BACKGROUND: Myositis ossificans is a non-neoplastic benign reactive bone and cartilage matrix-producing pseudotumor that develops in skeletal muscles adjacent to the joint. The clinical and pathologic appearance of myositis ossificans varies depending on the time elapsed after heterotopic bone formation. Although its etiology is unclear, it usually occurs at the site of the injured muscle, most commonly in large muscles of the extremities, especially the quadriceps and brachialis. It rarely occurs in the paravertebral muscle of the lumbar spine.

CASE REPORT: We present the rare case of a 31-year-old Turkish man with calcifying myositis ossificans not associated with trauma, referred to our hospital with severe low back pain with restriction of low back motions. Radiological investigation suggested a sclerotic osteoblastic on the left facet joint of L4–5. To confirm the diagnosis, the patient was managed surgically by total excision of the mass, which resulted in a good functional recovery. At his 12-month follow-up examination, he was neurologically intact and no recurrence was seen.

CONCLUSIONS: Cases like this should be investigated well, so careful correlation of the clinical and radiologic findings with taking a biopsy is necessary to confirm diagnosis.

Keywords: Diagnosis, Differential, Biopsy, Low Back Pain - etiology, Lumbar Vertebrae, Magnetic Resonance Imaging, Myositis Ossificans - diagnosis