Spasticity is an unmasked reflex that occurs when there is a lesion in the central nervous system (CNS) , a type of upper motor neuron (UMN) sign, first described by nineteenth century neurologist Hughlings Jackson [1]. Clinicians identify it as a velocity dependent increase in muscle tone when a particular muscle is stretched through its full range of motion. It can also be described as “muscle over activity.” Injuries to the CNS that can lead to spasticity include stroke, brain injury, spinal cord injury (SCI) , multiple sclerosis (MS) , and cerebral palsy . Prevalence varies from each condition: 28–38% in stroke patients, 60–80% in SCI patients, 41–66% in MS patients, and 13% in traumatic brain injury patients [2].

Spasticity is mediated through monosynaptic and polysynaptic spinal reflexes that are unmasked after injury to the CNS. There is reduced cortical inhibition of UMN spinal reflexes, which leads to a decreased threshold for reflex firing, and subsequent emergence of spasticity [3]. Spasticity emerges in SCI patients after spinal shock resolves.

There are characteristic spasticity patterns that can emerge in the upper and lower extremities. Upper extremities often will present with a flexor synergy pattern of finger flexion, wrist flexion, forearm supination or pronation, elbow flexion, and shoulder internal rotation [4]. The lower extremities often will present with an extensor synergy pattern of plantar flexion, toe flexion, knee extension, and hip extension [4]. Spasticity may also present with abnormal posturing of the trunk. Spasticity can often be made worse when the body perceives a noxious stimulus, such as bladder retention, urinary tract infection, pressure sore, ingrown toenail, constipation, occult fracture, excessively tight clothing, pulmonary embolus, or any other illness (e.g., syringomyelia).

Not all spasticity needs to be treated, and some spasticity may create a functional advantage that helps with gait mechanics, bed mobility, transfers, and general maintenance of muscle bulk. In other instances, spasticity is often associated with pain and discomfort when affected limbs are moved or stretched against the increased tone.

Many functional limitations can occur with both upper and lower extremity spasticity. Upper extremity spasticity can lead to an impaired ability to perform self-care, hygiene, grooming, feeding, and dressing. Lower extremity spasticity can impact gait, thereby increasing risk of falls and/or inability to tolerate braces.

Skin breakdown can occur in areas with joint tightness, which can limit the ability to maintain hygiene, such as cleaning the hands, genitals, or axilla. Skin breakdown can also occur with abnormal pressures across exposed joints.

Spasticity can also affect impact bladder and bowel management, as well as sexual activity.

Poor posture due to increased spasticity through the trunk can affect transfers, bed mobility, sleep, hygiene, and positioning while in the seated or supine position.

Spasticity, when sustained for an extended period of time, can lead to muscle and tendon shortening, ultimately leading to a functional state of contracture formation.