Updated: 6/22/2021

Heterotopic Ossification

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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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(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?

QID: 4485
FIGURES:
1

Early excision has been found to decrease rate of recurrence compared to excision after maturity

5%

(203/4344)

2

Radiographs may be used to assess maturity of the lesion

46%

(2007/4344)

3

Bone scan will always be negative once the lesion is considered mature

19%

(828/4344)

4

The lesion is considered mature 12 months after initial radiographic findings are seen

18%

(780/4344)

5

Alkaline phosphatase level measurements are used to determine the maturity of the lesion

11%

(489/4344)

L 4 C

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(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?

QID: 2948
FIGURES:
1

700 cGy of radiation within 72 hours of surgery

89%

(1494/1671)

2

Pulsed administration of recombinant PTH 1,34 postoperatively for 1 year

1%

(22/1671)

3

3 cycles of VAC (Vincristine, Actinomycin D, and Cyclophosphamide)

1%

(15/1671)

4

700 cGy of radiation 2 weeks prior to surgery

1%

(19/1671)

5

3 treatments of 700 cGy of radiation divided over 1 week after surgery

7%

(113/1671)

L 1 C

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

QID: 729
1

75-year-old diabetic with an ischemic limb undergoing a transtibial amputation

3%

(31/1186)

2

45-year-old woman that had a propane tank explode near her thigh undergoing a transfemoral amputation

62%

(738/1186)

3

25-year-old army captain with a complex blast injury to his shin undergoing transfemoral amputation

28%

(328/1186)

4

65-year-old with necrotizing fasciitis of his lower leg undergoing knee transfemoral amputation

2%

(19/1186)

5

35-year-old woman with a grade IIIC open distal tibia fracture who elects for a below the knee amputation

5%

(64/1186)

L 3 B

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

QID: 820
1

distal femur

82%

(1908/2336)

2

proximal tibia

5%

(110/2336)

3

calcaneus

4%

(102/2336)

4

radius shaft

7%

(175/2336)

5

metacarpal shaft

1%

(33/2336)

L 2 B

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

QID: 947
1

Prolonged ventilator time in multiply traumatized patients

13%

(414/3301)

2

Spinal cord injury

11%

(350/3301)

3

Amputation through the zone of injury in patients injured in blasts

5%

(166/3301)

4

Open fractures

57%

(1880/3301)

5

Severe burns

15%

(484/3301)

L 4 B

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(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?

QID: 119
FIGURES:
1

Injury Severity Score (ISS)

40%

(751/1855)

2

Glascow Coma Scale (GCS)

43%

(791/1855)

3

Timing of knee reconstruction

5%

(88/1855)

4

Number of ligaments reconstructed

5%

(101/1855)

5

Open ligament reconstruction

6%

(110/1855)

L 4 B

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