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Heterotopic ossification is frequently observed in the rehabilitation population. It consists of the formation of mature, lamellar bone in extraskeletal soft tissue where bone does not usually exist. Patient populations at risk of developing heterotopic ossification include patients with burns, strokes, spinal cord injuries, traumatic amputations, joint replacements, and traumatic brain injuries.
- Lesions range from small clinically insignificant foci of ossification to large deposits of bone that cause pain and restriction of function.
- The most common presentation is with pain around the ossification site.
What causes Heterotopic Ossification (HO)?
HO only occurs below the level of injury. The specific cause of HO after spinal cord injury is unknown. There are many theories about why it develops after spinal cord injury including:
- Trauma or injury
- Immobilization or paralysis
- Muscle spasms
- Loss of oxygen
- Severe bleeding
- Inflammation – the body’s natural response to injury
- Genetics
- Prolonged pressure on the hips
HO may develop within days following the spinal cord injury or several months later. HO usually occurs 3-12 weeks after spinal cord injury yet has been known to also develop years later.
HO occurs after other injuries, too. HO has been known to occur in cases of traumatic brain injury, stroke, poliomyelitis, myelodysplasia, carbon monoxide poisoning, spinal cord tumors, syringomyelia, tetanus, multiple sclerosis, post total hip replacements, post joint arthroplasty, and after severe burns.
In patients with spinal cord injury, 90% of cases occur in hips but it can also occur at the knees, elbows and shoulders. HO occurs more in men than in women. People in their 20’s and 30’s are affected more than other age groups.
Epidemiolgy
- HO 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 HO.
- The incidence of neurogenic HO is 10% to 20%.
- Following lower extremity amputation: 7%
- Following SCI: 20% (ranges reported from 20-40%)
- Following THA: 55%
- Following elbow fracture and/or dislocation: 90%
classification
Subtypes
- neurogenic HO (discussed here)
- traumatic myositis ossificans
- fibrodysplasia ossificans progressiva (Munchmeyer’s Disease)
- Presentation
- Imaging
- Radiographs
- recommended views
- Judet view valuable for evaluation of hip HO
- findings
- 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
- recommended views
- Ultrasound
- CT
- Triphasic bone scan
- Radiographs
- 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
- elevated serum alkaline phosphatase (>250IU/L)
- Histology
- mature fatty bone marrow
- mature trabecular bone
- Labs
Differential Diagnoses
The initial inflammatory phase of HO may mimic other pathologies such as cellulitis, thrombophlebitis, osteomyelitis, or a tumorous process.
Other differential diagnoses include DVT, septic arthritis, hematoma, or fracture. DVT and HO 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.
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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
- Quadriplegia and paraplegia
Preventative Measures
Because the cause of HO is currently unknown, preventive measures are limited. Some doctors will prescribe medications to prevent bone growth. The blood thinner Coumadin (Warfarin) is sometimes prescribed because it decreases the activity of Vitamin K, an important component in the development of bone. Another type of medication often prescribed is non-steroidal anti-inflammatory (NSAIDS) drugs. These medications prevent formation of bone growth by blocking prostaglandin cells from forming bone. Depending on your individual health and needs, your doctor and team will develop a plan that is right for you. All medications come with side effects – never start or stop a medication without consulting with your doctor first.
The Take-Home Message
People with SCI need to be aware of changes in sensation, function, pain and strength. With any change, speak with your doctor and report changes early. Losing function, movement or having pain can indicate problems like HO. Be proactive in your health and talk with your doctor about any changes you experience.
Treatment
Current treatment recommendations consist of mobilization with 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 orthopedic 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 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:
- Non-steroidal anti-inflammatory drugs: NSAIDS
Indomethacin (two-fold action)
1. Inhibition of the differentiation of mesenchymal cells into osteogenic cells (direct)
2. Inhibition of post-traumatic bone remodeling by suppression of prostaglandin-mediated response (indirect) and anti-inflammatory properties - Biphosphonates:
Three-fold action
1. Inhibition of calcium phosphate precipitation
2. Slowing of hydroxyapatite crystal aggregation
3. Inhibition of the transformation of calcium phosphate to hydroxyapatite.
Surgical interventions
The two main goals of surgical intervention are to
- Alter the position of the affected joint
- 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 HO present itself through decreased function and mobility, peripheral nerve entrapment, and pressure ulcers.
- Up to 70% of cases involving HA are asymptomatic.
- Ankylosis, vascular compression, and lymphedema can also be complications manifested in HO.
- 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 MO, usually athletes are able to progress to light activity at 2 to 3 months, full activity by 6 months, and back to their preinjury level by 1 year.
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Physical Therapy Management
Physical therapy has been shown to benefit patients suffering from heterotopic ossification. Pre-operative PT can be used to help preseve 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, hemorrhage, 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) Heterotopic ossification of the elbow
Goals:
- Prevent infection
- Protect and decrease stress on surgical site
- Decrease pain
- Control and decrease edema
- ROM to 80% of affected joint
- Maintain ROM of joint proximal and distal to surgical site
Phase II(2-8 weeks)
Goals:
- Reduce pain
- Manage edema
- Encourage limited ADL performances
- Promote scar mobility and proper remodeling
- Promote full ROM of affected joint
- Encourage quality muscle contractions Photo courtesy of prosportscare.com
Phase III (9-24 weeks)
Goals:
- Self-manage pain
- Prevent flare-up with functional activities
- Improve strength
- Improve ROM (if still limited)
- Return to previous levels of activity
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