Heterotopic Ossification M61.9 728.10


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)
  • DISH
  • Past hx of heterotopic bone
  • Hypertrophic osteoarthritis
  • Paget's disease
  • Post-traumatic arthritis
  • Osteonecrosis
  • 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 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 or Indomethacin 25 mg TID for 3-6 weeks (contraindated for renal insufficiency)
  • single fraction dose about 700-800 centigrey of radiation (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.  Consider surgical resection once mature. 
    -Grade 4: ankylosis.   Consider surgical resection once mature. 
  • 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

  1. Seegenschmiedt MH, Makoski HB, Micke O, et al: Radiation prophylaxis for heterotopic ossification about the hip joint: A multicenter study. Int J Radiat Oncol Biol Phys 2001;51:756-765.
  2. Pakos EE, Ioannidis JP: Radiotherapy vs nonsteroidal anti-inflammatory drugs for the prevention of heterotopic ossification after major hip surgery: A meta-analysis of randomized trials. Int J Radiat Oncol Biol Phys 2004;60:888-895.
  3. Kolbl O, Knelles D, Barthel T, et al: Preoperative irradiation versus the use of nonsteroidal anti-inflammatory drugs for prevention of heterotopic ossification following total hip replacement: The results of a randomized trial. Int J Radiat Oncol Biol Phys 1998;42:397-401.