Coccyx Pain Workup

Some physicians may have an unintentional bias against patients with coccydynia, inappropriately attributing the pain to underlying psychological conditions, such as anxiety, neurosis, or even hysteria.^[2] Patients with coccydynia often report frustration with physicians who minimize their symptoms or tell them that the pain is "all in their head."^[4] However, behavioral assessments of patients with coccydynia have shown a psychological profile similar to that of any other group of patients (ie, without any increased evidence of overt psychopathology).^[2]

Patients with coccydynia deserve appropriate workup, treatment, and compassion, the elements of care provided to patients with other neurologic or musculoskeletal chronic pain syndromes.

Electrodiagnostics

Electromyography (EMG) and nerve conduction studies (NCSs) are usually unnecessary in cases of isolated coccydynia. However, electrodiagnostics are potentially helpful in cases in which concomitant lumbosacral radiculopathy is suspected.

Anesthesia response

The patient's response to injection of local anesthetic agents, with or without corticosteroids, can provide helpful information regarding whether the patient's pain generator has been accurately identified. However, the injection response may not be considered truly diagnostic of whether the pain generator is a specific anatomic structure unless the injection is performed with the guidance of fluoroscopy or other imaging aids. Similarly, if large volumes of fluid are injected, extravasation from the targeted site decreases the diagnostic specificity.

Complications from focal injections seem to be uncommon if the injections are performed using a sterile technique and fluoroscopy or other image guidance to assist in accurate placement. Some patients may experience exacerbation during the first few days after the injection procedure, but this is generally only temporary and self-limited.

Histologic findings

A single case series of 8 patients who had undergone coccygectomy (surgical removal of the coccyx) revealed that in 5 patients, the main histologic change was disc degeneration at the sacrococcygeal joint; the surgical outcome was poor in all 5 patients. Two other cases had degenerative articular cartilage changes at the sacrococcygeal joint, and the postsurgical outcome was excellent in 1 of these patients and good in the second one.^[10]

Lab work

No specific blood work is recommended for coccydynia.

Plain radiographs are typically the initial imaging study of choice for patients with coccydynia, especially in cases of focal sacrococcygeal trauma.

Plain radiographs may reveal fractures, abnormal sacrococcygeal curvature, osteophytes, or dislocations of the sacrococcygeal junction or intracoccygeal segments.^{[12, 13]}

However, be aware that there is substantial baseline, preinjury coccygeal variability with regard to the angulation of the coccygeal vertebrae and the sacrococcygeal joint, the degree of fusion between the coccygeal vertebrae and the sacrococcygeal joint, and the total number of coccygeal vertebrae. This preinjury variability creates challenges when interpreting sacrococcygeal imaging studies. It may become difficult to know whether apparent abnormalities truly signal acute or ongoing pathology or just represent normal baseline anatomic variability.

Lateral view

In the lateral view, the easiest way to identify the sacrococcygeal junction typically is to look just anteroinferior to the sacral cornua and anterior to the coccygeal cornua. The cornua are horn-shaped, bony projections; 2 sacral cornua (the right and left cornua) extend inferiorly from the sacrum, and 2 coccygeal cornua extend superiorly from the coccyx. On the lateral radiographic view, the 2 sacral cornua seem to overlap and appear as one, with a similar overlapping noted for the coccygeal cornua.

Some French clinicians advocate radiographically assessing sacrococcygeal mobility through the comparison of lateral radiographs performed while the patient is seated versus standing.^{[12, 13]} Within most radiology departments, however, such dynamic radiography is not widely performed or readily available.

Anteroposterior view

In the anteroposterior (AP) view, the first (most superior) coccygeal vertebra can be distinguished from the other coccygeal vertebrae by the presence of the bilateral coccygeal cornu posteriorly and the bilateral transverse processes laterally. (The transverse processes of the first coccygeal segment are much wider and much more prominent than are the transverse processes of the inferior coccygeal vertebrae.)

The apex of the coccyx is usually rounded, but a bifid appearance can sometimes be appreciated in the AP radiographic view. The apex is typically midline but may deviate laterally.

Coned-down view

In addition to obtaining the standard AP and lateral lumbosacral radiographs, explicitly requesting coned-down (focused) views of the coccyx itself is often important to ensure adequate visualization and an appropriate degree of radiographic exposure (see the image below). Standard sacrococcygeal radiographs include the entire sacrum and coccyx, the lower lumbar region, and, frequently, the bilateral ilia and hip joints. Thus, images that are not coned-down to focus on the coccyx often result in suboptimal radiographic exposure at the coccyx, making the coccygeal segments difficult to clearly visualize.

Lumbosacral magnetic resonance imaging (MRI) studies usually fail to include the coccyx unless a specific request is made for coccygeal visualization. Thus, patients whose imaging studies have been limited to a standard lumbosacral MRI scan (without plain radiographs first and without additional MRI of the coccyx) have often received no radiologic imaging of the coccyx.

Lumbosacral MRI would be most helpful in cases in which the coccygeal pain is suspected to be referred from anatomic structures located more superiorly within the spine (ie, at the lumbar or sacral regions).

Lumbosacral MRI can help to diagnose lumbosacral disc pathology, degenerative joint disease of the lumbosacral facet joints (zygapophyseal joints), and pathology of the sacroiliac joints. However, the notable caveat is that many degenerative changes of these structures are considered to be a normal, often nonsymptomatic, part of the aging process. Thus, any such abnormalities must be put into the context of the patient’s overall history and physical so that the physician can make an educated determination as to whether the lumbosacral MRI findings represent pain generators or incidental findings.

In most cases of coccydynia, bone and computed tomography (CT) scanning are not necessary. In cases of suspected fracture with negative or inconclusive plain radiographic findings, however, these studies can be performed to better delineate the bony anatomy. This is notable because normal coccygeal variability and technical difficulties with radiographic exposure sometimes limit the ability of plain radiographs to aid in the diagnosis of a coccygeal fracture.

Bone and CT scanning studies may particularly be considered in medicolegal cases in which objective evidence is needed regarding the presence or absence of a coccygeal fracture or in cases in which bony cancer or metastases are being considered.

Note that bone scans that only include AP and/or PA views generally fail to show the coccyx, since coccygeal visualization is obstructed by the nuclear medicine materials pooling in the bladder prior to urination. Using oblique and lateral views, rather than just the AP or PA views, can help avoid this problem.

CT scanning and/or MRI of the pelvis can be helpful in cases in which intrapelvic pathology (ovarian, cervical, colon, testicular, or prostate cancer or their associated metastases) is suspected.^[14] CT scanning may be particularly helpful with bony lesions and is less expensive than MRI.

MRI is superior to CT scanning at visualization of soft-tissue structures, including with regard to showing pathology of the ovaries, uterus, prostate, urinary bladder, and bowels. Also, unlike MRI, CT scanning carries notable risks of radiation exposure.