Exploring Spasticity

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About Spasticity
Spasticity is defined as an involuntary, velocity-dependent, increased resistance to stretch. This definition means that the amount of resistance to stretching is at least partly determined by the speed with which a spastic muscle is stretched. One factor that is thought to be related to spasticity is the stretch reflex. This reflex is important in coordinating normal movements in which muscles are contracted and relaxed and in keeping the muscle from stretching too far.

Although the end result of spasticity is problems with the muscles, spasticity is actually caused by an injury to a part of the central nervous system (the brain or spinal cord) that controls voluntary movements. The damage causes a change in the balance of signals between the nervous system and the muscles. This imbalance leads to increased activity (excitability) in the muscles.

What is Normal Muscle Control?

Overview of Muscles
To better understand what happens in muscles that are affected by spasticity, it is helpful to first understand some key facts about muscles and the nerves that control their movements.

· More than 600 muscles, along with the bones, make up the musculoskeletal system.
o The bones provide the structure or support for the body, and the muscles provide the ability to move.
o Muscles are connected to bones by tough cords of tissue called tendons.
o Most muscles reach from one bone to another and usually cross a joint.
o The muscles cause the bones to move in relationship to each other.
· Most muscles of the musculoskeletal system work in pairs—called agonists and antagonists.

During a movement, the muscle responsible for moving the body part contracts or shortens; this muscle is called the agonist. The antagonist muscle acts against or in opposition to the agonist muscle, stretching when the agonist contracts. The antagonist muscle is responsible for moving the body part back to its original position.

A muscle acts as the agonist in one action and as an antagonist in the opposite action. For example, when bending the elbow and raising the hand toward the shoulder, the bicep muscle contracts and is the agonist; the tricep muscle stretches and is the antagonist. When the movement is reversed and the elbow is extended, the tricep muscle contracts (is the agonist) and the bicep muscle lengthens (is the antagonist).

Overview of Spasticity
The most common causes of spasticity are lack of oxygen to the brain before, during, or after birth (cerebral palsy); physical trauma (brain or spinal cord injury); blockage of or bleeding from a blood vessel in the brain (stroke), and multiple sclerosis (MS). When the damage that causes the eventual spasticity first occurs, the muscles are usually flaccid before they become spastic.

Spasticity may not be present all the time—it may be related to a trigger, or stimulus, such as pain, pressure sores, a urinary tract infection, ingrown toenails, tight clothing, or constipation.

Spasticity may be painful, especially if it pulls joints into abnormal positions and or prevents a normal movement of the joints. In some patients, spasticity may cause slight muscle stiffness; in others, there is permanent shortening of the muscle. When the muscle is permanently shortened, the joint becomes misshapen. This is called a contracture and is one of the most significant consequences of spasticity. Another closely related problem with muscles in many people who have spasticity is clonus, or rapid, repeated muscle spasms.

While spasticity may affect any muscle group, there are some common patterns. When spasticity affects one or both arms, flexed (bent) elbow, flexed wrist, and clenched fist may result. These can all affect the person’s ability to dress, eat, or write or may interfere with balance, thereby causing difficulties with walking. Spasticity of the legs can cause flexed hip, adducted (or scissoring) thigh, stiff knee, flexed knee, equinovarus foot, and hyperextended great toe (which is also called the hitchhiker’s toe). Spasticity of one or both legs may interfere with the ability to walk, position in bed, sit, transfer, or stand. In this way, spasticity can make daily care more difficult. Spasticity may be limited to one area (localized), several nearby areas (regional), or many muscles or muscle groups of the body (generalized). When spasticity is generalized daily care may be challenging and lack of comfort becomes an important consideration for treatment approaches.

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