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Updated: Jun 22 2021

Heterotopic Ossification

Images
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  • summary
    • Heterotopic Ossification is the formation of bone in atypical, extraskeletal tissues that may occur following localized trauma, following a neurological injury, or as a post-surgical complication. Patients typically present with painless loss of motion of the affected joint. 
    • Diagnosis is made radiographically with soft tissue ossification with sharp demarcation from surrounding soft tissues.
    • Treatment is focused on prevention with oral indomethacin and perioperative radiation. Surgical excision is indicated in the presence of mature lesions associated with severe loss of motion and function. 
  • Epidemiology
    • Incidence
      • (see table below)
    • Demographics
      • male:female = 2:1
      • especially men with hypertrophic osteoarthritis, and women >65y
    • Anatomic location
      • most common location is between muscle and joint capsule
      • 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)
  • Etiology
    • Forms
      • usually occurs
        • spontaneously or following trauma
        • within 2 months of neurologic injury (brain or spinal cord)
        • following THA and TKA
    • 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)
      • 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
      • Burns
      • Both locally under burn and remotely.
      • More common with >20% body surface area
      • 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
      • Higher incidence with 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
      • 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 the lowest risk of HO).
      • 53% (significant in only 5%)
      • Total knee arthroplasty
      • 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
      • Other diseases
      • DISH
      • Ankylosing spondylitis
      • Hypertrophic osteoarthritis (prominent osteophytes)
  • Classification
    • Subtypes
      • neurogenic HO (discussed here)
      • traumatic myositis ossificans
      • fibrodysplasia ossificans progressiva (Munchmeyer's Disease)
  • Presentation
    • 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
  • Imaging
    • 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
  • Studies
    • 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
  • Treatment
    • Prophylaxis
      • Indomethacin
        • indications
          • although no literature supports, are commonly used
        • technique
          • indomethacin is most commonly used
            • dose is 75mg/day for 10 days 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
          • irradiation
    • Arthroplasty
      • treatment for HO following THA
      • treatment for HO following TKA
  • Complications
    • 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
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