Spasticity may affect any muscle or group of muscles, but common patterns are often seen. Each causes its own set of impairments. For instance, the forearm may be drawn up and in toward the chest, making it difficult to put on or take off a shirt. The thighs may be pulled close together, not only making dressing difficult, but narrowing the base of support for standing and walking. The fingers may be clenched tight, driving the nails into the palm and preventing access for cleaning, resulting in infections and skin breakdown. One of the most common patterns is termed equinus, in which the calf muscles tighten, preventing the ankle from flexing completely and leading to walking on the toes.
When the muscle that is overactive is also very strong, it can lead to more severe complications, including partial dislocation. Hip dislocation is a common complication of spasticity in cerebral palsy. A constant imbalance in the forces across a joint due to spasticity can cause the bone to form new tissue in response, leading to bony deformities.
Inactivity brought on by disability can lead to a host of other problems, including pressure sores, osteoporosis, respiratory infections, and social isolation.
The resistance to stretch that characterizes spasticity may be mild and infrequent, or it may be severe and quite frequent. In the latter case, the patient can rarely attain a fully stretched position for the muscle, and the muscle spends more time than normal in a partially shortened position. When this occurs, a muscle can develop contracture. A contracture is the loss of full range of motion of a joint due to changes in the soft tissues (muscles and tendons) surrounding that joint. In contracture, the muscle fibers remodel themselves to accommodate this shorter length, thus shortening the muscle overall. In addition, the muscle may develop more fibrous tissue that cannot stretch as much, further increasing its resistance to stretch.
A muscle that develops contracture becomes almost impossible to stretch out to its full length, further worsening the clinical problems of the person with spasticity.
Richard Robinson, The Gale Group Inc., Gale, Detroit,