Spinal muscular atrophy (SMA) is caused by a mutation of the survival motor neuron 1 (SMN1) gene. Depending on the SMA type, the condition can lead to a variety of signs and symptoms, including scoliosis, difficulties with eating or breathing, joint contractures (arthrogryposis), muscle weakness (hypotonia), and reduced motor function. Bone fractures are also symptoms of SMA. This article will explore why SMA can cause bone fractures, as well as how to prevent and treat them.

What Causes Bone Fractures in SMA?

Bone health is an important consideration for people living with SMA, despite it being a neuromuscular condition (one that affects the nerves and muscles). SMA directly affects the nerve cells of the spinal cord that send signals to the muscles, particularly those that are proximal (in the center of the body) and in the legs. These muscles are also very important to maintaining bone strength. Muscle weakness, then, puts people with SMA at risk for bone fractures.

One study that assessed children with SMA type 2 or SMA type 3 who experienced bone fractures (as determined by X-ray scans) found that half of the kids had significantly reduced bone mineral density. Nearly 40 percent of the children had low levels of vitamin D (a nutrient that’s important in bone health). Additionally, 60 percent had high levels of C-terminal telopeptide, which indicates bone resorption, or breakdown. These factors can increase the risk of fractures, especially during falls.

Who’s at Risk?

People with any type of SMA can be at risk for decreased bone health and fractures — although people with intermediate forms of SMA, such as type 2 and type 3a, may experience fractures more often. Adults with the least severe forms of SMA (type 3b and type 4) are at less risk for bone fractures. Conversely, children with the most severe form of SMA (type 1, also known as infantile spinal muscular atrophy or Werdnig-Hoffmann disease) may not experience fractures as often. More often, they are treated for issues related to muscles that are involved in breathing and swallowing.

The age of first incidence (appearance of the condition) for SMA types 2 and 3a tends to be around age 9. However, fractures can occur at any age. Overall, the risk for osteopenia (bone mass degeneration), osteoporosis (bone disease), and fractures is high for all people who are living with SMA, regardless of age or SMA type.

Types of Bone Fractures in SMA

Most bone fractures in people with SMA are spontaneous and can occur with minimal movement or joint stress. These injuries are most common in the long bones of the body, such as the femur.

Congenital Bone Fractures

Congenital fractures are those that occur in a child before they are born. Congenital bone fractures are most common in children with SMA type 1.

Femur and Ankle Fractures

These distal (farther from the center of the body) fractures are most often noted in people with SMA type 2 or 3. The femur and ankle fractures can begin at an earlier age in people with SMA type 2 compared to those who have SMA type 3.

Upper Extremity and Facial Fractures

Fractures of the facial region (such as the nose) and upper extremities (such as the arms) are noted most often in people with SMA type 3. These people are less likely to experience limb fractures because they do not experience muscle weakness as early as people with SMA type 2.

Diagnosing Bone Fractures

Doctors may use imaging techniques to help see fractured bones and make a diagnosis. X-rays are used to produce an image of the bone in order to determine if a break or fracture has occurred following injury. These images can also help the doctor determine if they can reposition the bone break to help appropriate healing. Radiographs (X-rays) can also show bone demineralization in the legs of people with SMA who can no longer walk or who are experiencing bone degeneration due to reduced activity of the leg muscles.

Treating Bone Fractures in SMA

Ultimately, the treatment type can depend on the type of SMA that a person has, as well as their age at the time of injury. Fractures associated with SMA can heal fairly quickly. Limb immobilization, such as with a cast, should be limited to the shortest period of time possible so that the person with SMA can retain muscle strength in the area. Some femur fractures can be immobilized for as little as four to six weeks.

Radiographic testing can help the doctor determine how long a limb should be immobilized. Then, the doctor may recommend treatments for strengthening limbs and preventing future fractures.

Preventing Bone Fractures in People With SMA

Your doctor can recommend several options that can help prevent bone fractures in SMA, including physical therapy, dietary changes, and medications that target SMA directly.

Physical Therapy

Many people with all forms of SMA have treatment plans that involve physical therapy or occupational therapy. These sessions typically work to increase muscle strength of the legs, back, or facial muscles. An occupational therapist can teach people with SMA methods to conserve energy throughout the day. Conserving energy can extend the ability to perform daily activities such as walking safely, which may make falls less likely. A physical therapist can also help with techniques in fall prevention.

One mySMAteam member shared, “When I broke my femur, I did aquatic physical therapy. I loved it. I wish that I could still be doing it, but it is hard to find a pool that is close in order to put it into a daily routine.”

Another member described their experience recovering from a bad fall resulting in a fractured patella and hip. “After a week, I was transferred to the rehab center at the hospital where I received two to three hours of occupational therapy and physical therapy combined for six days a week,” they said. “I was sent home wearing a leg immobilizer and was using a walker to get around. I got physical therapy at home for about three months and was almost back to my previous levels of normal.”

Diet

Nutritional supplements such as calcium and vitamin D have been shown to help prevent loss of bone density in children with SMA. An appropriate diet can be a very beneficial tool in the prevention of bone deterioration for people living with SMA.

Medications

Bisphosphonates, drugs that slow bone loss, are also used in people with decreased bone density. Doctors may also prescribe treatment for SMA itself. Three disease-modifying drugs approved by the U.S. Food and Drug Administration (FDA) for the treatment of SMA are currently available.

Spinraza (nusinersen) was the first drug released in 2016 and is approved for people who are at least 2 years of age. Spinraza is given as an intrathecal injection (into the spinal canal).

In 2019, a new injectable drug called Zolgensma (onasemnogene abeparvovec-xioi) was approved as an intravenous drug and is a one-time injection that can be given to children younger than 2 years.

The most recently FDA-approved drug for SMA is Evrysdi (risdiplam), which is given as an oral liquid and does not require a hospital visit to be administered.

All of these drugs work to prevent or repair the damage to the muscle and spinal nerve cells in people with SMA. With greater muscle strength, bone support is increased and the risk for bone fractures can decrease. As one member shared, “At the time of my fall, I had been getting Spinraza for a year. I believe it helped me get most of the strength that I lost back.”

Talk To Others Who Understand

While everyone has different experiences, mySMAteam seeks to bring together people who are affected by SMA. On mySMAteam, a community of people living with or caring for someone with SMA comes together to ask questions, give advice, and share their experiences.

Have you experienced fractures with SMA? Share your experience in the comments below or start a conversation on mySMAteam.