Cerebral Palsy

Cerebral palsy is, at its root, a problem of the brain rather than the spine. An early injury to the developing brain disturbs the signals that control muscle tone, balance and posture, and the result is a lasting disorder of movement that does not itself get worse over time. The spine, however, sits at the centre of the body's posture, and it depends for its straightness on a balanced pull of the muscles of the trunk and on the ability to hold oneself upright. When that balance and control are disturbed, the spine is left vulnerable to deformity as the child grows.

The link between cerebral palsy and the spine is, therefore, an indirect one. The brain injury does not bend the spine directly. Instead, it removes the steady, symmetrical muscular support that keeps a growing spine straight, and it is this loss of control, acting over years of growth, that allows a curve to develop. This is why the spinal deformity of cerebral palsy is described as neuromuscular in origin, to distinguish it from the idiopathic scoliosis of otherwise healthy adolescents.

Seeing cerebral palsy from the standpoint of the spine means recognising that the severity of the spinal problem tracks closely with the severity of the underlying condition. The children whose movement is least affected, who walk independently, are at relatively low risk of a significant curve. Those at the other end of the spectrum, who cannot sit or stand unsupported, are at much higher risk, and it is in this group that the spine becomes a central concern.

The system used most widely for describing severity is the Gross Motor Function Classification System, usually shortened to the GMFCS. It was developed by Palisano and colleagues and sorts people with cerebral palsy into five levels according to what they can do, rather than according to the type of cerebral palsy they have. At level one, a person walks without restriction; at level two, walking is possible but with some limitation; at level three, walking requires a handheld mobility aid; at level four, self-mobility is limited and the person is largely transported or uses powered mobility; at level five, the person is transported in a manual wheelchair and has very limited ability to control their own posture against gravity.

The reason the GMFCS matters so much to the spine is that the risk and severity of scoliosis rise steeply across these levels. The non-ambulant levels, four and five, and level five in particular, carry by far the greatest risk of a severe spinal curve. Much of what follows on this page applies most strongly to those at these levels, because it is there that neuromuscular scoliosis is most common, most severe and most likely to require consideration of surgery.

The development of a spinal curve in cerebral palsy follows from the loss of balanced muscular control over a growing skeleton. A healthy spine is held straight not by its bones alone but by a continuous, symmetrical tug of the muscles of the trunk and the constant small adjustments of posture that an intact nervous system makes without conscious thought. In cerebral palsy these mechanisms are disturbed. Muscle tone may be increased on one side and reduced on the other, trunk muscles may be too weak to hold the body upright, and the automatic corrections that keep the trunk centred over the pelvis are impaired.

Against this background, the spine of a growing child is left without the even support it needs to grow straight. A small asymmetry of tone or posture tends to be reinforced rather than corrected, and over the years of growth the spine settles progressively into a sideways curve. Because the deforming forces act along the whole length of the trunk rather than at one segment, the resulting curve tends to be long and sweeping, often taking the form of a single broad C that runs through much of the spine. A defining feature of this neuromuscular curve is its tendency to involve the pelvis. As the curve runs down towards its base, it frequently carries on into the pelvis itself, tilting it out of the horizontal so that one side sits higher than the other. This is called pelvic obliquity.

The classic pattern is a long C-shaped curve that extends across the thoracic and lumbar regions together, frequently reaching down to the pelvis. Because the muscular control that would normally produce compensating curves is itself disturbed, the body is less able to balance the deformity, and the trunk can come to lean markedly to one side. The curve tends to be collapsing in nature, folding the trunk down towards the pelvis rather than holding a balanced posture.

The involvement of the pelvis is central to this picture. Pelvic obliquity is the feature that most directly disturbs sitting, because a tilted pelvis cannot provide the level, symmetrical base that comfortable, stable sitting requires. The combination of a long collapsing curve above and an oblique pelvis below is, in many ways, the signature of the spinal deformity seen in severe cerebral palsy, and much of the surgical thinking in this field is directed at correcting both together.

The spinal curve of cerebral palsy is not static. Where the brain injury itself is non-progressive, the spinal deformity it gives rise to is anything but, and the natural tendency of these curves, particularly the larger ones in the most severely affected children, is to increase over time. Curves often begin to appear during childhood and tend to progress through the growth spurt of adolescence, when the rapid lengthening of the spine offers the deforming forces their greatest opportunity.

An important feature, and one that distinguishes neuromuscular scoliosis from the idiopathic scoliosis of healthy adolescents, is that the curve does not necessarily stop progressing once growth is complete. In idiopathic scoliosis, smaller curves tend to stabilise at skeletal maturity. In cerebral palsy, by contrast, the larger curves can continue to increase into adult life, because the underlying loss of muscular control that drives them does not resolve with maturity. Systematic reviews of progression after skeletal maturity describe continued increase in a substantial proportion of patients, particularly those whose curves were already large at the end of adolescence and those most severely affected.

