vertebra and caudally with the coccyx ( Fig. 146.3 ). On the anterior concave surface there are 4 pairs of unsealed anterior sacral foramina that allow passage of the anterior rami of the upper 4 sacral nerves. The posterior sacral foramina are smaller than their anterior counterparts. The vestigial remnants of the inferior articular processes project downward on each side of the sacral hiatus. These bony projections are called the sacral cornua and are important clinical landmarks for performing a caudal epidural nerve block.

The triangular coccyx is made up of 3 to 5 rudimental vertebrae. Its superior surface articulates with the inferior articular surface of the sacrum. The sacral hiatus is formed by the incomplete midline fusion of the posterior elements of the lower portion of the S4 and the entire S5 vertebrae. This U-shaped space is covered posteriorly by the sacrococcygeal ligament, which connects the sacrum to the coccyx.