Understanding spasticity

Spasticity is an involuntary increase in muscle tone after damage to the brain or spinal cord: the muscle resists being stretched. It can be useful — some people stand on spastic tone — so the goal is not to remove it but to convert it into usable function.

Damage to the descending pathways removes some of the normal inhibition on spinal reflexes. The reflexes become overactive, and the muscle responds to stretch with contraction rather than allowing the movement.

Spasticity is velocity-dependent — it appears when a muscle is stretched quickly and may be absent when the same joint is moved slowly. This is why an examiner moves a limb at different speeds, and why a measurement taken by one clinician does not always match another's.

Treat it when it causes pain, interferes with positioning or care, or blocks a movement the person could otherwise make. Leave it when it is providing useful stiffness — reducing tone in a leg that someone is standing on can cost them standing.

Before treating, it is worth checking for a trigger. A urinary infection, constipation, a pressure sore, an ingrown toenail or a tight shoe can all raise tone substantially, and in spinal cord injury a sudden increase in spasticity is a recognised warning sign that something else is wrong.

Positioning and stretching first, robotic or guided movement to maintain range, splinting where indicated, and injection therapy for focal problems. Every tone measurement is reported alongside a function measurement so that a loss of useful tone is visible.

Botulinum toxin injection creates a window of reduced tone lasting around three months 2. That window is only useful if stretching, splinting and functional training happen inside it — injection without a therapy plan attached buys three months 2 and changes nothing.

Spasticity is an active, velocity-dependent muscle contraction driven by the nervous system. Contracture is a fixed shortening of muscle and connective tissue that persists even under anaesthesia. Untreated spasticity leads to contracture, but they are different problems needing different treatment.

The practical distinction: spasticity responds to tone-reducing treatment, contracture does not. A limb that will not straighten under sedation has a contracture, and injection will not change it.