synonyms: HO, heterotopic ossification
- 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.
- Occurs in 64.6% of high-energy wartime extremity injuries. Risk factors = brain injury, age <30, an amputation, multiple extremity injuries, ISS >16 (Forsberg JA, JBJS 2009;91A:1084)
HO Risk Factores
- Males c ankylosing spondylitis (occurs is 23% of pts with ankylosing spondylitis undergoing THA)
- Past hx of heterotopic bone
- Hypertrophic osteoarthritis
- Paget's disease
- Post-traumatic arthritis
- Rheumatoid arthritis
- Wartime Risk factors = brain injury, age <30, an amputation, multiple extremity injuries, ISS >16 (Forsberg JA, JBJS 2009;91A:1084)
HO Clinical Evaluation
- May present with pain, swelling, warmth, and/or loss of motion.
- 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.
- Indomethacin 75mg QD or Indomethacin 25 mg TID for 3-6 weeks
- 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.
- Kjaersgaard-Andersen classification: (Kjaersgaard-Andersen P, J Arthroplasty 1989;4:99)
HO Review References