Complications of Spinal Muscular Atrophy: Fractures

Reviewed by: HU Medical Review Board | Last reviewed: August 2021

People with spinal muscular atrophy (SMA) have muscle weakness because of a defect in their motor neurons. In severe types of SMA, weakness can progress and cause serious complications. One common complication of SMA is bone fractures.

Fractures are broken bones often caused by sudden impact. People with SMA often have weaker bones, which can increase the risk for fractures. People with SMA should be monitored regularly for bone health. Physical therapy and nutritional support can help improve bone health. Treatment usually includes casts or surgery.

What are bone fractures?

Bone fractures are also called broken bones. They are very common and often caused by sports injuries, car accidents, or falls. Certain conditions that weaken bones may increase the risk of fractures. Fractures are often called “fragility fractures” when bone weakness contributes to the injury.1

There are many types of fractures. Fractures can be open or closed, depending on whether the injury breaks through the skin. Fractures can also be complete or partial, depending on whether the break goes all the way through the bone.1

Why does spinal muscular atrophy cause fractures?

People with SMA have a genetic defect that causes a lack of “survival of motor neuron” (SMN) protein. This causes motor neurons to die, leading to weakness of certain muscles. Poor bone health is also common in SMA. About half of people with SMA have low bone density. This is likely due to:2-5

  • Lack of movement and exercise
  • Muscle weakness
  • Poor nutrition, especially vitamin D and calcium deficiency

Low bone mass may also be caused by SMA itself. Some research shows that the survival of motor neuron (SMN) protein is directly involved in bone maintenance and repair.6,7

Low bone density increases the risk of fractures for people with SMA. A 2017 study found that 38 percent of people with SMA types 1, 2, or 3 who lived longer than 1 year had experienced fractures. The most commonly fractured bone in SMA is the thigh bone (femur). Fractures are commonly caused by falls. However, spontaneous fractures may also occur in people with SMA. These are fractures in seemingly normal bone with no obvious blunt-force trauma.8,9

What are the symptoms?

Symptoms of fractures depend on the bone that breaks. Usually, fractures are immediately noticeable. Possible symptoms of a fracture include:1

  • Severe pain
  • Swelling
  • Unusual bump, bend, or twist
  • Difficulty using the limb

Doctors diagnose fractures with a visual exam and imaging tests. Possible imaging tests include X-rays or CT scans.

How are they prevented and treated?

Fractures should be prevented in SMA with different methods to improve bone health. This includes increasing intake of calcium and vitamin D. It also includes physical therapy and regular monitoring of bone density.2

It is also important to minimize fractures by reducing the chance of tripping or falling. Some tips to avoid falls include:1

  • Remove clutter and wires that cross walkways
  • Make sure rooms are well-lit
  • Use skid-free mats under rugs
  • Wear shoes (not just socks) indoors
  • Keep walkways free of ice and snow

Treatment usually depends on mobility. Closed cast immobilization may be used for people who cannot walk. However, long-term casting (longer than 4 weeks) can worsen muscle and bone mass loss. Experts may recommend surgical stabilization in some cases. This surgery uses rods or plates to stabilize the fractured bone. It can improve range of motion and speed up healing.2

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