Table 1

Brooker classification of heterotopic ossification [6]

Grade 1

Islands of bone within the soft tissues about the hip

Grade 2

Bone spurs from the pelvis or proximal end of the femur, leaving at least one centimeter between opposing bone surfaces

Grade 3

Bone spurs from the pelvis or proximal end of the femur, reducing the space between opposing bone surfaces to less than one centimeter

Grade 4

Apparent bone ankylosis of the hip

Baird and Kang Journal of Orthopaedic Surgery and Research 2009 4:12   doi:10.1186/1749-799X-4-12