Heterotopic Ossification: Why Therapists Need to Know HO

Heterotopic Ossification can be confusing, misunderstood and underdiagnosed in sensitive patient populations including TBI, SCI and ortho. Learn why HO is not your average diagnosis and what you can do to protect your patients.

Why Therapists Need to Know Heterotopic Ossification

stretching to prevent heterotopic ossificationAbnormal bone growth in non-osseous tissues like muscle and other connective tissue?  It sounds like a sci-fi phenomenon that one would only encounter in a movie or on some dramatic medical television show.

In reality, heterotopic ossification (HO) occurs in 10-20% of patients with severe trauma and insults to the central nervous system (CNS), and 20% of people with severe brain injury.   That percentage can climb up to as high as 50% if there is severe brain injury and concomitant femur fracture.  Patients with brain injuries are at greater risk for developing heterotopic ossification if they have significant spasticity in the involved extremity, unconsciousness lasting longer than 2 weeks, long-bone or associated fractures, and decreased range of motion (ROM).

The risk of development of heterotopic ossification in a patient with brain injury increases as the severity of injury, length of immobilization, and duration of coma increase.  The incidence of HO. in military amputees related to conflicts in Iraq and Afghanistan has been found to be as high as 65%.  HO poses a threat to the integrity of wound healing, rehabilitation, and prosthetic fitting.

What Exactly is Heterotopic Ossification?

 HO is essentially bone growth in tissues like muscle and other connective tissues. Several terms have been used to describe the condition, including heterotopic ossification, ectopic ossification, and myositis ossificans .  HO is usually induced by fracture, burn, neurological damage including brain and spinal cord injuries and joint replacement.

Patients with HO experience swelling of tissues, inflammation, pain, limited motion and joint adhesion.  HO can be further specified into three categories:  myositis ossificans progressiva, myositis ossificans circumscripta without trauma (also known as neurogenic HO), and traumatic myositis ossificans.

Myositis ossificans progressive:  a rare metabolic bone disease present in children with progressive metamorphosis of skeletal muscle to bone
Myositis ossificans circumscripta without trauma:  also known as ‘neurologic heterotopic ossification’ localized soft tissue ossification occurring after neurologic injury or burns

Traumatic myositis ossificans:  occurs from direct injury to the muscle; fibrous, cartilaginous, and osseous tissue near the bone are affected and the muscle may not be involved.

For purposes of this article, we’ll be focusing on the latter two types of heterotopic ossification.

How is Heterotopic Ossification Diagnosed?

Not all people who experience trauma or severe brain injury are going to develop heterotopic ossification, however it is important as a clinician to know the signs and symptoms.  This will ensure early intervention for services rendered, preventing additional loss of function and interruption in therapeutic services. It is important to note that 75% of post-traumatic HO was diagnosed in the rehabilitation unit.

If you work in inpatient rehabilitation, you know that someone’s time there is both limited and precious–something like a missed heterotopic ossification diagnosis can completely derail your patient’s rehabilitation course.  Learn more about 14 Strategies to get your CVA patient home quicker!

The first signs and symptoms of heterotopic ossification are reduced joint ROM and painful ROM testing, swelling, erythema, and contracture formation.  In people with severe neurological impairment, other signs including autonomic dysfunction and local inflammation in addition to ROM should be considered.

Local pain and a palpable mass may be present one to three months post-injury, however in severe brain injury, HO may be present up to seven months post-injury.  Things like laboratory tests, radiology studies, and bone scans should be utilized to accurately confirm an HO diagnosis.

heterotopic ossification labs

Lab Tests:  Alkaline phosphates should be measured, as there has been shown to be a correlation between a rise in levels and level of ossification. There is also evidence supporting that when alkaline phosphate levels return to normal, ossification will have stopped.

Radiology:  X-rays will not show HO in the acute phase of inflammation when there is still active pain and swelling.   X-rays taken 4-5 weeks post injury will begin to show immature ossification and possibly mature bone growth.  It can take anywhere from 8-14 months for HO to reach full maturity, so repeat imaging may be in the patient’s best interest if HO is suspected.

Bone Scans:  Triple phase bone scanning has been the most effective diagnostic method for early detection of HO as it detects early increases in vascularity.  The first and second phases of the triple-phase bone scan show increased uptake. Areas demonstrating increased blood flow and soft-tissue concentration of the tracer on early imaging (blood flow phase) correlate with sites of subsequent HO development. The optimal timing of the imaging for accurate assessment of the presence of ectopic bone has not been established, but 3 weeks or more following the injury should be sufficient for early detection (Bruno-Petrina, 2021).

How is Heterotopic Ossification Treated?

Therapy’s role in the management of HO is challenging and somewhat ill defined.  The goal of HO management should be to maintain ROM in order not to lose any function.  The literature generally supports the common use of active ROM exercises and gentle, passive ROM exercises to maintain available joint motion and to avoid progressive contractures.

There has been no evidence found for increased HO or decreased ROM with passive ROM exercises.  Surgical intervention can also take place to remove the abnormal bone growth if it is severely impairing functional mobility, but it is recommended that take place approximately 18 months post injury.

Can Heterotopic Ossification be Prevented?

learning about heterotopic ossification

The short answer is possibly.  (Per Sun in 2021) Prevention involves identifying patients with high risk of developing HO. It is important to note that routine prevention on all patients is not recommended. Current recommendations for prevention of HO are gentle ROM exercises, pharmacologic agents (indomethacin and etidronat), and external beam radiation (which is primarily used after joint arthroplasty).

Management of risk factors, such as spasticity, is also incredibly important. NSAIDS are thought to reduce the inflammation around joints which could prevent the development of HO.  Indomethacin is the most commonly used NSAID for prophylaxis, with other effective NSAIDS being meloxicam, celecoxib, rofecoxib, and ibuprofen. Etidronate is a bisphosphonate–a type of drug that slows bone loss–that has been approved for prevention of HO in spinal cord injuries and complications of total hip arthroplasty.

How Can I Improve my care for Patients with Heterotopic Ossification?

Be well informed--especially if your setting has patients who are at risk of developing HO–it puts you one step ahead if you are up to speed with the potential complications that can occur with a particular patient population.  Seeking out meaningful continuing education and collaborating with the interdisciplinary care team is a great way to stay on top of the most recent developments in HO treatment.

If you feel a patient is meeting the criteria for development of HO or is beginning to display early symptoms, speak up!  Speak with the physician regarding your concerns and ensure you bring the data with you to validate your claims.  It cannot be stressed enough that the best treatment for HO is prevention–prevention of the abnormal bone growth as well as prevention of  any further physical complications if the bone growth occurs.  Advocate for your patients, and educate your fellow staff members & fight back against HO.

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