What is the most likely diagnosis for a 15‑year‑old female who sat hard on a rock causing coccygeal pain that resolved after three months, then redeveloped severe coccygeal pain worsened by sitting and standing for three weeks, without swelling, redness, or palpable deformity?

Post-Traumatic Coccydynia with Delayed Recurrence

This is most likely post-traumatic coccydynia with coccygeal instability or hypermobility, presenting as a delayed recurrence after the initial trauma. 1, 2, 3

Clinical Diagnosis

The presentation is classic for traumatic coccydynia:

• Direct trauma to the coccyx (falling hard on a rock)
• Pain exacerbated by sitting and transitioning from sitting to standing
• Initial resolution followed by delayed recurrence at 3 months
• No visible external signs (no redness, swelling, or palpable deformity)

The delayed recurrence after complete resolution is a recognized pattern in post-traumatic coccydynia, where initial healing may be followed by development of mechanical instability or chronic inflammation 1, 2, 3. In adolescents, poor intercoccygeal joint stability and coccygeal hypermobility are particularly common causes 4.

Pathophysiology

The most likely underlying mechanisms are:

1. Coccygeal hypermobility or instability - The initial trauma may have damaged intercoccygeal ligaments, leading to abnormal motion that becomes symptomatic over time 5, 2, 3

2. Anterior angulation of the coccyx - Trauma can cause persistent malalignment that may not be immediately symptomatic but becomes painful with repetitive microtrauma from sitting 1, 6

3. Chronic inflammation - Ongoing mechanical irritation at the sacrococcygeal or intercoccygeal joints 2, 7

Diagnostic Workup Required

Standard anteroposterior and lateral radiographs should be obtained first to exclude fracture, dislocation, or serious pathology 7. However, static radiographs are often normal in coccydynia.

Dynamic sitting-standing lateral radiographs are the reference standard and should be performed when mechanical pain is suspected and symptoms persist 5, 2, 7. These reveal pathologic coccygeal motion (hypermobility >25° or rigid/immobile coccyx) that correlates with pain 3, 7.

Cross-sectional imaging (MRI or CT) is reserved for:

• Red-flag features (fever, weight loss, neurologic symptoms)
• Suspected neoplasm or infection
• Trauma with concern for occult fracture
• Inconclusive basic imaging 7

In this 15-year-old with clear trauma history and typical symptoms, dynamic radiographs are the next appropriate step 5, 2, 7.

Management Algorithm

First-Line Conservative Treatment (3-6 months):

1. Education and offloading strategies:

   • Avoid prolonged sitting
   • Use a coccygeal cushion (donut or wedge-shaped with coccygeal cutout) 1, 2, 7
   • Lean forward when sitting to reduce coccygeal pressure 7

2. Pharmacologic management:

   • NSAIDs or acetaminophen for analgesia 1, 2, 6
   • Topical analgesics may provide additional benefit 5, 2

3. Physiotherapy:

   • Pelvic floor training and manual therapy 2, 7
   • Extracorporeal shock wave therapy has the strongest evidence among conservative modalities 7

Conservative treatment should be tried for at least 3-6 months before considering interventional options 2, 7.

Second-Line Interventional Treatment:

If conservative measures fail after 3-6 months:

1. Image-guided corticosteroid injection (local infiltration or ganglion impar block) - Can provide marked symptom improvement in many patients 2, 3, 7

2. Radiofrequency procedures - For persistent cases 2, 7

Third-Line Surgical Treatment:

Coccygectomy should only be considered for:

• Chronic, function-limiting pain (typically >6-12 months)
• Failed conservative and interventional care
• Demonstrated coccygeal instability on dynamic imaging
• Positive response to diagnostic blocks 2, 7

In a meta-analysis, coccygectomy provided pain relief in 84% of patients, with 76% returning to work, though 5% experienced wound dehiscence and 3% required repeat surgery 2.

Critical Pitfalls to Avoid

1. Do not assume normal static radiographs exclude pathology - Dynamic imaging is essential to detect hypermobility 5, 2, 3, 7

2. Do not rush to surgery - Conservative treatment must be exhausted first, as most patients improve with non-operative management 1, 2, 7

3. Do not overlook red-flag features requiring advanced imaging:

   • Constitutional symptoms (fever, weight loss)
   • Neurologic deficits
   • Night pain
   • Progressive worsening despite treatment 7

4. In adolescents, consider anatomical variations - Rare developmental anomalies of the coccyx can cause symptoms 4

Prognosis

With appropriate conservative treatment, this patient has a good prognosis. The case report of a similar 34-year-old with post-traumatic anterior coccygeal angulation showed pain reduction from 7/10 to 2/10 at 3 months with conservative care alone 1. In pediatric cases, caudal epidural blocks have shown effectiveness when conservative measures fail 6.