Dynamic Radiographs (Sitting and Standing Views)
For a 41-year-old woman with chronic coccygeal pain lasting over one year, dynamic radiographs of the coccyx in sitting and standing positions are the first-line imaging investigation. 1, 2, 3
Rationale for Dynamic Radiographs
Dynamic radiographs remain the reference standard for evaluating coccygeal pathology because they:
- Assess coccygeal mobility and instability during positional changes, which is the most common pathophysiologic mechanism in coccydynia 2, 3
- Identify hypermobile or rigid coccyx configurations that correlate with symptom severity 3
- Detect coccygeal spicules (bony projections) that can cause localized pain 3, 4
- Exclude fractures or gross structural abnormalities from trauma 1
The sitting-to-standing comparison is critical because it reveals dynamic instability that static films miss—this is what differentiates functional coccygeal pain from other causes.
When to Consider Advanced Imaging
MRI should be obtained if:
- Dynamic radiographs are normal but symptoms persist
- Red flag features are present (fever, weight loss, neurologic symptoms, history of malignancy)
- Trauma history suggests soft tissue injury
- You need to exclude tumor, infection, or inflammatory pathology 1, 2, 3
MRI can demonstrate disc signal changes, bone marrow edema, bursitis around the coccyx tip, and soft tissue pathology not visible on plain films 4. In one adolescent series, 11/27 MRI scans showed disc or bone hypersignal and 6/27 showed bursitis 4.
CT is reserved for:
- Detailed bony anatomy assessment when surgery is being considered
- Suspected fracture not clearly seen on radiographs
- Preoperative planning 1
Common Pitfall to Avoid
Do not start with MRI or CT as your first test. While these provide excellent anatomic detail, they don't assess the dynamic mechanical component that is central to most coccydynia cases 2, 3. Starting with static cross-sectional imaging misses the functional instability that dynamic radiographs reveal and may lead to unnecessary advanced imaging costs without diagnostic yield.
Clinical Context
The physical examination finding of focal tenderness on direct palpation of the coccyx (performed rectally or externally) combined with pain worse with sitting and sit-to-stand transitions makes the diagnosis highly likely 1, 2, 5. Dynamic radiographs then confirm the mechanical basis and guide treatment decisions—conservative management for mild instability versus interventional procedures or surgery for severe cases 2.
Women are affected 5 times more frequently than men, and trauma (including childbirth) is identified in approximately 37-40% of cases 2, 4.