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Orthopaedic Surgery

Adolescent Idiopathic Scoliosis (AIS)

Adolescent idiopathic scoliosis, also called AIS, is a condition that affects children or adolescents between the age of 9 and young adulthood and is characterized by the presence of an abnormal lateral curvature of the spine. This curvature causes the spinal column to bend to the left or the right, in the shape of an S or a C. Adolescents with scoliosis are generally otherwise healthy, and most are completely active, despite the curvature in the spine. AIS is by far the most common type of scoliosis, of which there are several. In fact, as many as fourof all children between 9 and 14 years old have detectable scoliosis. Girls, or young women, are at higher risk than boys, or young men, with 60 to 80 of all cases occurring in females. AIS may begin to manifest itself at the initial onset of puberty or become apparent or worsen during an adolescent's growth spurt. AIS is also the type of scoliosis with the best prognosis, the estimate of how debilitating the condition will be after diagnosis. Most children with AIS do not develop worsening curvature, and therefore treatment usually begins with observation only.

Facts about AIS:

• Scoliosis is technically defined by the presence of a lateral curvature in the spine of >10 degrees deviation from straight upright (described further in the 'How is it diagnosed?' section).
• While AIS is, overall, more common in adolescent girls than boys, the presence of small curves is actually equally common in boys and girls. However, many more adolescent girls than adolescent boys have severe curves, suggesting that the condition may be more likely to progress in girls.
• The incidence of the AIS is higher in children with a positive family history (i.e. a family relative also had/has scoliosis).
• While there are several types of scoliosis for which the causes or origins of the disease are well understood, adolescent scoliosis is considered idiopathic, which means the causes are, for the most part, unknown.
• Adolescents with small curves usually do not experience pain from AIS. When curves become larger or progress quickly, the condition can cause some back pain for patients, but also requires that a thorough diagnostic workup be performed to rule out any other spinal conditions or other possible causes for the pain.

The normal spine

The spine, or spinal column, as it is also called, is a complex structure made up of 33 vertebrae, or bony segments, arranged vertically in succession from just below the skull to the tailbone. The spine has two main functions: to support the weight of the skull and upper body, and to provide a protective encasement for the spinal cord, the long, cylindrical nervous structure that sends messages to and from the brain and the rest of the body. The vertebrae are attached to other vertebrae above and below them by a number of ligaments, thick fibrous structures found throughout the musculoskeletal system that attach bones to other bones. The connection points between the vertebrae are called joints, in which small areas of smooth cartilage lined with a lubricating material, known as synovial fluid, allow the bony vertebrae to slide past each other with minimal friction, allowing movement. Unlike joints such as the knee or elbow, which allow for considerable movement, each joint of the spinal column allows for very little movement because of the number of tightly attached ligaments, thereby ensuring the strength and stability of the vital supportive column. However, the joints of the spine act collectively, with the sum of movements in all the joints allowing movements such as bending forward, back, and to the side.

The normal spine actually has a number of natural curves to it, which stems from the evolution of humans from four-legged mammalian ancestors who walked on the ground bent over, with the spine parallel to the ground. However, these normal curves are antero-posterior curves only; that is, they can only be seen when looking at the spine from the side. On the other hand, when looking from directly behind or in front of a person, the spine maintains a rigid upright structure, like a straight line. In other words, there are normally no lateral curves to the human spine. This upright structure is maintained by the body's natural positioning system, known as proprioception. When we move around on a normal basis, special nerve sensors called proprioceptors in the regions of all of our joints send millions of rapid signals to the brain with even the slightest movements. The brain processes all of these signals, monitoring exactly what the different parts of the body are doing, and sending signals back down to the muscles to alter the position of our body parts. Because the spine is made up of a large number of joints, all of which have their own proprioceptors, the brain is able to maintain finely tuned control over the spine and preserve its straightness, eliminating even the slightest lateral curves on a normal basis. Should there be even minor defects in the communication from the proprioceptors to the brain or in the brain's processing of the signals, one's ability to maintain an upright position would be compromised.

