Cerebral palsy (CP) is defined by the US National Institute of Neurological Disorders and Stroke as a group of neurological disorders “that appears in infancy or early childhood and permanently affects body movement and muscle coordination. CP is caused by damage to or abnormalities inside the developing brain that disrupt the brain’s ability to control movement and maintain posture and balance. The term cerebral refers to the brain; palsy refers to the loss or impairment of motor function.”
Structure and Function
CP is a static encephalopathy (a non-progressive brain disorder) that usually manifests as a disorder of movement. Babies with cerebral palsy do not roll over, sit, crawl or walk normally; older children with CP can present with poor coordination, stiff and weak muscles.
CP is primarily an upper motor neuron or movement disorder – however, depending on the size and location of the brain lesion, CP may affect speech, swallowing, and/or cognition. Cognitive problems can be a feature of CP, but are not always found. Any injury that occurs to the brain before the age of 2 may cause cerebral palsy.
CP may be classified physiologically (Table 1), anatomically (Table 2), or functionally. The physiological classification is based on the affected location of the brain lesion. The anatomic classification is defined by the affected limbs. A functional classification is based largely on the individual’s mobility. Because certain levels of function that might be described in a classification system - jumping, for example - are not expected to be present in very young children, functional classification is not maximally reliable until approximately 6 years of age or older.
The “static” aspect of the encephalopathy implies that the lesion which affects the brain does not expand or change with time - and that is true. However, the musculoskeletal manifestations of CP are not necessarily static. Indeed, the musculoskeletal manifestations of CP often worsen as the child grows. This occurs because normal muscle development depends on the appropriate neurological signals - and in CP, the damaged upper motor neuron fails to provide those signals. Normal bone and joint development, in turn, depend on normal muscle function and development.
The static brain lesions may also give rise to seizures, which is an additional cause of morbidity (and sometimes mortality) in patients with CP.
In simple language, CP is caused by brain damage during development in utero, during birth, or during very early infancy. There are a multitude of known factors that are linked to a higher chance of causing CP (see “Risk Factors,” below). In many cases, the cause of CP is unknown.
Children with CP will present with delayed developmental milestones, especially with independent sitting and ambulation.
The degree of severity varies greatly. Depending on the physiologic type of CP, general spasticity or dystonia and choreoathetosis (Involuntary muscle contractions causing writhing or twisting movements) may be appreciated.
Contractures of joints are common findings. Gait disturbances such as toe-walking, crouched gait, scissoring (Figure 1), among others, are frequently seen.
Torsional deformities of the long bones may be present. These develop via a normal remodeling response to the abnormal muscle forces acting across the joints of developing bones.
People with cerebral palsy often have low bone mineral density and thin cortices of the long bones. Contractures may impede full development of the articular surfaces.
Common deformities include increased femoral anteversion and external tibial torsion. Often, knee valgus, pes planovalgus or pes equinovarus are also present.
The hips in people with cerebral palsy are often subluxated or dislocated posterosuperiorly, due to a combination of abnormal muscle tone leading to abnormal acetabular development, increased femoral anteversion, and hip adduction and flexion contractures.
Neuromuscular scoliosis is also common in CP patients, especially in those with high levels of functional impairment (Figure 2).
There are no laboratory tests with which to diagnose CP; it is a clinical diagnosis based on clinical manifestations.
As the child grows, radiographs of the spine, hips, lower/upper extremities, and feet may show the effects of abnormal bone and joint development due to the underlying upper motor neuron lesion.
The spine may show a scoliotic curve, which is usually long and C-shaped (as shown above in Figure 2).
The hips may show increased femoral anteversion with apparent coxa valga, shallow acetabula and femoral head subluxation or dislocation (Figure 3).
Radiographs of the long bones may reveal evidence of abnormal axial plane malrotation due to abnormal growth and development.
The feet radiographs may reveal pes planovalgus, calcaneovalgus, or cavovarus deformities as well as hallux valgus and hallux interphalangeus (Figure 4).
Gait analysis – often paired with dynamic EMG - is routinely used as objective evidence when evaluating cerebral palsy, specifically for the disorders of movement and gait. Results from gait studies can guide surgical treatment in patients with CP.
CP is the most common cause of chronic disability in childhood. It occurs in about 1 to 3 per 1000 live births. However, if the child is born prematurely or with low birth weight, the incidence increases to around 90 per 1000 live births. The incidence may be slightly higher in families of lower socioeconomic status, although this difference is small.
The incidence of CP has remained stable in recent decades, despite improvements in neonatal care that have increased the survival rates among babies at risk for perinatal brain damage. These greater survival rates have been matched with improvements in perinatal care that help avert anoxic brain injury and CP.
The spine and hip pathology seen in CP patients can be seen in other neuromuscular disorders. However, proper history and physical exam can often distinguish between the various diagnoses.
A condition called familial spastic paraparesis may also look very similar to CP phenotypically. In this inherited condition, affected patients display weakness and spasticity, especially in the lower extremities. This condition, in contrast to CP, is progressive – that is, weakness and spasticity usually worsen as the patient ages.
Seizure activity can be seen in patients with CP. This may lead to further brain damage if left untreated. Choking and trouble swallowing may be present in those patients with CP who also have bulbar involvement. This may require G-tube placement for nutrition if the airway cannot be protected and there is a risk of aspiration. (Note that some children who can swallow normally may nonetheless benefit substantially from G-tube placement, simply as a means to ensure adequate nutrition.)
