What is heterotopic ossification?
Heterotopic ossification (HO) refers to the presence of bone in soft tissue where bone normally does not exist. The acquired form of HO most frequently is seen with either musculoskeletal trauma, spinal cord injury, or central nervous system injury.
There are bilateral total hip arthroplasties in situ, cemented on the right, uncemented on the left.
Right side: The femoral head is asymmetrical in the acetabular cup indicating loss of polyethylene liner laterally and superiorly. There is lucency at the bone cement interface along the lateral margin of the right femoral prosthesis. Lucency is seen at the cement prosthesis interface along the distal femoral component. Heterotopic ossification is seen arising mainly from the lateral acetabulum with >1 cm between opposing surfaces of bone.
Left side: Heterotopic bone extends from the acetabulum across to the greater trochanter, giving the appearance of ankylosis.