eMedicine Specialties > Physical Medicine and Rehabilitation > Lower Limb Musculoskeletal Conditions

Coccyx Pain: Differential Diagnoses & Workup

Author: Patrick M Foye, MD, FAAPMR, FAAEM, Associate Professor of Physical Medicine and Rehabilitation, Co-Director of Musculoskeletal Fellowship, Co-Director of Back Pain Clinic, Director of Coccyx Pain (Tailbone Pain, Coccydynia) Service (www.TailboneDoctor.com), University of Medicine and Dentistry of New Jersey, New Jersey Medical School
Coauthor(s): Charles J Buttaci, DO, PT, Pain Management, Northeast Orthopedics; Matthew Kirk Sorensen, EMT-B, Kean University
Contributor Information and Disclosures

Updated: Jan 29, 2009

Differential Diagnoses

Other Problems to Be Considered

Coccygeal fracture
Sacrococcygeal dislocation
Intracoccygeal dislocation (dislocation of one coccygeal segment from another)
Intrapelvic malignancy and/or metastatic lesions
Ischial bursitis
Sacroiliac joint pain
Ovarian cyst
Fibroid uterus
Pilonidal cyst

Workup

Laboratory Studies

• No specific blood work is recommended for coccydynia.

Imaging Studies

• Plain radiographs
  • 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.^6,7
  • However, the existence of 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—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.
  • In addition to obtaining the standard anteroposterior (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 image below and Image 3). 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 there, making the coccyx difficult to clearly visualize.

• 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.
• In the 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.
• Some French clinicians advocate radiographically assessing sacrococcygeal mobility through the comparison of lateral radiographs performed while the patient is seated versus standing.^6,7 Within most radiology departments, however, such dynamic radiography is not widely performed or readily available.
• Lumbosacral Magnetic Resonance Imaging (MRI)
  • Lumbosacral 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 actual radiologic imaging of the coccyx at all.
  • Lumbosacral MRI would be most helpful in cases where 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 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 overall history and physical so that the physician can make an educated determination as to whether the lumbosacral MRI findings represent actual pain generators or incidental findings.
• Bone scan and computed tomography (CT) scan of the coccyx
  • In cases of suspected fracture with negative or inconclusive plain radiographic findings, bone or CT scanning could 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.
  • In most cases of coccydynia, bone and CT scanning are not necessary.
  • These studies can be considered particularly in medicolegal cases where objective evidence is needed regarding the presence or absence of a coccygeal fracture or in cases where bony cancer or metastases are being considered.
• CT scanning and/or MRI of the pelvis⁸
  • CT scanning and/or MRI of the pelvis can be helpful in cases where intrapelvic pathology (ovarian, cervical, colon, testicular, or prostate cancer or their associated metastases) is suspected.
  • 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 at showing pathology of the ovaries, uterus, prostate, urinary bladder, and bowels.
  • Also, unlike MRI, CT scanning carries notable risks of radiation exposure.

Other Tests

• Electromyography (EMG) and nerve conduction studies (NCSs)
  • EMG and NCSs are usually unnecessary in cases of isolated coccydynia.
  • Electrodiagnostics are potentially helpful in cases where concomitant lumbosacral radiculopathy is suspected.

Procedures

• The patient's response to injection of local anesthetic agents, with or without corticosteroids, can provide helpful information regarding whether the patient's actual 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. See Treatment for further details regarding these injections.
• One case series indicates that a positive coccygeal discogram is correlated with better outcome from surgery, but these results were based on small numbers, including just 2 surgical patients who had positive preoperative discograms and 2 surgical patients who had negative preoperative discograms.⁹ Further, the usefulness of a positive discogram at predicting surgical outcome intuitively seems to be contraindicated by a separate, histologic study showing that disc degeneration at the sacrococcygeal joint in 5 patients was associated with poor surgical outcome in all 5 cases.¹⁰

Histologic Findings

A single case series of 8 patients that 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

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