Is a 3.3 mm posterior displacement of S5 in relation to S4 considered a coccygeal (tailbone) fracture?

Posterior Displacement of S5 in Relation to S4 as a Coccygeal Fracture

A 3.3 mm posterior displacement of S5 in relation to S4 is considered a coccygeal (tailbone) fracture. This represents a specific type of fracture pattern in the sacrococcygeal region that requires appropriate diagnostic evaluation and management.

Diagnostic Considerations

• CT imaging is the most appropriate modality for detailed evaluation of coccygeal fractures, as it provides superior identification and clarification of fracture morphology compared to conventional radiographs 1
• Posterior displacement of S5 in relation to S4 specifically represents a type of compression fracture that can occur at the sacrococcygeal junction 2
• This type of fracture may be classified as an "adolescent compression fracture of S5" (type 2b) according to established classification systems, characterized by compression of the sacral extremity 2
• MRI may be indicated as a supplementary imaging modality when there is concern for associated soft tissue injuries or when persistent pain requires further evaluation 1, 3

Clinical Implications

• Coccygeal fractures with displacement are often unstable and may lead to chronic pain (coccygodynia) if not properly diagnosed and managed 2, 4
• The posterior displacement pattern seen in this case indicates potential instability that may require more aggressive management than non-displaced fractures 4
• Abnormal mobility of the coccyx, which can be visualized on dynamic radiographs (lateral X-rays in standing and sitting positions), is the most common pathological finding in patients with coccygodynia (70% of cases) 5
• The degree of displacement (3.3 mm in this case) is clinically significant and suggests a true fracture rather than a normal anatomical variant 2

Management Approach

• Initial management should be conservative, including rest, analgesics, cushioning when sitting, and physical therapy 5, 6
• For persistent pain despite conservative measures, more invasive interventions may be considered, including:
  • Local anesthetic and corticosteroid injections into painful structures 5
  • Radiofrequency ablation of coccygeal discs 5
  • Extracorporeal shockwave therapy 6
• Surgical intervention (partial or total coccygectomy) should be reserved for refractory cases, particularly those with abnormal mobility or displacement that fail to respond to conservative treatment 5, 4
• Total coccygectomy has shown better outcomes than partial coccygectomy for cases of traumatic instability 4

Common Pitfalls and Caveats

• Misdiagnosis is common as coccygeal fractures may be mistaken for simple contusions or normal anatomical variants 3
• Conventional radiographs alone may miss subtle fractures or displacements; CT imaging provides superior visualization of the sacrococcygeal region 1, 2
• Persistent pain following coccygeal trauma should prompt further evaluation rather than continued conservative management without additional diagnostic workup 3, 4
• The natural history of coccygeal fractures varies; while many heal spontaneously, those with significant displacement (as in this case) often remain unstable and may require more aggressive intervention 2