Causes of AIS

As previously mentioned, the exact cause of AIS is unknown. However, the considerable amount of medical research that has gone into understanding scoliosis has led to the acceptance of several hypotheses for how AIS may develop.

For example, research studies have revealed that a high proportion of adolescents with AIS have deficits in proprioception, described above. Most adolescents with AIS therefore don't even realize when they are not positioning themselves exactly upright much of the time. As a result, the spine may progressively bend to one side to compensate for the deficit. In time, that bend maintains itself because the ligaments surrounding the vertebral joints may get stretched and then tighten according to whatever position is most often maintained. Because that position is one of lateral bending in some children, AIS ensues. As a result of the condition, the spine also rotates slightly on its axis, which causes the ribs on one side to rotate as well. The lateral bending can be difficult to assess on physical exam, because the spine is buried under several layers of muscle and skin, and cannot be viewed clearly without an X-ray. It is the rotational change of the spine that actually gets detected most frequently on physical exam, and a full clinical work-up for scoliosis follows (described further in the 'How is AIS diagnosed' section).

A second possible cause of developing AIS is simply genetic inheritance. Because the condition is more common among adolescents whose family members had the condition, many scientists believe that a set of genes that code for the deficits causing scoliosis may be inherited in a dominant fashion. However, because the incidence of scoliosis does not occur in a traditional dominant pattern (i.e., not every child of parents who had scoliosis develops the condition, and vice versa), most likely not everyone expresses these genes to the same extent. This suggests that the scoliosis gene, or genes, may be dominant, but there is variability in genetic penetrance, which means that the degree to which the genes end up affecting an individual is quite unpredictable.

Research has suggested that several sites on more than one chromosome may be involved in the development of scoliosis. Another hypothesis gaining greater acceptance is that scoliosis is not one condition, but actually a number of different conditions, with the same clinical presentation, despite each having its own unique genetic origins. Each of these conditions may also have a different prognosis, which might explain the wide range of curve severity and rates of curve progression between different patients.

Despite the growing support for both of these hypotheses, much about AIS remains to be discovered and fully understood. As a result, there is ongoing research at a number of academic medical centers throughout the U.S., attempting to further unlock these medical mysteries and improve the treatment and prevention of this common musculoskeletal condition.

Diagnosing AIS

Adolescent idiopathic scoliosis is usually first suspected during a standard physical examination by a pediatrician or primary internist, or during a screening test at school. Such examinations include the Adams forward bending test, which consists of the child or adolescent, with his/her shirt removed, bending forward at the waist until the spine is parallel with the floor, while the physician observes the shape of the spine as it bends. As mentioned above, the abnormal rotation of the spine, called truncal rotation, will create a rib hump characteristic in AIS, in which the ribs on one side protrude slightly, compared to the other side, when bending forward. Mild curves in the spine generally do not cause back pain early in the condition, but may cause some stiffness or difficulty in bending forward completely, which may also be observed by a physician. In either case, a follow-up standing x-ray series, in which several X-rays are taken from different directions with the child standing upright, is recommended to make a definitive diagnosis of scoliosis. As mentioned before, this requires the presence of a curvature angle of at least 10 degrees, measured with the Cobb method.

Finally, a neurologic exam of the back and extremities will be performed to insure that no other spinal conditions are present and that the spinal cord is not being affected by the presence of the abnormal curvature.

Treating AIS

Decisions regarding the appropriate treatment for AIS depend mostly on two factors: the severity of the spinal curvature and the physical maturity of the patient. Because different children grow at different rates and experience growth spurts at different ages, the age of the patient is not as important as the child's skeletal age, so to speak. Skeletal age is determined by how completely a child’s bones have undergone a process known as ossification, in which the cartilage that initially makes up a child's bones is replaced by hard bone tissue, as found in adults. Orthopaedic surgeons assess this process by examining the pelvis bone on X-rays, and assign a Risser grade to that child, which reflects their skeletal maturity. Also, because growth patterns in girls and boys tend to be different, the sex of the patient plays a role in treatment as well.

