Sacral osteoblastoma masquerading as sacroiliac joint dysfunction: A case report

BACKGROUND: Lumbosacral pain is a common musculoskeletal complaint that is typically mechanical in nature. However, rare conditions such as osteoblastoma can mimic benign spinal pain, leading to diagnostic delays and protracted care. CASE PRESENTATION: An 18-year-old male college student presented to physical therapy, via direct access, with persistent right-sided lumbosacral pain of 6 weeks. His pain worsened with general activity and lying supine. Clinical examination was pathognomonic of sacroiliac (SI) joint dysfunction, and clinical guidelines did not indicate a need for imaging. Four weeks of conservative management for presumed SI joint dysfunction was initiated and included mobilization, stabilization exercises, and use of an SI support belt. Despite adherence to an evidence-based plan of care, the patient failed to demonstrate clinically important improvement in pain and function based on previously established minimal clinically important difference thresholds. The patient ultimately, over the course of care, exhibited intermittent difficulty with bladder voiding and was referred to his family physician and ultimately a surgeon for further evaluation. DIAGNOSIS: Subsequent magnetic resonance imaging (MRI) and computed tomography (CT) revealed a lobulated, multi-cystic lesion involving the right sacrum extending into the S1 and S2 neural foramina. A CT-guided biopsy confirmed the diagnosis of osteoblastoma with secondary aneurysmal bone cyst features. Intervention: The patient underwent surgical excision of the tumor with decompression of the S1-S2 nerve roots. A multidisciplinary team including orthopedic and neurosurgical specialists performed the procedure without complication. OUTCOMES: Postoperative recovery was uneventful, and follow-up MRI at 6 months and 1 year showed no evidence of recurrence. The patient, via telephone communication, reported resolution of symptoms and pre-morbid return to function at the 1-year post-operative period. CONCLUSION: This case underscores the importance of considering red flags when patients are recalcitrant to standard interventions. A poor response to conservative care should prompt a referral for imaging.