Treatment Options and Outcomes
The treatment of patients with CP is often complex and multi-disciplinary. Musculoskeletal providers treating CP patients often follow them from infancy through adulthood. Apart from assisting with the coordination of care to other providers, the musculoskeletal needs change throughout the life of the child living with CP.
The skills and services of physical therapists, occupational therapists, and orthotists are central to the treatment of children with CP. Physical therapy (PT) serves to help train and maintain mobility, which often relies on the use of aids such as crutches or walkers. PT programs focusing on stretching and specific muscle strengthening to help with ambulation and mobility are important, as are the use of various braces and orthoses to help prevent joint contractures and maintain appropriate joint alignment for ambulation. The treating orthopedist should also check at each visit to ensure that orthoses are still fitting appropriately, as children may grow out of their orthoses, or sometimes due to worsening deformity.
Medical treatment of the neuromusculoskeletal manifestations of CP is widely used. Common medications prescribed to combat global spasticity include baclofen and diazepam. Baclofen may be taken orally or administered intrathecally with an implantable pump to non-ambulatory patients. (Intrathecal pumps deliver the medication directly to the central nervous system and hence decrease the risk of systemic side effects.) Diazepam is taken orally. Both of these medications allow the musculature to relax but may lead to profound sedation if the dosage is too high. A neurologist skilled in the treatment of CP should follow these patients closely to help and strike the right balance between muscle relaxation and sedation.
Botulinum toxin A (“Botox”) may also be given to treat spastic CP patients. This medication is injected at the neuromuscular junction, and acts as an irreversible inhibitor to proteins at the axon terminal responsible for the release of acetylcholine, thereby disrupting the neuromuscular signal chain and preventing muscle fiber depolarization. Even though the toxin acts in an irreversible manner, after 3-6 months the clinical effect wears off due to protein turnover in the cell and new, uninhibited protein targets replace the inhibited ones. Patients treated with botulinum toxin A are then usually prescribed a physical therapy and bracing regimen. It is important to note that this therapy is only intended for spasticity; it is ineffective alone to correct a fixed joint contracture (though it can be a helpful adjunct to physical therapy which can decrease contracture).
When scoliosis is present, bracing may be employed to assist with sitting balance. However, unlike for idiopathic scoliosis, bracing does not prevent progression in neuromuscular scoliosis. Furthermore, unlike idiopathic scoliosis, curves tend to progress in neuromuscular scoliosis after skeletal maturity.
Surgical treatment may become necessary when following patients with CP. Surgery may be performed in an effort to improve ambulatory function, improve standing ability, relieve pain, improve hygiene, prevent worsening scoliosis and thus respiratory decline, prevent pressure ulcers, and sometimes for cosmetic concerns.
Contractures may be treated with tendon or muscle releases or lengthening procedures, especially in the lower extremities to improve gait. The treating surgeon should be warned, however, to avoid overlengthening the Achilles tendon, which may convert one gait problem into another. Crouch gait can be treated with distal femoral extension osteotomies and patellar tendon shortening or advancements. In-toeing or external rotation deformities may be treated with de-rotational osteotomies at the site of pathology (tibia or femur). Foot deformities, such as cavovarus foot, pes planovalgus, calcaneovalgus, and/or hallux valgus may be treated with tendon transfers, osteotomies, and/or fusions, as appropriate (Figure 5). When performing tendon transfers, split tendon transfers are often recommended to prevent over-correction.
Hip subluxation may be treated with adductor tenotomy, but only in mild cases in younger patients. In the setting of more severe subluxation, adductor tenotomy alone is not apt to be effective. Thus, when there is severe subluxation (or worse, when frank dislocation is present), femoral and/or pelvic osteotomies are often necessary in addition to adductor release. A common option for the femoral osteotomy is a varus de-rotation osteotomy of the proximal femur (Figure 6). Options for pelvic osteotomies include Dega osteotomy (if the triradiate cartilage is still open) or a Ganz versus shelf osteotomy (if the triradiate cartilage is closed). In addition, total hip replacement can also be used to address CP-associated hip arthrosis in adult patients (teens and older).
Scoliosis is often progressive and may be treated with posterior spinal fusion. Fusion to the pelvis is recommended if pelvic obliquity is present, especially in non-ambulators to improve wheelchair balance (Figure 7). Very stiff curves and large curves may require anterior release as well.
Life expectancy in CP is inversely correlated with the severity of disease. Patients with mild CP may have a normal life expectancy. By contrast, as many as 10% of severely affected patients will die in childhood. Respiratory failure is the most common cause of mortality in CP patients.
Outcomes following surgery are generally worse than outcomes for similar surgeries in unaffected patients. For example, the infection rate following spinal fusion surgery is much higher for CP patients than it is for idiopathic scoliosis patients.
Risk Factors and Prevention
Many known risk factors exist for CP (Table 3). Many of these environmental risk factors can be mitigated before & during pregnancy. However, controlling for these risk factors does not completely reduce the chances of being born with CP to zero.
Although the term “cerebral palsy” was not used until the late 1800s, the condition has been described since ancient times. William Osler was the first to coin the term “cerebral palsy.” During the polio epidemic, cases of polio and cerebral palsy were often confused, and CP was thought to be due to the polio virus to some extent.