The flexor synergy pattern is an involuntary, coupled movement of the arm or leg that frequently emerges following a stroke. This pattern involves the simultaneous contraction of multiple muscle groups, preventing the person from moving a single joint in isolation. This mass movement is a common motor impairment, signaling the brain’s initial attempts to re-establish communication with the affected limb after injury.
The Neurological Cause of Synergy
The origin of the flexor synergy lies in the damage inflicted upon the central nervous system by the stroke, specifically affecting the corticospinal pathways. These pathways, which make up the pyramidal tract, are responsible for sending precise signals from the motor cortex to the spinal cord, enabling fine, isolated joint movements. When these tracts are damaged, the brain loses its ability to exert inhibitory control over lower motor centers.
This loss of inhibitory control allows more primitive brainstem pathways, particularly the reticulospinal tract, to become dominant. This tract activates large groups of muscles simultaneously rather than controlling individual ones. Consequently, any attempt to initiate movement results in the simultaneous firing of these coupled muscle groups, leading to the obligatory flexor synergy pattern. The brain reverts to a basic motor program because the fine-control system has been compromised.
Recognizing the Specific Movement Pattern
The visual presentation of the flexor synergy is a recognizable posture, particularly in the upper extremity. When a person attempts to move their arm, the pattern typically involves the shoulder pulling back and elevating, with the upper arm turning outward and moving away from the body. The elbow then bends, often becoming the strongest component of the entire synergy.
This movement is coupled with the forearm rotating (supination) so the palm faces upward. Simultaneously, the wrist and fingers curl into a flexed position, sometimes resulting in a clenched fist. This coupled action makes it difficult to perform tasks requiring reaching, elbow extension, or hand opening, as all joints move together.
While the upper extremity pattern is the most common, a similar synergy can affect the lower extremity. The leg flexor synergy involves the hip flexing, pulling the knee upward toward the abdomen, and rotating the leg outward. This action combines with the knee bending and the ankle moving into dorsiflexion (foot pulled upward toward the shin). This pattern is often seen during the swing phase of walking to lift the foot off the ground.
Therapeutic Strategies for Improvement
Rehabilitation for flexor synergy focuses on retraining the brain to move individual joints outside of the mass pattern through a process called neuroplasticity. Therapists guide individuals to practice isolated joint movements, which directly opposes the coupled action of the synergy. Repetitive, meaningful practice of these independent movements helps establish new, functional neural pathways in the brain.
Several strategies are used to break the pattern. A primary goal is to promote weight-bearing through the affected limb, which helps normalize muscle tone and facilitate joint alignment. Functional task training is also incorporated, requiring the person to use the affected limb in daily activities to encourage extension and break the dominant flexor pattern. Stretching and proper positioning are performed to prevent contracture, a complication where muscles become permanently shortened.
In some cases, medical management is used as an adjunct to physical therapy, primarily involving targeted injections of neurotoxins, such as botulinum toxin (Botox). These injections temporarily relax the strongest flexor muscles, reducing the intensity of the synergy. By dampening the muscle activity, the injections create a therapeutic window that allows the patient to practice isolated movements more effectively and gain a greater range of motion.