What is the most appropriate initial imaging study for persistent coccygeal pain three months after trauma: a plain lateral coccygeal radiograph or a computed tomography (CT) scan?

Imaging for Persistent Coccygeal Pain 3 Months Post-Trauma

Start with dynamic lateral radiographs (standing and sitting views) as the initial imaging study for persistent coccygeal pain 3 months after trauma, and proceed to CT or MRI if radiographs are negative but clinical suspicion remains high. 1, 2, 3

Initial Imaging Approach

Dynamic radiography is the preferred first-line imaging modality for evaluating post-traumatic coccydynia. 1, 2, 3 This differs from standard static radiographs and requires specific positioning:

• Obtain lateral views in both standing and sitting positions to assess for pathologic coccygeal motion and hypermobility that may not be visible on static films 1, 3
• Dynamic imaging reveals hypermobility defined as >25% posterior subluxation or >25° flexion while sitting, with >35° posterior subluxation considered significant 1
• Static neutral radiographs commonly appear normal in post-traumatic coccydynia, making dynamic views essential for diagnosis 3

When to Advance to Cross-Sectional Imaging

If dynamic radiographs are negative or inconclusive but clinical suspicion remains high, proceed to CT or MRI rather than obtaining additional radiographic projections. 4, 2, 3

CT Indications and Findings

• CT excels at detecting subtle fractures, bony spicules, and morphologic abnormalities that predict coccydynia 1, 3
• Key CT findings include Type II coccyx morphology, intercoccygeal joint subluxation, and presence of bony spicules 1
• CT can reveal coccygeal pathology in patients where plain films are inconclusive 4

MRI Indications and Findings

• MRI is superior for evaluating soft tissue pathology, bone marrow edema, and inflammatory changes in the sacrococcygeal region 4, 2, 3
• MRI can identify radiographically occult sources of pain including ligamentous injury, disc pathology, and bone marrow signal changes 4, 3
• MRI helps differentiate coccydynia from other conditions (neoplasm, infection, crystal deposition, pilonidal cyst) that may cause similar symptoms 3

Clinical Context at 3 Months Post-Trauma

At 3 months post-trauma, you are evaluating for post-traumatic instability (hypermobility, subluxation, or fracture-dislocation) that may have been missed acutely or developed over time. 5, 2

• Post-traumatic coccydynia that persists beyond conservative management warrants aggressive imaging evaluation 5
• Coccygeal fractures are classified as flexion type 1, compression type 2, and extension type 3 1
• One-third of coccydynia cases are idiopathic, requiring thorough imaging to exclude structural pathology 1

Common Pitfalls to Avoid

• Do not rely on static radiographs alone – they miss pathologic motion and hypermobility that are common causes of persistent pain 1, 3
• Do not skip dynamic positioning – standing and sitting views are essential, not optional 1, 2
• Do not delay cross-sectional imaging when clinical suspicion is high despite negative radiographs, as this leads to prolonged symptoms and multiple physician visits 4, 1
• Recognize that coccydynia is frequently overlooked and mistaken for lumbosacral, pelvic, or gastrointestinal pathology 2

Treatment Implications

Imaging findings directly guide treatment decisions:

• Conservative management (cushions, NSAIDs, physical therapy) for mild cases 4
• Image-guided interventions (ganglion impar block, sacrococcygeal joint injections) for moderate cases 2, 3
• Total coccygectomy for refractory post-traumatic instability has high success rates, with partial coccygectomy associated with poor results 5