The Biomechanical Mechanisms Behind Adolescent Idiopathic Scoliosis
Original Editors - Julia Ratz as part of The University of Waterloo Clinical Biomechanics Project
Background Information[edit | edit source]
Definition[edit | edit source]
Prevalence[edit | edit source]
Adolescent idiopathic scoliosis is most common in those 11-18 years old. Approximately, 1-4% of the adolescent population is affected by this condition, with females being more commonly affected. AIS affects females more than males at a ratio of 1.5 females for every affected male, however, this ratio can range up to three females affected for every male.
Formation[edit | edit source]
Adolescent idiopathic scoliosis is formed by an overgrowth of the anterior column of the spine relative to the posterior column. It is said that the larger the overgrowth in the anterior column, the larger the visual deformity of the patient’s spine. The lack of the growth in the posterior column impedes the growth of that of the anterior. Vertebral bodies become distorted and rotate within the spine in order to make room for themselves due to the impediment of the anterior column.
Assessment[edit | edit source]
Treatment[edit | edit source]
Mild to moderate cases of AIS can be treated with conservative treatment methods. Pain can be reduced in these cases by patients utilizing the Schroth method, braces, and taping. There is insufficient evidence to support taping and bracing at this time. However, in the few studies completed on these topics they have been shown to help reduce pain. Severe cases of AIS can be treated with surgery. Surgery is usually recommended if other treatment methods are not working or if the Cobb angle is greater than 45 to 50 degrees.
Mechanisms of Condition[edit | edit source]
Spinal Shear Loads[edit | edit source]
As previously mentioned, there is an overgrowth of the anterior aspect of the spine in patients with AIS. The anterior growth of the spine causes a rotation of the vertebral bodies. Vertebral bodies must rotate to make room for themselves as the anterior aspect grows. When the vertebral bodies rotate, the spinal shear loads are directed dorsally. Shear loads are directed dorsally even during axial loading. Normally, shear loads are applied in all directions when under axial loading. The redirection of shear loads results in tissues being stressed that are not normally stressed, leading to increased pain and stiffness.
Spinal Compression[edit | edit source]
A 10% increase in spinal compression in those with AIS during upright standing is seen as a result of the rotation of the vertebral bodies. The increase in spinal compression that is seen in this population affects their ability to complete functional activities. For example, a recent study found increased spinal compression force in those with adolescent idiopathic scoliosis when wearing a backpack, compared to those without AIS. The same study concluded if a backpack is worn on the front of the body the spinal compression is increased even more in those with AIS. The increased spinal compression when the backpack is on the front of the body is a result of the overgrowth of the anterior aspect of the spine. This demonstrates how functional activities are affected in those with this condition.
Trunk Stability[edit | edit source]
Decreased trunk stability is seen in those with adolescent idiopathic scoliosis as a result of the abnormal curvature. The abnormal curvature of the spine pulls and strains muscles leading to some muscles becoming weaker than others. The increased strain on certain muscles and decreased strength of other muscles leads to trunk instability. Trunk instability affects other functional activities in those with AIS as it decreases the ability to balance. A decreased ability to balance can cause problems when it comes to quiet standing and gait, amongst other activities.
The instability of the trunk can also cause ventilatory restriction as the instability strains back and ventilatory muscles. The right thoracic curve is the most common to cause respiratory impairment in adolescents, as well as reduction in lung volumes and inspiratory muscle weakness. These ventilatory impairments can cause significant decrease in functional activities in those with AIS.
Muscular Tone and Stiffness[edit | edit source]
Muscular tone and stiffness are greatly affected in those with AIS, especially on the concave side of the spine. Muscles are shortened on the concave side and lengthened on the convex side. Increased muscular tone and stiffness can lead to increased pain and decreased range of motion. Muscular tone and stiffness are correlated with the severity of the case of scoliosis, meaning the more severe the case, the more tone and stiffness that will be present.
Range of Motion[edit | edit source]
Those with adolescent idiopathic scoliosis often have a decreased range of motion in the frontal plane of the pelvis, in the hips, and in the shoulders. Decreased range of motion is believed to be due to stiffness of the spinal deformity and prolonged bilateral muscle activation. The quadratus lumborum, erector spinae, gluteus medius, and semitendinosus are some of the muscles that experience prolonged muscle activation. Muscular dysfunction and potential diseases linked to motor control activity are believed to be the culprit of the prolonged activation. As the severity of adolescent idiopathic scoliosis increases the range of motion decreases.
Conclusion/Summary[edit | edit source]
Adolescent idiopathic scoliosis is the abnormal curvature of the spine with a Cobb angle greater than 10 degrees when measured in the coronal plane. The greater the Cobb angle, the more severe the symptoms. Symptoms begin to appear during ages 11-18, affecting more females than males. Functional activities such as wearing a backpack, balance during walking and quiet standing, and breathing can all be affected by this condition. AIS is caused by an overgrowth of the anterior aspect of the spine relative to the posterior aspect. The overgrowth causes the vertebral bodies to rotate amongst themselves.
Adolescent idiopathic scoliosis can be treated with conservative methods in mild to moderate cases. Conservative treatment methods include using the Schroth method, braces, and taping. Intense treatment methods (such as surgery) are used in severe cases of AIS. Surgery is used to treat those with Cobb angles greater than 45 to 50 degrees.
Spinal shear and compression are increased in those with adolescent idiopathic scoliosis as a result of the overgrowth of the anterior aspect of the spine and the rotation of vertebral bodies. Trunk stability is decreased due to muscular differences on the concave side of the spine compared to the convex side. Trunk instability leads to balance issues and ventilatory problems. Range of motion is decreased in the frontal plane of the pelvis, the shoulders, and the hips in those with this condition due to stiffness of the spine and prolonged bilateral muscle activation.
Related Articles[edit | edit source]
References[edit | edit source]
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