The effect of scoliotic deformity on spine kinematics in adolescents

Background: While adolescent idiopathic scoliosis (AIS) produces well characterized deformation in spinal form, the effect on spinal function, namely mobility, is not well known. Better understanding of scoliotic spinal mobility could yield better treatment targets and diagnoses. The purpose of this study was to characterize the spinal mobility differences due to AIS. It was hypothesized that the AIS group would exhibit reduced mobility compared to the typical adolescent (TA) group.

Methods: Eleven adolescents with right thoracic AIS, apices T6-T10, and eleven age- and gender-matched TAs moved to their maximum bent position in sagittal and coronal plane bending tasks. A Trakstar (Ascension Technologies Burlington, VT) was used to collect position data. The study was approved by the local IRB. Using MATLAB (MathWorks, Natick, MA) normalized segmental angles were calculated for upper thoracic (UT) from T1-T3, mid thoracic (MT) from T3-T6, lower thoracic (LT) from T6-T10, thoracolumbar (TL) from T10-L1, upper lumbar (UL) from L1-L3, and thoracic from T1-L1 by subtracting the standing position from the maximum bent position and dividing by number of motion units in each segment. Mann Whitney tests (α = 0.05) were used to determine mobility differences.

Results: The findings indicated that the AIS group had comparatively increased mobility in the periapical regions of the spine. The AIS group had an increase of 1.2° in the mid thoracic region (p = 0.01) during flexion, an increase of 1.0° in the mid thoracic region (p = 0.01), 1.5° in the thoracolumbar region (p = 0.02), and 0.7° in thoracic region (p = 0.04) during left anterior-lateral flexion, an increase of 6.0° in the upper lumbar region (p = 0.02) during right anterior-lateral flexion, and an increase of 2.2° in the upper lumbar region during left lateral bending (p < 0.01).

Conclusions: Participants with AIS did not have reduced mobility in sagittal or coronal motion. Contrarily, the AIS group often had a greater mobility, especially in segments directly above and below the apex. This indicates the scoliotic spine is flexible and may compensate near the apex.