Complications of Spinal Muscular Atrophy: Joint Contractures

People with spinal muscular atrophy (SMA) can develop long-term complications because of progressive muscle weakness. One complication that is especially common in Type 2 SMA is joint contractures. Contractures happen when joints become permanently shortened and stiff.1

Contractures can limit mobility and be very painful. Physical therapy focused on maintaining range of motion is a priority in managing SMA. Stretching exercises and bracing can help prevent or delay contractures. However, for many people with SMA, joint contractures are impossible to prevent.1

What are joint contractures?

Contractures are permanent shortening and stiffening of muscles or joints. They develop when normally flexible muscles or tendons get replaced by more rigid tissues. This causes the tissues to shorten and harden, leading to total loss of movement. Contractures can cause:1

  • Decreased motor function
  • Limited mobility
  • Reduced range of motion
  • Difficulty with daily activities
  • Increased pain

Why does SMA cause joint contractures?

Many factors combine to cause joint contractures. The most common cause is an inability to move joints because of muscle weakness. In other words, joints become “static” because they are not being used. Many people develop contractures after transitioning to a wheelchair. People who spend most of their time sitting with bent knees have a high risk for knee contractures. About half of people with type 2 SMA have a low range of motion at the knees.1,2

Another common cause of contractures in SMA is imbalanced muscle strength. When movement is dominated by one muscle group over another, range of motion can become reduced. For example, uneven strength of ankle muscles that move the foot downward and upward can lead to foot deformities.1,3

Joint contractures most often occur at the:4-6

  • Shoulders
  • Knees
  • Elbows
  • Hips
  • Wrists
  • Ankles

Decreased range of motion often develops at an early age and progresses. People with type 3 SMA or those who can walk have less risk of contractures. This is because their joints are not static and they have stronger muscles.4-6

What are symptoms of joint contractures?

Contractures are usually easy to notice and diagnose. The most common symptoms of a joint contracture are loss of movement and pain around the affected joint. Talk to your doctor if you think you or your child have a joint contracture. They will ask you about your symptoms and may perform imaging tests to diagnose the contracture.7,8

How are joint contractures prevented and treated?

Contractures impair mobility and can be painful. Prevention of contractures and slowing progression are priorities and should begin as soon as possible. Braces (orthoses) can be used to maintain range of motion. Stretching and exercise are also beneficial.4,6,8

What exercises to perform and how often to perform them depends on the highest motor milestone achieved. For example:3

  • People with SMA who cannot sit (type 1) should perform range-of-motion exercises 3 to 5 times per week.
  • People with SMA who cannot walk (type 2) should perform standing exercises for 60 minutes every day.
  • People with SMA who can walk (type 3 and 4) should maintain range of motion with 30 minutes of aerobic exercise every day.

However, even with proper management, contractures may be impossible to prevent for some people with SMA. If contractures remain painful and severely impair function, doctors may perform surgery. Lower limb contractures require surgery more often than upper limb contractures.3

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Written by: Matt Zajac | Last reviewed: August 2021