The majority of children or adolescents will have mild curves (10-25 degrees) when AIS is first diagnosed, and will therefore be treated only with observation. This entails simply that the child be seen regularly by an orthopaedic surgeon, who will monitor the possible progression of the curve with several standing X-rays over time. The spinal curves of most children do not progress, and no further treatment is needed. However, if the curve becomes more severe, the patient may require bracing treatment.

Physically immature patients with moderate curves (between 25 and 40 degrees) generally require treatment with a brace. Girls are deemed ‘physically immature’ if they are premenarcheal (i.e. have not had their first period), and if their bones have not yet undergone significant ossification. Boys will usually receive bracing at slightly older ages than girls, because the growth of their spines continue at older ages than girls, on average, and one goal of bracing is to begin treatment before the spinal growth period is completed.

Bracing treatment is initiated with a child being fitted for a properly sized external brace. Several types of braces exist, such as the TLSO (thoracic-lumbar-sacral orthosis) brace, Milwaukee brace, Boston brace, Charleston bending brace, and Providence brace, but all are designed with the same fundamental principle in mind: to prevent progression of the spinal curve and maintain an upright vertebral column. Advances in brace design have allowed for more comfortably fitting devices with abundant padding, so if the brace is uncomfortable, it is important to speak with your orthopaedic surgeon to make changes that ensure compliance with wearing the brace. Within two to three weeks of the fitting, wearing of the brace should be increased in accordance with the brace schedule, provided by your orthopaedic surgeon. The more a child or adolescent deviates from that schedule, the more likely the curve is to progress and ultimately require surgical treatment. Provided there is no further curve progression, the brace is usually worn until an adolescent reaches full physical maturity, a point that varies in age for different individuals. A set of exercises is often prescribed in conjunction with bracing treatment. These exercises are not designed to correct scoliosis in any way, but rather to strengthen the back muscles that would otherwise become weak from the immobilization caused by the brace. With adherence to the bracing schedule, this bracing treatment is extremely successful, and many adolescents even have fully corrected curves after removal of the brace. However, inevitably in some patients, the curve worsens, and surgery becomes the best treatment option.

Physically immature patients with severe curves (>40 degrees) are at a high risk of even further curve progression, and therefore usually require surgical treatment. Curve progression is more unpredictable in physically mature patients, but if the curve reaches >50 degrees, surgery is also warranted for these people. Scoliosis surgery consists of spinal fusion, in which two or more of the vertebrae are fused together with bone bridges made of bone grafts, and/or instrumentation, in which metal rods are attached to the spine to maintain curve correction. Surgeries may be performed through a posterior approach, in which the operation is performed with an incision in the back, or also with an anterior approach, which is a more extensive surgery that requires making an opening in the chest wall to reach the front part of the spinal column. Surgeries utilizing the anterior approach have been revolutionized in the last decade or so with the advent of thoroscopic spine surgery, in which smaller openings are made and special cameras are used to visualize the spine, thereby minimizing scars and recovery time. For a more detailed description of this type of surgery, click here. Because of the stability and effectiveness of the devices used in these spine operations today, patients are usually able to walk the day following their surgery, and hospital stays are generally under one week. The majority of children or adolescents return to school within two weeks and can often return to full athletic activity within a year, though contact sports are not recommended.

Coping with AIS

Scoliosis may seem like a difficult condition to live with, particularly during adolescence, which is a transitional period involving not only physical growth, but emotional instability as well. However, most patients with AIS live normal lives, without any pain or limitations in physical activities or daily functioning. External bracing treatment, as well, might be perceived as being particularly inconvenient for adolescents. However, an extensive study performed by our research group demonstrated that the quality of life of adolescents treated with the necessary braces is no different that the quality of life of adolescents treated with observation alone, with regard to activities, relationships with peers, general happiness and other parameters. There was also no difference between adolescent girls and boys. This result is consistent with a number of other research studies as well. Thus, whatever treatment an adolescent receives for AIS, he or she may be expected to live a normal, healthy, active life, and walk tall into adulthood.

For more information

You may have other questions about AIS that are not answered in the above summary. If your child is not in the adolescent age group or may have another type of scoliosis, please refer to our descriptions of other types of scoliosis, found here.