Peroneal spring

A peroneal spring is a splint (orthosis) that ensures the foot does not drop downward. People who, due to a nerve or muscle disorder, can no longer properly lift the foot benefit from such a splint. The peroneal spring is also called an ankle-foot orthosis.

What does a peroneal spring do?

A peroneal spring supports the foot while walking. It is a splint made of lightweight plastic. It runs along the back of the lower leg and under the sole of the foot. The peroneal spring is fastened to the lower leg and the foot with Velcro. Because the splint goes into the shoe, it is important that there is enough room in the shoe. Usually, removing the insole is sufficient.

The splint ensures that the foot remains at a 90-degree angle relative to the lower leg. But the peroneal spring is also a bit flexible. As a result, it supports the foot on the one hand when lifting it. On the other hand, the foot is able to move a little downward, which makes walking and cycling easier.

Who is a peroneal spring suitable for?

The peroneal spring is intended for people in whom the dorsiflexors do not work properly. The dorsiflexors are the muscles in the lower leg and foot that ensure that the foot and toes can be pulled up toward the lower leg. The most important dorsiflexor is the tibialis anterior muscle.

Without action of these dorsiflexors, the foot and the toes hang down. This is bothersome when walking. If the foot cannot be lifted, the whole leg has to be lifted higher to avoid tripping. This is called a steppage gait. With every step, the foot then ‘slaps’ on the ground, because the muscle strength to put it down gently is lacking. This is called foot drop.

If it is not possible to lift the whole leg high enough, the toes drag over the ground. The risk of falling is greater as a result. When a foot constantly hangs down, an equinus deformity can develop over time.

Causes of failure of the dorsiflexors

There are different causes for which the dorsiflexors no longer work properly:

• Nerve problem. The muscles that have to lift the foot are controlled by nerves. When there is a problem with the nerve, the muscles do not receive the signal to lift the foot properly. Examples include entrapment of a nerve such as with a herniated disc, injury to the peroneal nerve in the lower leg, a nerve disease such as MS, or brain injury.
• Muscle disease. There are different muscle diseases that cause muscle weakness or muscle failure. As a result, the dorsiflexors are not strong enough to lift the foot.
• Injury to muscles or tendons. Due to a muscle or tendon tear of the tibialis anterior muscle, the foot misses its most important dorsiflexor. The other muscles are not strong enough to lift the foot.

Not the solution to the problem

A peroneal spring provides support and protection for the foot. But wearing a splint does not, of course, solve the underlying problem. Therefore, it is important to also tackle the cause. For example, in the case of a trapped nerve, it has to be freed by a surgeon. If there is a muscle or tendon tear, then the physical therapist is the right person to help restore the strength and function of the dorsiflexors.