Heterotopic Ossification

Original Editors - Bruce Tan as part of the from Bellarmine University's Pathophysiology of Complex Patient Problems project.

Top Contributors - Bruce Tan, Morgan Yoder, Hannah McCabe, Naomi O'Reilly, Lucinda hampton, Admin, Elaine Lonnemann, 127.0.0.1, Wendy Walker, WikiSysop and Kim Jackson

Introduction

Heterotopic ossification is seen often in rehabilitation population. It refers to the formation of mature, lamellar bone in extraskeletal soft tissue where bone should not be. Patients at risk of developing heterotopic ossification include patients with burns, strokes, spinal cord injuries (SCI), amputations, joint replacements, and traumatic brain injuries (TBI).

• Lesions range from small, clinically insignificant foci of ossification to large deposits of bone that cause pain and restriction.
• The most common presentation is with pain around the ossification site

Figure.1 CT Scan showing Heterotopic Ossification of Proximal Femur

Figure.2 Radiograph showing Heterotopic Ossification of the Hip

Etiology

The exact mechanism of heterotopic ossification (HO) in traumatic and neurogenic heterotopic ossification is unknown, but two common factors precede the formation of heterotopic ossification , the first being trauma or an inciting neurological event.

1. Traumatic (fracture, arthroplasty, muscular trauma, joint dislocation, burns). In total joint arthroplasty, heterotopic ossification most commonly occurs for the replacement of hips, knees, elbow, and shoulder. Chronic muscular trauma leads to what is traditionally known specifically as traumatic myositis ossificans. The most common sites for traumatic myositis ossificans are the quadriceps femoris muscle and the brachialis muscle.
2. Neurogenic (Stroke, SCI, TBI, Brain Tumors). The most common sites for neurogenic heterotopic ossification are the hips, elbows (extensor side), shoulders, and knees. Uncommon sites of heterotopic ossification that may be encountered in a rehabilitation setting are incisions, kidneys, uterus, corpora cavernosum, and the gastrointestinal tract. The exact cause and mechanism of neurogenic heterotopic ossification are unknown.

Risk Factors

• Spasticity, older age, pressure ulcer, the presence of deep vein thrombosis, having a tracheostomy, long bone fractures, prior injury to the same area, edema, immobility, long-term coma, and severity of injury (Trauma, TBI, SCI, Stroke).
• High/Moderate risk factors in the THA population include men with bilateral THA, prior history of heterotopic ossification, ankylosing spondylitis, diffuse idiopathic hyperostosis, or Paget's Disease.

Epidemiology

• Heterotopic Ossification is twice as common in males versus females, but it is noted that females older than 65 years old have an increased risk of developing heterotopic ossification.
• The incidence of neurogenic heterotopic ossification is 10% to 20%.
• Following lower extremity amputation: 7%
• Following SCI: 20% (ranges reported from 20-40%)
• Following THA (total hip arthroplasty): 55%
• Following Elbow Fracture and/or Dislocation: 90%
  

Signs and Symptoms

Figure.3 Heterotopic Ossification Progression of the Hip

Clinical signs and symptoms of heterotopic ossification may appear as soon as 3 weeks or up to 12 weeks after initial musculoskeletal trauma, spinal cord injury, or other precipitating events. The first sign of heterotopic ossification is generally loss of joint mobility and subsequently loss of function. Other findings that may suggest the presence of heterotopic ossification include swelling, erythema, heat, pain depending on sensory deficit, hard, palpable mass, pressure area, contracture formation and spasticity and autonomic dysreflexia in individuals with spinal cord injury. In some cases, a fever may be present. 

1. Symptoms: Painless Loss of ROM, Interferes with activities of daily living) ADL, Complex regional pain syndrome) CRPS, Fever
2. Inspection: Warm, Painful, Swollen Joint; may have effusion; Skin Problems (pressure ulcers from contractures around skin, muscles, ligaments, skin maceration and hygiene problems)
3. Movement: Decreased Joint ROM; Joint Ankylosis; with heterotopic ossification after total knee arthroplasty (TKA), might develop quadricep muscle snapping or patella instability
4. Neurovascular: Peripheral Neuropathy; heterotopic ossification often impinges on adjacent neurovascular structures

Differential Diagnoses

The initial inflammatory phase of heterotopic ossification may mimic other pathologies such as cellulitis, thrombophlebitis, osteomyelitis, or a tumorous process.

Other differential diagnoses include deep veinous thrombosis (DVT), Septic Arthritis, Haematoma, or Fracture. DVT and heterotopic ossification have been positively associated. This is thought to be due to the mass effect and local inflammation of the HO, encouraging thrombus formation. The thrombus formation is caused by venous compression and phlebitis.

Diagnosis

Diagnosis is made when soft tissue ossification with sharp demarcation from surrounding soft tissues is seen on radiograph. However, plain radiographs may not be able to detect early lesions, so ultrasonography is more commonly used as an early screening modality, despite magnetic resonance imaging remaining the gold standard for imaging of soft tissue masses.

