Adolescent idiopathic scoliosis (AIS) is a progressive growth disease that affects spinal anatomy, mobility, and left-right trunk symmetry. The disease can modify human gait.
By far the most common type of scoliosis is one in which the cause is not known. It is called “idiopathic” or adolescent idiopathic scoliosis (AIS). Although significant ongoing research continues in this area, including the genetic basis for AIS, there are no identifiable causes for this condition today. Despite this, we currently have accurate methods to determine the risk for curve progression of scoliosis and good methods of treatment.
see Lenke Classification of AIS
There are significant efforts being made toward identifying the cause of AIS, but to date there are no well-accepted causes for this particular type of scoliosis. The vast majority of patients are otherwise healthy and have no previous medical history. There are many theories about the cause of AIS including hormonal imbalance, asymmetric growth and muscle imbalance. Approximately 30% of AIS patients have some family history of scoliosis, and therefore there seems to be a genetic connection. Many Scoliosis Research Society members are working to identify the genes that cause AIS, and this knowledge continues to expand at a rapid pace. Most likely, there will be many genes associated with scoliosis and each may be helpful in detecting scoliosis and determining the risk for progression of the curve. A genetic screening test, called the ScoliScore™ is available as an adjunct to clinical and x-ray information to determine risk of progression in Adolescent Idiopathic Scoliosis. It is currently used in Caucasian (North American, European, Eastern European, Middle Eastern) patients between the ages of 9 and 13 years with a mild scoliotic curve (less than 25 degrees). The stated goal of the test is to determine the risk that the curve will increase to 40 degrees or more. Thus far independent verification of the test has not been done.
Adolescent idiopathic scoliosis generally does not result in pain or neurologic symptoms. The curve of the spine does not put pressure on organs, including the lung or heart, and symptoms such as shortness of breath are not seen with AIS. When scoliosis begins in adolescence patients often have some back pain, typically in the low back area. Although it is often associated with scoliosis, it is generally felt that the curvature does not result in pain.
Low back pain is not uncommon in adolescences in general. Many teens experience back pain due to participating in a large number of activities without having good core abdominal and back strength, as well as flexibility of the hamstrings. Adolescent idiopathic scoliosis generally does not result in pain or neurologic problems. If these symptoms occur, further evaluation and testing may be necessary to include an MRI.
Daryabor et al., selected 33 studies investigating the effect of scoliosis deformity on gait parameters and energy expenditure during walking. Most of the studies concluded no significant differences in walking speed, cadence and step width in scoliosis patients and normal participants. However, patients showed decreased hip and pelvic motion, excessive energy cost of walking, stepping pattern asymmetry and ground reaction force asymmetry.
There is a consistent lack evidence of the effect of scoliosis on temporal spatial and kinematic parameters in AIS patients as compared with normal people. However, further research is needed to assess the effect of scoliosis on gait and energy consumption 1).
A retrospective study of 77 consecutive cases involving 56 female and 21 male patients with Lenke Type 1 main thoracic curve AIS who underwent single-stage posterior correction and instrumented spinal fusion with pedicle screw fixation between July 2009 and July 2012.
The patients' mean age at surgery was 15.79 ± 3.21 years. All patients had at least 1 year of follow-up.
Radiological parameters in the coronal and sagittal planes, including Cobb angle of the major curve, side-bending Cobb angle of the major curve, thoracic kyphosis (TK), correction rates, and screw density, were measured and analyzed. Screw densities (calculated as number of screws per fusion segment × 2) of < 0.60 and ≥ 0.60 were defined as low and high density, respectively. Titanium rods of 5.5 mm and 6.35 mm diameter were defined as low and high stiffness, respectively.
Patients were divided into 4 groups based on the type of rod and density of screw placement that had been used:
Group A, low-stiffness rod with low density of screw placement
Group B, low-stiffness rod with high density of screw placement
Group C, high-stiffness rod with low density of screw placement
Group D, high-stiffness rod with high density of screw placement.
The mean coronal correction rate of the major curve, for all 77 patients, was (81.45% ± 7.51%), and no significant difference was found among the 4 groups (p > 0.05).
Regarding sagittal plane correction, Group A showed a significant decrease in TK after surgery (p < 0.05), while Group D showed a significant increase (p < 0.05); Group B and C showed no significant postoperative changes in TK (p > 0.05).
The thoracic kyphosis (TK) restoration rate was highest in Group D and lowest in Group A (A, -39.32% ± 7.65%; B, -0.37% ± 8.25%; C, -4.04% ± 6.77%; D, 37.59% ± 8.53%). Screw density on the concave side was significantly higher than that on the convex side in all the groups (p < 0.05).
For flexible main thoracic curve AIS, both rods with high stiffness and those with low stiffness combined with high or low screw density could provide effective correction in the coronal plane; rods with high stiffness along with high screw density on the concave side could provide better outcome with respect to sagittal TK restoration 2).