Heterotopic Ossification

synonyms: HO, heterotopic ossification

HO ICD-9

• 728.10 (muscular calcification and ossification, unspecified)

HO Etiology / Epidemiology / Natural History

• Definition: bone formation that occurs in soft tissues.
• Etiology: unknown. Presumed to be caused by pluipontential mesenchymal cell differentiation into osteoblasts.
• Males > females.
• Typically matures 6 months following the inciting event.

HO Risk Factores

• Males c ankylosing spondylitis (occurs is 23% of pts with ankylosing spondylitis undergoing THA)
• DISH
• Past hx of heterotopic bone
• Hypertrophic osteoarthritis
• Paget's disease
• Post-traumatic arthritis
• Osteonecrosis
• Rheumatoid arthritis

HO Clinical Evaluation

• May present with pain, swelling, warmth, and/or loss of motion.

HO Xray

• HO is generally diagnosed with xrays of involved area. Initialy HO is seen as a fluffy opacity which matures to that of bone in 3-5 months. First appears on plain films at 4-6 weeks.

HO Prophylaxis

• Indomethacin 75mg QD for 6wks vs single fraction dose about 700-800 rads given within 72 hours postop had 2% incidence of H.O.(Lewallen DG: Heterotopic Ossification following total hip arthroplasty. Instr Course Lect 1995;44:287-292).

HO Classification / Treatment

• Brooker Classification (Brooker AF, JBJS 1973;55A:1629)
  -Grade 1: Islands of bone within the soft tissues about the hip. Typically asymptomatic.
  -Grade 2: Bone spurs in the pelvis or the proximal end of the femur with at least 1c, between the opposing bone surfaces. Typically asymptomatic.
  -Grade 3: Bone spurs from the pelvis of proximal end of the femur with <1cm between opposing bone structures.
  -Grade 4: ankylosis.
• Once ossification has begun there are no effective treatments to halt or decrease amount of HO.
• HO generally matures by 3-5 months after which time surgical resection may be considered.

HO Review References