Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Heterotopic Ossification

Basics
Description
  • Pathologic bone formation as a consequence of direct trauma or central nervous system injuries
  • Bone formed in heterotopic locations such as muscle, subcutaneous tissues, or nerves
  • Most commonly occurs at the hip, elbow, and shoulder joints.
Epidemiology
Less common in children than in adults, and more common in males than in females
 
Incidence
Occurs in 10-20% of patients with central nervous system or traumatic injuries, with an average onset of 2 months after injury.
 
Risk Factors
  • Central nervous system injury
  • Osteoarthrosis
  • Osteophyte formation
  • Surgical approach
  • Previous surgical procedures
  • Trochanteric osteotomy
  • AS
Genetics
No genetic link can successfully predict patient susceptibility to heterotopic ossification.
 
Etiology
  • Traumatic brain injury
  • Spinal cord injury
  • Trauma
Associated Conditions
  • Fibrodysplasia ossificans progressiva
  • Primary osteoma cutis
Diagnosis
Signs and Symptoms
  • Unexplained increase in pain, spasticity, or muscle guarding
  • Decreased ROM
  • Stiffness
  • Radiographic evidence of ectopic bone
Physical Exam
  • Limited ROM is the most common and earliest sign.
  • Erythema, swelling, and signs of inflammation also may be noted.
Tests
Lab
  • Serum alkaline phosphatase levels are elevated.
    • Value begins to rise 2-3 weeks after injury.
    • Although nonspecific and not absolute, elevated serum alkaline phosphatase may be the earliest test for detection.
Imaging
  • On plain radiographs, new bone formation may be 1st visible at 3-6 weeks; but radiographs generally are not confirmatory until 3 months.
  • Bone scans allow for earlier detection and show intense uptake.
  • CT may be used for preoperative planning and to show the zonal pattern: Mineralized in the periphery and lucent in the center.
Pathological Findings
  • Initially, an intense inflammatory response occurs with myofibroblasts and osteoblasts.
  • Such a high degree of cellular activity occurs that the inflammatory response can be mistaken for a neoplasm.
Differential Diagnosis
  • Septic joint
  • Thrombophlebitis
  • Neoplasm in the soft tissues
Treatment
General Measures
  • Joint motion is maintained to allow normal functioning.
  • Most patients are treated successfully with nonoperative measures, including physical therapy, analgesics, and NSAIDs.
  • Few patients require surgical excision.
Special Therapy
Radiotherapy
  • Radiation therapy is ineffective once heterotopic ossification has been documented.
    • When used for prophylaxis, it must be delivered within 72 hours.
Physical Therapy
Use ROM exercises and treatment modalities that are designed to increase joint mobility.
 
Medication
First Line
  • Anti-inflammatories are used to prevent or to lessen the amount of heterotopic ossification formation after the initial insult and to prevent recurrence after surgical excision.
    • Indomethacin, naproxen, or other NSAIDs for 6 weeks
Surgery
  • Surgery is indicated to restore joint motion or to correct contractures in disabled patients.
  • Heterotopic ossification should not be resected earlier than 6 months after injury.
  • Excision after 2 years increases the likelihood of permanent contractures.
  • After resection of heterotopic ossification, patients are treated with low doses of irradiation (must be delivered within 72 hours).
  • Some patients elect to take NSAIDs (e.g., indomethacin) for 6 weeks after resection.
    • For effective prophylaxis, the medications must be taken.
    • Gastric intolerance prevents 10-20% of patients from taking these medications.
Follow-up
Prognosis
  • Prognosis varies, depending on the location of heterotopic ossification and its cause.
  • Most patients with nonneurogenic heterotopic ossification maintain reasonable function and do not require surgical intervention.
Complications
  • Loss of mobility
  • Ankylosis
Patient Monitoring
Serial radiographs are obtained at 1-3-month intervals for 6 months.
 
Miscellaneous
Codes
ICD9-CM
728.89 Heterotopic ossification
 
Patient Teaching
  • Joint motion should be encouraged.
  • Immobilization is not recommended and can worsen the prognosis.
Activity
Patients are encouraged to use involved joints.
 
Prevention
Heterotopic ossification can be prevented in at-risk patients (e.g., trauma patients) with external beam irradiation or NSAIDs.
 
FAQ
Q: Which patients are at greatest risk for heterotopic ossification?
A: Patients who have substantial heterotopic ossification from a previous arthroplasty and patients who have AS (20-50% risk).
 
Q: Why are patients with a neurologic injury, such as head or spinal trauma, at such high risk?
A: Patients with a severe closed head injury or a spinal cord injury have a high risk of heterotopic ossification of the hip, shoulder, and elbow. Unfortunately, the cause of the heterotopic bone formation is unknown.

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