Heterotopic ossification after central nervous system trauma: A current review

Abstract

Neurogenic heterotopic ossification (NHO) is a disorder of aberrant bone formation affecting one in five patients sustaining a spinal cord injury or traumatic brain injury. Ectopic bone forms around joints in characteristic patterns, causing pain and limiting movement especially around the hip and elbow. Clinical sequelae of neurogenic heterotopic ossification include urinary tract infection, pressure injuries, pneumonia and poor hygiene, making early diagnosis and treatment clinically compelling. However, diagnosis remains difficult with more investigation needed. Our pathophysiological understanding stems from mechanisms of basic bone formation enhanced by evidence of systemic influences from circulating humor factors and perhaps neurological ones. This increasing understanding guides our implementation of current prophylaxis and treatment including the use of non-steroidal anti-inflammatory drugs, bisphosphonates, radiation therapy and surgery and, importantly, should direct future, more effective ones.

Keywords: Heterotopic ossification; Neurogenic; Neurohumoral; Osteogenesis; Prophylaxis; Spinal cord injury; Traumatic brain injury.

Fig. 1

Diagram depicting the complex and poorly understood interplay between neurohumoral factors and the development of heterotopic bone formation. At the centre is the stimulation of osteoblasts to lay down ectopic bone.

Fig. 2

A 40-year-old male patient sustained an American Spinal Injury Association (ASIA) grade-A spinal cord injury from a gunshot at the level of T10. At five years after injury, three-dimensional CT images show massive bilateral heterotopic ossification (HO) of the hips with joint ankylosis. Complications of the extensive HO include recalcitrant sacral pressure ulcers and an inability to sit in a wheelchair.

Fig. 3

A 37-year-old male patient sustained a fracture of the left acetabulum and traumatic brain injury after a high-speed automobile collision. The patient underwent open reduction and internal fixation of the left acetabular fracture within four days of the injury. Anteroposterior radiograph (left) and CT (right) were taken six months after injury and show the sciatic nerve encased in heterotopic bone (arrow). Advanced imaging was essential for diagnosis and pre-operative planning for surgical resection.