When a stroke occurs, part of the brain is injured or irreparably damaged. Because the parts of the brain that control the shoulder and initiate movement to that joint may be affected, this can change the tension of the shoulder. The tone, or tension, of the shoulder can either be reduced causing a subluxation, which is a dislocation of the shoulder, or the tone can be increased, creating spasticity and limiting movement. However, the brain and limb can often be rehabilitated, decreasing the effects of the stroke on the shoulder.
Subluxation: a gravity-assisted dislocation
Often, the shoulder demonstrates reduced tension, especially in the first two months following a stroke. When there is a significant reduction in tone, known as hypotonicity, the shoulder can actually dislocate. An anterior subluxation can occur when the top of the humerus, the bone in the upper arm, pushes toward the front of the body. A distal subluxation occurs when the shoulder dislocates downward, away from the shoulder joint. Although both subluxations can contribute to permanent injury and pain because the dislocated end of the bone can tear muscles, nerves, ligaments, or tendons, distal subluxation has the greatest risk for secondary injury. These dislocations occur because the damaged brain is no longer sending signals to the shoulder muscles to contract and move and because unused muscles atrophy; the weakened muscles can no longer hold the bone in place.
Treaments used for shoulder subluxation
Your doctor will likely recommend therapy for your subluxed shoulder, often completed by either a physical therapist or occupational therapist. If your subluxation is significant, which is often the case during the first month or so following a stroke, your therapist may recommend a subluxation sling. This sling will fit over the shoulder joint, similar to a short sleeve of a shirt, and wrap around the chest. The purpose of the subluxation sling is to help keep the humerus in the shoulder socket, thus reducing the risk of injury to the shoulder soft tissues. Also, you may have electrical stimulation in therapy. Often therapists will use weight-bearing activities to increase your brain's awareness of the shoulder to help strengthen the shoulder and increase spontaneous nerve stimulation from the brain.
Spasticity in the shoulder muscles
The opposite symptom may be experienced after a stroke, wherein the shoulder muscles are stimulated incorrectly, thus increasing the tone of the shoulder muscle group. Often, as the brain rehabilitates, it begins to send signals to the shoulder muscles via the nerves, but the signals are inappropriate and imbalanced. This effectively causes the muscles on both sides of the shoulder to contract at the same time, creating spasticity and often severely limiting shoulder movement. This can occur after a period of subluxation, during the rehabilitation process, but may not completely resolve in all cases.
Treatments used for shoulder spasticity
Your therapist may use multiple approaches to address your shoulder spasticity. Range of motion, either active or passive, will likely be a part of your rehabilitation. Furthermore, a specialized form of range of motion, referred to as "Bobath inhibition" or "PNF diagonals," may help to reduce your spasticity. These exercises must be done by a trained therapist to achieve the maximum results. These specialized exercises combine all aspects your arm's range of motion to help to break the cycle of improper stimulation from your brain to your muscles. For very severe or painful spasticity, your therapist may attempt deep tendon pressure to disengage the muscle's effect on the joint, allowing for increased range of motion.
Modalities for shoulder tension changes following a stroke
Several modalities may be used as a complement to your therapy. One is neuromuscular electrical stimulation. Unlike traditional electrical stimulation, this modality sends signals to opposite muscle sets in patterns that closely simulate normal brain signalling. This helps to strengthen your muscles, reduce tone by reminding the brain how it should send signals, and rehabilitate the brain by stimulating its awareness of your shoulder. Also, to help control pain, your therapist may utilize moist heat to relax the muscles in a spastic shoulder. Additionally, a vibrating massager may be used over weak muscle fibers to stimulate contractions.
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