Heterotopic Ossification

Topic updated on 08/07/16 3:06pm
  • Formation of bone in atypical, extraskeletal tissues
    • usually occurs
      • spontaneously or following trauma
      • within 2 months of neurologic injury (brain or spinal cord)
    • most common location is between muscle and joint capsule
  • Epidemiology
    • incidence
      • (see table below)
    • demographics
      • male:female = 2:1
      • especially men with hypertrophic osteoarthritis, and women >65y
    • location
      • traumatic brain injury or stroke
        • hip > elbow > shoulder > knee
        • elbow HO more common following brain trauma  
        • occurs on affected (spastic) side
        • rarely in the knee (TBI)
      • spinal cord injury 
        • hip > knee > elbow > shoulder
        • hip flexors and abductors > extensors or adductors
        • medial aspect of the knee
    • risk factors 
      • (see table below)
  • Pathophysiology
    • exact cause of HO is not known but there appears to be a genetic disposition
    • experimental HO associated with
      • tissue expression of BMP
  • Associated conditions
    • orthopaedic manifestations
      • pathologic fractures
        • from decreased joint ROM and osteoporotic bone
      • nerve impingement
      • soft tissue contractures, contributing to the formation of decubitus ulcers
      • CRPS (more common in patients with HO)
      • joint ankylosis
      • HO after THA adversely affects outcome of THA
    • nonorthopaedic conditions
      • skin maceration and hygiene problems
Risk Factors for Heterotopic Ossification
Injury severity score (ISS) q   High ISS is a risk 11%
Traumatic brain injury (TBI) Higher incidence in the spastic limbs of the patient      11%
Spinal cord injury Complete SCI produces more HO than incomplete SCI. Cervical and thoracic SCI produces more HO than lumbar SCI. Younger age produces more HO (20-30yo). Higher incidence in the spastic limbs of the patient.   20%
Neurologic compromise Prolonged coma in young patient (20-30yo), and prolonged ventilator use  
Other diseases
DISH, ankylosing spondylitis, hypertrophic osteoarthritis (prominent osteophytes)
Decubitus ulcers Worse with concomitant decubitus ulcers and SCI or TBI 70% (with concomitant SCI)
Antegrade femoral nail entry site Worse with piriformis fossa entry point. 25%
Distal femur traction pins  HO in distal quadriceps. Higher incidence in patients with other concomitant injuries, use of large diameter Steinmann pins (5mm) because of hematoma, soft tissue injury from percutaneous insertion. rare
Amputation through zone of injury   Worse with blast mechanism  63%
Surgical approaches Extended iliofemoral > Kocher-Langenbeck > ilioinguinal approach (acetabular fracture). Anterior approach > posterior approach for femoral head fracture fixation.  25% (acetabular fracture fixation)
Total hip arthroplasty THA Complications  Increased risk with psoas tenotomy and cementless components (more particulate debris and marrow spillage, muscle trauma from difficult broaching). Smith-Petersen and Hardinge > transtrochanteric > posterior (posterior has lowest risk of HO). 53% (significant in only 5%)
Total knee arthroplasty 

TKA complications  Increased risk with notching anterior femur, surgical trauma to quadriceps, distal femur exposure and periosteal stripping, and postop manipulation under anesthesia, and high lumbar BMD

