Forty-eight post-traumaticbrain-injured patients in postcoma-unawareness (PC-U) state, are included in this study. All recovered consciousness at least 1 month after the accident. The muscular tone and movement of all limbs was examined. At least two X-rays of the big joints were taken. Periarticular new bone formation appeared in 26 patients. This heterotopic ossification occurs in severely injured patients, primarily in proximal joints of the upper and lower extremities. Their aetiology in brain injury is unknown. Risk factors include prolonged coma, tone and movements in the involved extremity, and associated fractures. We found that the appearance of periarticular new bone formation had a close correlation with pathological movement (paresis or plegia), a borderline correlation with hypertonus, and no correlation with hypotonus or with associated fractures.