The extensor synergy pattern in the lower extremity is an involuntary, coordinated movement that can emerge after a neurological injury. This pattern involves a group of muscles working together in a fixed, often rigid, way, making it difficult to perform isolated or smooth movements. It represents a deviation from typical motor control, where individual muscles or smaller groups of muscles can be activated independently for varied actions. This pattern can impact daily activities and functional mobility.
Understanding Muscle Synergy Patterns
Muscle synergies are a fundamental way the brain organizes movement, allowing multiple muscles to work together efficiently to perform a specific task. In a healthy nervous system, these synergies are flexible, adapting to the demands of diverse movements, like walking or reaching. These synergies simplify complex motor control, ensuring precision and minimal energy waste.
However, damage to the brain or spinal cord can disrupt this intricate organization, leading to the emergence of abnormal, stereotyped synergy patterns. These abnormal synergies often occur when an individual attempts a voluntary movement. Unlike normal, adaptable synergies, these patterns are fixed, meaning that when one component of the pattern is activated, other components also activate involuntarily. This makes it challenging to move a single joint or muscle independently without triggering the entire pattern.
Specific Movements of Extensor Synergy
The extensor synergy pattern in the lower extremity involves a specific set of movements that occur simultaneously across the hip, knee, and ankle joints. At the hip, the pattern typically includes extension, where the leg moves backward, along with adduction, which pulls the leg inward towards the body’s midline, and internal rotation, causing the leg to twist inward.
Moving down to the knee, the extensor synergy pattern manifests as knee extension, meaning the leg straightens out. This straightening can make it difficult to bend the knee for activities like walking or sitting. Finally, at the ankle, the pattern involves plantarflexion, which is the pointing of the foot downwards, similar to pressing a gas pedal, and inversion, where the sole of the foot turns inward.
These movements occur together as a single, coordinated unit, making it challenging to perform isolated actions. For example, attempting to straighten the knee might involuntarily cause the foot to point downwards and inward. This coupled movement can significantly interfere with functional activities like standing and walking, as the foot pointing downwards makes it difficult to maintain balance.
Underlying Neurological Causes
Extensor synergy patterns in the lower extremity commonly develop following damage to the central nervous system. Stroke, or cerebrovascular accident, is a leading cause, where interruption of blood flow to the brain leads to neuronal damage. This damage can affect areas such as the motor cortex and descending pathways, which are responsible for voluntary movement and inhibiting abnormal reflexes.
Other neurological conditions, including traumatic brain injury (TBI) and spinal cord injury, can also result in these patterns. In these instances, the damage to the brain or spinal cord disrupts the normal communication between the brain and the muscles. The result is a loss of selective motor control, where the brain can no longer activate individual muscles or small groups of muscles independently. Instead, larger, less refined movement patterns, like the extensor synergy, emerge. Disinhibition or abnormal activation of certain neural pathways, such as the reticulospinal tracts, contributes to these movements.
Strategies for Management and Rehabilitation
Management and rehabilitation for the extensor synergy pattern focus on improving functional movement, reducing muscle overactivity, and enhancing overall quality of life. Physical therapy plays a key role, retraining the brain and promoting more normalized movement patterns. Therapists often employ neurodevelopmental treatment (NDT) to facilitate normal movement and inhibit abnormal patterns.
Task-specific training is also widely used, involving repetitive practice of functional activities to strengthen new neural pathways and encourage independent joint movement. This can include exercises that isolate components of the movement, such as working on knee extension with the hip flexed to prevent the entire synergy from activating. Motor learning principles, emphasizing repetition and feedback, help reinforce desired movements and reduce the dominance of the synergy.
Orthotics or braces, such as an ankle-foot orthosis (AFO), can provide support and help maintain a more functional position of the foot and ankle, counteracting plantarflexion and inversion. This external support assists in improving walking mechanics and stability. Pharmacological interventions address symptoms like spasticity, which commonly co-occurs with synergy patterns. Botulinum toxin injections can temporarily reduce muscle overactivity in specific muscles, allowing for a window of opportunity for more effective therapy. Oral medications like baclofen may also be used to reduce generalized spasticity.