What X-ray should be ordered for an older adult patient with a history of osteoporosis who has fallen on their coccyx?

X-ray Imaging for Coccyx Fall in Older Adult with Osteoporosis

Order a standing and sitting lateral X-ray of the coccyx (2 views minimum) as the initial imaging study for an older adult with osteoporosis who has fallen on their coccyx. 1, 2, 3

Initial Imaging Approach

Dynamic radiography is the first-line imaging modality for suspected coccyx injury, specifically requiring:

• Lateral view in standing position 3
• Lateral view in sitting position 3
• These dynamic views allow assessment of both fracture and hypermobility (>25% posterior subluxation or >25° flexion while sitting), which is a common cause of coccydynia 3

The clinical indication should specify: "Coccyx pain post-fall, evaluate for fracture; patient with osteoporosis" 2

Why Dynamic Views Matter

Plain radiographs detect the majority of coccyx fractures, but dynamic imaging is critical because:

• Static films miss hypermobility-related pathology in up to one-third of idiopathic coccydynia cases 3
• Flexion-type fractures (most common from falls) typically involve the upper coccyx and may only be visible with positional changes 4
• Compression fractures occur in the middle coccyx when specific morphologic features are present (square/cuneiform Co2 with long straight Co3) 4

Advanced Imaging Considerations

If initial X-rays are negative but clinical suspicion remains high (persistent pain beyond 4 weeks, inability to sit, point tenderness):

• MRI without contrast is the next appropriate study (rated 9/9 by ACR) for detecting occult fractures, bone marrow edema, and soft tissue injuries not visible on plain films 1, 2, 5
• CT without contrast is an alternative (rated 7/9) if MRI is contraindicated, particularly useful for identifying bony spicules, subluxation of intercoccygeal joints, and morphologic features associated with coccydynia 1, 3

Research demonstrates that MRI and CT can reveal coccygeal pathology when X-rays are inconclusive, with case reports showing successful surgical planning based on advanced imaging findings 5

Critical Morphologic Features to Document

The radiologist should assess for:

• Type II coccyx morphology (associated with increased coccydynia risk) 3
• Subluxation of intercoccygeal joints 3
• Presence of bony spicules 3
• Fracture classification: flexion (type 1), compression (type 2), or extension (type 3) 4

Special Considerations for Osteoporotic Patients

This patient population requires additional evaluation beyond coccyx imaging:

• Order DXA scan of lumbar spine and hips to quantify bone mineral density if not done within the past 1-2 years 6, 7
• Obtain laboratory workup to identify secondary causes of osteoporosis 6
• Initiate bisphosphonate therapy (reduces vertebral fractures by 47-48% and hip fractures by 51%) along with calcium 1000-1200mg daily and vitamin D 800 IU daily 6, 7

Common Pitfalls to Avoid

• Do not order only anteroposterior views – lateral projections are essential for coccyx evaluation 2, 3
• Do not skip dynamic (sitting/standing) views – static films miss hypermobility in one-third of cases 3
• Do not dismiss persistent pain with negative X-rays – 30-40% bone destruction is needed before fractures become visible on plain radiographs, necessitating MRI 2, 5
• Do not forget fall risk assessment – conduct multidimensional fall evaluation and implement supervised physical therapy to prevent future fractures 6

Red Flags Requiring Emergency Evaluation

Send to ER immediately if:

• New neurological deficits (bowel/bladder dysfunction, saddle anesthesia) 6
• Severe uncontrolled pain despite analgesia 6
• Signs of infection (fever, erythema) 6
• Hemodynamic instability 8