Abstract
BackgroundAdolescent Idiopathic Scoliosis is the most common type of spinal deformity, and whilst the isk of progression appears to be biomechanically mediated (larger deformities are more likely to progress), the detailed biomechanical mechanisms driving progression are not well understood. Gravitational forces in the upright position are the primary sustained loads experienced by the spine. In scoliosis they are asymmetrical, generating moments about the spinal joints which may promote asymmetrical growth and deformity progression. Using 3D imaging modalities to estimate segmental torso masses allows the gravitational loading on the scoliotic spine to be determined. The resulting distribution of joint moments aids understanding of the mechanics of scoliosis progression.MethodsExisting low-dose CT scans were used to estimate torso segment masses and joint moments for 20 female scoliosis patients. Intervertebral joint moments at each vertebral level were found by summing the moments of each of the torso segment masses above the required joint.ResultsThe patients’ mean age was 15.3 years (SD 2.3; range 11.9–22.3 years); mean thoracic major Cobb angle 52° (SD 5.9°; range 42–63°) and mean weight 57.5 kg (SD 11.5 kg; range 41–84.7 kg). Joint moments of up to 7 Nm were estimated at the apical level. No significant correlation was found between the patients’ major Cobb angles and apical joint moments.ConclusionsPatients with larger Cobb angles do not necessarily have higher joint moments, and curve shape is an important determinant of joint moment distribution. These findings may help to explain the variations in progression between individual patients. This study suggests that substantial corrective forces are required of either internal instrumentation or orthoses to effectively counter the gravity-induced moments acting to deform the spinal joints of idiopathic scoliosis patients.Electronic supplementary materialThe online version of this article (doi:10.1186/s13013-015-0060-9) contains supplementary material, which is available to authorized users.
Highlights
IntroductionAdolescent Idiopathic Scoliosis is the most common type of spinal deformity, and whilst the isk of progression appears to be biomechanically mediated (larger deformities are more likely to progress), the detailed biomechanical mechanisms driving progression are not well understood
Adolescent Idiopathic Scoliosis is the most common type of spinal deformity, and whilst the isk of progression appears to be biomechanically mediated, the detailed biomechanical mechanisms driving progression are not well understood
Whilst the initial deformity may be due to a complex interplay of biomechanical, biochemical, and/or genetic factors, as well as growth asymmetries originating in the sagittal plane, it is widely accepted that scoliosis progression is predominantly a biomechanical process, whereby the spine undergoes asymmetric loading and alteration of vertebral growth in a “vicious cycle” [5, 6]
Summary
Adolescent Idiopathic Scoliosis is the most common type of spinal deformity, and whilst the isk of progression appears to be biomechanically mediated (larger deformities are more likely to progress), the detailed biomechanical mechanisms driving progression are not well understood. Whilst the initial deformity may be due to a complex interplay of biomechanical, biochemical, and/or genetic factors, as well as growth asymmetries originating in the sagittal plane, it is widely accepted that scoliosis progression is predominantly a biomechanical process, whereby the spine undergoes asymmetric loading and alteration of vertebral growth in a “vicious cycle” [5, 6]. Supine imaging modalities such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) have made possible 3D reconstructions of the spine, which allow detailed measurements of spinal anatomy not possible with standard radiographs. It is not yet known whether there is a threshold beyond which joint moments drive deformity progression
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