Figure.4 CT Scan showing Heterotopic Ossification of the Shoulder

Figure.5 AP X-ray Showing Heterotopic Ossification of Shoulder

Associated Co-Morbidities

The most common conditions found in conjunction with heterotopic ossification:

• Ankylosing Spondylitis
• Rhuematoid Arthritis
• Hypertrophic Osteoarthritis
• Diffuse Idiopathic Skeletal Hyperostosis
• Paget's Disease
• Spinal Cord Injury
  

Treatment

Heterotopic Ossification is best managed by an interprofessional team. The condition is not only difficult to diagnose because of lack of specific markers but its treatment is not satisfactory. Current treatment recommendations consist of mobilisations with gentle ROM exercises, indomethacin, etidronate, and surgical resection.

• Early treatment with a passive range of motion exercises should be implemented once the presence of HO is confirmed to prevent ankylosing of joints.
• Absolute treatment consists of surgical resection of mature bone once the HO has fully matured. This can be 12 to 18 months after the initial presentation.
• Surgical consultation with an orthopaedic surgeon is warranted only if there will be an improvement in function as demonstrated by mobility, transfers, hygiene, and ADLs.
• Indomethacin and etidronate are also used to help arrest bone formation in HO, but efficacy in the traumatic brain injury population has not been clearly proven (see below).
• The most effective treatment option in the TBI population is surgical resection. In the SCI population, the most effective Non-Steroidal Anti-Inflammatory Drugs (NSAID) treatment regiments are either Rofecoxib 25 mg per day for 4 weeks or indomethacin 75 mg daily for 3 weeks.

Medications

The two types of medications shown to have both prophylactic and treatment benefits are as follows:

1. Non-Steroidal Anti-Inflammatory Drugs (NSAIDS)
   Indomethacin (two-fold action)
   • Inhibition of the differentiation of mesenchymal cells into osteogenic cells (direct)
   • Inhibition of post-traumatic bone remodelling by suppression of prostaglandin-mediated response (indirect) and anti-inflammatory properties
2. Biphosphonates: Three-fold action
   • Inhibition of calcium phosphate precipitation
   • Slowing of hydroxyapatite crystal aggregation
   • Inhibition of the transformation of calcium phosphate to hydroxyapatite.

Surgical Interventions

The two main goals of surgical intervention are to

1. Alter the position of the affected joint
2. Improve its range of motion (ROM).

Rehabilitation Post-Operatively: It is recommended that a rehabilitation program should start within the first 24 hours after surgery. The program should last for 3 weeks to prevent adhesion.

Prognosis

Complications of heterotopic ossification present itself through decreased function and mobility, peripheral nerve entrapment, and pressure ulcers.

1. Up to 70% of cases involving HA are asymptomatic.
2. Ankylosis, vascular compression, and lymphedema can also be complications manifested in HO.
3. Prognosis is generally good after surgery. Mean time from injury to surgery is 3.6 years. Once the surgery is performed, studies have shown that average ROM in the hip can improve from 24.3 to. After surgery, improvement was maintained in follow up 6 months after surgery. Complications from surgical resection of HO, such as infection, severe hematoma, and DVT

In the case of sporting myositis ossificans, usually athletes are able to progress to light activity at 2 to 3 months, full activity by 6 months, and back to their pre-injury level by 1 year.

Physical Therapy Management

Physical therapy has been shown to benefit patients suffering from heterotopic ossification. Pre-operative PT can be used to help preserve the structures around the lesion. ROM exercises (PROM, AAROM, AROM) and strengthening will help prevent muscle atrophy and preserve joint motion.

Clinical Note: Caution must be taken when working with patients with known heterotopic lesions. Therapy which is too aggressive can aggravate the condition and lead to inflammation, erythema, haemorrhage, and increased pain.

Post-operative rehabilitation has also shown to benefit patients with recent surgical resection of heterotopic ossification. The post-op management of HO is similar to pre-op treatment but much more emphasis is placed on edema control, scar management, and infection prevention. Calandruccio et al. outlined a rehabilitation protocol for patients who underwent surgical excision of heterotopic ossification of the elbow. The phases of rehab and goals for each phase are as follows:

Phase I (Week 1)

Elbow Heterotopic Ossification

Goals:

1. Prevent infection
2. Protect and decrease stress on surgical site
3. Decrease pain
4. Control and decrease edema
5. ROM to 80% of affected joint
6. Maintain ROM of joint proximal and distal to surgical site

Phase II (2-8 Weeks)

Goals:

1. Reduce ain
2. Manage Edema
3. Encourage limited ADL performances
4. Promote Scar Mobility and proper remodeling
5. Promote full ROM of affected joint
6. Encourage quality muscle contractions
   

   Photo courtesy of prosportscare.com

Phase III (9-24 Weeks)

Goals:

1. Self-manage Pain
2. Prevent flare-up with functional activities
3. Improve Strength
4. Improve ROM (if still limited)
5. Return to previous levels of activity