  • Subtypes
    • neurogenic HO (discussed here)
    • traumatic myositis ossificans 
    • fibrodysplasia ossificans progressiva (Munchmeyer's Disease)
  • Symptoms
    • painless loss of ROM
    • interferes with ADL
    • CRPS symptoms
    • fever
  • Physical exam
    • inspection
      • warm, painful, swollen joint
      • may have effusion
      • skin problems
        • decubitus ulcers
          • from contractures around skin, muscles, ligaments 
        • skin maceration and hygiene problems
    • motion
      • decreased joint ROM
      • joint ankylosis
      • with HO after TKA, might develop quad muscle snapping or patella instability
    • neurovascular
      • peripheral neuropathy
        • HO often impinges on adjacent NV structures
  • Radiographs 
    • recommended views
      • Judet view valuable for evaluation of hip HO
    • findings
      • ossification usually easy to visualize  
      • maturity of HO 
        • the appearance of a bony cortex suggests mature HO
        • sharp demarcation from surrounding tissue
        • trabecular pattern
    • sensitivity and specificity
      • not useful for early diagnosis
      • only useful at 1 week after onset of symptoms
        • calcium is deposited 7-10 days later than symptom onset
  • Ultrasound 
    • indications
      • for early diagnosis of hip HO  
    • findings
      • echogenic surfaces with posterior acoustic shadowing
  • CT 
    • indications
      • useful for preoperative planning 
  • Triphasic bone scan 
    • indications
      • best for early diagnosis  
      • most commonly used diagnostic study
  • Labs
    • elevated serum alkaline phosphatase (>250IU/L)
      • ALP removes inhibitors of mineralization
      • nonspecific, may be elevated with skeletal trauma
      • cannot determine maturity of HO
      • elevated 12wks after surgery is predictor
    • elevated CRP
      • correlates with inflammatory activity of HO better than ESR
      • normalization of CRP may correlate with maturity of HO
    • elevated ESR (>35mm/h)
      • 12wks after THA is predictor
    • elevated CK
      • correlates with involvement of muscle, extent of muscle involvement
  • Histology
    • mature fatty bone marrow
    • mature trabecular bone
  • Prophylaxis
    • bisphosphonates & NSAIDS
      • indications
        • although no literature supports, are commonly used
      • technique
        • indomethacin is most commonly used
          • dose is 75mg/day for 10days to 6 weeks
    • perioperative radiation
      • indications
        • although no literature supports, commonly used
        • is thought to be effective by blocking osteoblast differentiation
      • technique
        • a single perioperative dose of 700cGy can be given either 4 hours preop or within 72 hours postoperatively 
        • <550cGy not effective
  • Posttraumatic
    • wide exposure and surgical resection 
      • indications
        • severe loss of motion and decreased function
      • technique
        • wide exposure required to identify all neurovascular structures that may be involved
      • timing of resection (controversial)
        • marked decrease in bone scan activity AND normalization of ALP
        • 6 months following general trauma
        • 1 year following SCI
        • 1.5 years following TBI
          • some data suggests equivalent results when comparing early versus late resection
      • postop
        • follow with 5 day course of indomethacin
        • early gentle joint mobilization
  • Arthroplasty
    • treatment for HO following THA 
    • treatment for HO following TKA 
  • Hematoma and intraoperative bleeding
  • Infection
    • higher rate of infection following joint arthroplasty if HO is present
  • Fractures of osteoporotic bone
    • osteopenic from disuse
    • during surgery or physiotherapy
  • Recurrence
    • recurrence rate correlates with neurological injury
      • greater recurrence if severe neurological compromise
  • AVN 
    • if extensive dissection or stripping is required
B. Scan

Case A

Case B hip              
(1) - histology does not always correspond to case


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Qbank (6 Questions)

(OBQ12.125) A 24-year-old male presents with a painful, stiff elbow after sustaining an injury 4 months ago. A radiograph is shown in Figure A. Which of the following statements is true about his condition? Topic Review Topic
FIGURES: A          

1. Early excision has been found to decrease rate of recurrence compared to excision after maturity
2. Radiographs may be used to assess maturity of the lesion
3. Bone scan will always be negative once the lesion is considered mature
4. The lesion is considered mature 12 months after initial radiographic findings are seen
5. Alkaline phosphatase level measurements are used to determine the maturity of the lesion

(OBQ09.135) A 27-year-old man is involved in a motor vehicle crash and sustains a closed head injury and right intertrochanteric hip fracture with ipsilateral femoral head fracture. He undergoes operative stabilization of his right hip. At 1 year follow-up he has limited rotation and abduction of the hip. Radiographs are shown in Figures A and B. What intervention during his initial treatment could have potentially prevented this outcome? Topic Review Topic
FIGURES: A   B        

1. 700 cGy of radiation within 72 hours of surgery
2. Pulsed administration of recombinant PTH 1,34 postoperatively for 1 year
3. 3 cycles of VAC (Vincristine, Actinomycin D, and Cyclophosphamide)
4. 700 cGy of radiation 2 weeks prior to surgery
5. 3 treatments of 700 cGy of radiation divided over 1 week after surgery

(OBQ07.68) Which amputation patient would have the highest risk of developing heterotopic ossification at the amputation site? Topic Review Topic

1. 75-year-old diabetic with an ischemic limb undergoing a transtibial amputation
2. 45-year-old woman that had a propane tank explode near her thigh undergoing a transfemoral amputation
3. 25-year-old army captain with a complex blast injury to his shin undergoing transfemoral amputation
4. 65-year-old with necrotizing fasciitis of his lower leg undergoing knee transfemoral amputation
5. 35-year-old woman with a grade IIIC open distal tibia fracture who elects for a below the knee amputation

(OBQ07.159) Heterotopic ossification has been recognized as a rare complication from Steinmann pins placed in which location for traction purposes? Topic Review Topic

1. distal femur
2. proximal tibia
3. calcaneus
4. radius shaft
5. metacarpal shaft

(OBQ05.61) Which of the following has not been shown in the literature to increase the risk of heterotopic ossification? Topic Review Topic

1. Prolonged ventilator time in multiply traumatized patients
2. Spinal cord injury
3. Amputation through the zone of injury in patients injured in blasts
4. Open fractures
5. Severe burns

(OBQ04.8) A 32-year-old male sustains a the injury shown in Figure A after a high-speed motor vehicle collision. Which factor has been found to have the highest direct correlation with severe heterotopic ossification after traumatic knee dislocation? Topic Review Topic
FIGURES: A          

1. Injury Severity Score (ISS)
2. Glascow Coma Scale (GCS)
3. Timing of knee reconstruction
4. Number of ligaments reconstructed
5. Open ligament reconstruction



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