For a person who cannot stand or walk, the most important consequence of a spinal curve is its effect on sitting. As the trunk leans and the pelvis tilts, the even base that comfortable sitting depends on is lost. Weight is thrown disproportionately onto one buttock, which raises the risk of pressure problems over the skin in that area. The trunk may need to be propped or supported to prevent it folding to one side, and the hands, which might otherwise be free for use, can become occupied in holding the body up. Head control, already often limited, can be further compromised when the trunk beneath is unstable.

There is a knock-on effect on care. A trunk that has collapsed to one side, with a tilted pelvis and uneven pressure, is harder to seat, harder to position, and harder to keep comfortable. Specialised seating systems, with moulded supports, tilt and pressure-relieving cushions, are widely used to accommodate the deformity and to maintain as level and as comfortable a posture as possible, and these form an important part of non-surgical management.

The spine in cerebral palsy cannot be considered in isolation from the hips, because the two are linked through the pelvis that sits between them. The hips in severe cerebral palsy are themselves at high risk, the imbalanced muscle pull tending to draw the head of the femur progressively out of its socket in a process of subluxation and, ultimately, dislocation. A related pattern is the windswept deformity, in which both legs are drawn over to the same side, one hip turning inwards and the other outwards.

Studies of the patterns of deformity in non-ambulant cerebral palsy have shown that the direction of the spinal curve, the direction of the pelvic obliquity, the direction of the windswept hips and the side of hip dislocation are not independent of one another but tend to follow a consistent, linked pattern. The practical importance of this is that the spine, the pelvis and the hips form a single chain, and the assessment of cerebral palsy scoliosis is, in reality, an assessment of the whole hip-pelvis-spine complex.

When a curve in cerebral palsy becomes severe, progressive and disabling, the surgical option that is most often considered is a long posterior spinal fusion, frequently extending down to include the pelvis. The aim of such an operation is to straighten the spine as far as is safe, to level the pelvis, and to fuse the corrected position permanently into a single solid block of bone, so that the deformity can no longer progress and a balanced, level seated posture is restored.

The reason these operations are so extensive is the nature of the curve. Because the deformity is long and collapsing and frequently carries into the pelvis, a short fusion of a few segments cannot address it. Published series using modern segmental screw techniques describe substantial corrections of both the spinal curve and the pelvic obliquity, frequently of the order of three-quarters of the deformity, with the goal of producing a level, balanced and comfortable sitting position. This is reconstructive surgery aimed at function and comfort rather than at producing a normal spine.

On the side of benefit, the operation can achieve a large and durable correction of a deformity that would otherwise continue to worsen. It can level the pelvis, restore a balanced seated posture, halt the progression of the curve, and address the problems of sitting, pressure and care that the deformity creates. Studies that have asked carers and families about the results have frequently reported high levels of satisfaction and meaningful improvements in ease of seating, comfort and care, although the evidence on formal quality-of-life measures is more mixed.

On the side of risk, this is among the higher-risk operations in elective orthopaedics, precisely because of the comorbidities the patients carry. Large series document substantial major complication rates, with problems of the chest and lungs, wound and deep infection, considerable blood loss, and difficulties related to nutrition and the gut all featuring prominently. A small but real perioperative mortality is reported in the literature, reflecting the fragility of the most severely affected patients. Reoperation, often for problems with the wound or the instrumentation, is not uncommon.

Nutrition is a central concern. Difficulty with feeding and swallowing is common in severe cerebral palsy, and undernutrition is associated with higher rates of wound and other complications after major surgery. Optimising nutritional status before an operation, sometimes with the help of feeding support, is widely regarded as an important part of reducing risk. The chest is the other dominant concern. Respiratory function is frequently impaired in severe cerebral palsy, through a combination of weak respiratory muscles, the mechanical effect of the deformity itself on the rib cage and lungs, a tendency to recurrent chest infection, and the risk of aspirating food or secretions. Seizure disorders, problems with the gut and bowel, and the general frailty that accompanies severe neurological disability all add to the picture.

The outlook in cerebral palsy and the spine depends above all on the severity of the underlying condition. For those who are mildly affected and able to walk, a significant spinal curve is relatively uncommon. For those at the severe end of the spectrum, who cannot sit or stand unsupported, the spine is one of the central orthopaedic issues, with a high likelihood of a curve that develops in childhood, progresses through adolescence, and may continue to worsen into adult life. Where surgery is undertaken, the realistic aim is a level, balanced and comfortable seated posture and a halt to progression, rather than a normal spine, with reported results often good when judged in those terms.

This page is general medical education and is not a substitute for individual advice. New or worsening weakness, numbness, saddle numbness or any disturbance of bladder or bowel control requires urgent assessment.

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This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.