Spastic diplegia is the most common form of cerebral palsy, a group of neurological disorders affecting movement and posture. This condition originates from damage to the developing brain, typically before or shortly after birth. Its defining characteristic is a motor impairment that primarily affects the legs, though the arms are usually involved to a much lesser extent. The condition is non-progressive, meaning the brain injury itself does not worsen over time, but the resulting physical symptoms can change as the child grows.
Defining Spastic Diplegia
Spastic diplegia is classified as a subtype of spastic cerebral palsy. The name itself offers a clear definition: “spastic” refers to hypertonia, or increased muscle tone, which results in stiff, tight muscles and exaggerated reflexes. This rigidity is due to an inability of the brain to properly regulate muscle activation, causing the muscles to be constantly contracted.
The term “diplegia” indicates that two limbs are affected, predominantly the lower limbs. While the legs are the primary site of severe spasticity, the arms and upper body may also exhibit milder symptoms, such as slight stiffness or clumsiness. The injury responsible is located in the brain’s motor cortex, specifically impacting the nerve pathways that control voluntary movement in the lower body.
Underlying Causes and Risk Factors
The root cause of spastic diplegia is damage to the brain’s white matter, which is responsible for transmitting signals between nerve cells and the spinal cord. This white matter injury most often occurs in the periventricular region, the area surrounding the brain’s ventricles, resulting in a condition known as periventricular leukomalacia (PVL). PVL is the most common underlying pathology leading to spastic diplegia because the nerve fibers controlling leg movement are located closest to this vulnerable area.
A lack of sufficient blood flow or oxygen to the brain tissue, known as hypoxia or ischemia, is the direct trigger for PVL. The largest risk factor for this type of injury is premature birth, particularly before 32 weeks gestation, as the developing white matter is extremely fragile at this stage. Low birth weight, infections passed from mother to baby during pregnancy, and unstable blood pressure or oxygen levels shortly after birth are also associated factors.
How Spastic Diplegia Affects Movement
The defining symptoms of spastic diplegia manifest as observable difficulties with mobility and posture. The constant, involuntary muscle tightness in the legs, hips, and pelvis creates distinct abnormal walking patterns, or gaits.
One of the most recognized is the “scissoring gait,” where the severe spasticity in the hip adductor muscles causes the legs to cross over one another as the person walks. Another common presentation is toe walking, known as equinus gait, which results from hypertonia in the calf muscles pulling the heel upwards. The muscle imbalance can also lead to a “jump knee” or “crouch gait,” where the hips and knees remain bent due to tightness in the hamstrings and hip flexors. Over time, this chronic tension can cause secondary orthopedic issues, such as joint contractures and bony deformities, because the uneven muscle pull interferes with normal growth and skeletal alignment.
Managing the Condition
Management of spastic diplegia relies on a comprehensive, multidisciplinary approach focused on minimizing spasticity and maximizing functional independence.
Physical and Occupational Therapy
Physical therapy (PT) and occupational therapy (OT) are foundational elements. They aim to maintain or increase range of motion, build muscle strength, and teach adaptive strategies for daily activities. Therapists utilize stretching, strengthening exercises, and often employ orthotic devices like ankle-foot orthoses (AFOs) to maintain proper alignment and prevent contractures.
Pharmacological Interventions
Pharmacological interventions are frequently used to directly manage the high muscle tone. Muscle relaxants such as oral baclofen or tizanidine work systemically to reduce spasticity throughout the body. For more localized and severe spasticity, botulinum toxin injections can be administered directly into specific muscle groups, temporarily blocking nerve signals. In cases of severe, generalized spasticity, a surgically implanted intrathecal baclofen pump can deliver the medication directly to the spinal fluid, which often minimizes systemic side effects.
Surgical Options
Surgical options are considered when non-surgical methods are insufficient to control spasticity or address resulting deformities. Selective Dorsal Rhizotomy (SDR) is a neurosurgical procedure that permanently reduces spasticity by selectively cutting overactive sensory nerve roots in the lower spinal cord. Orthopedic surgeries, such as tendon lengthening or bone realignment procedures, may also be performed to correct fixed joint contractures and deformities. These interventions require intensive physical therapy afterward to maximize the benefits of improved muscle tone and range of motion.