Degenerative Adult Scoliosis: Radiographic Correlation of Lateral Rotary Listhesis with Neural Canal Dimensions

Background: Degenerative scoliosis is a three-dimensional deformity often associated with spinal stenosis, although the relationship is not well-defined.

Objective: To assess the correlation between rotary listhesis and neural canal dimensions using radiographic indices.

Methods: 43 consecutive patients (average age 69) with de novo degenerative scoliosis (72% lumbar, 28% thoracolumbar; average curve 25°) were studied with plain radiographs and MRI at presentation. Radiographic measurements included lateral translation, anteroposterior listhesis, Cobb angle and intervertebral rotation (Nash-Moe grade difference). Computerized measurements of MRI included dural sac cross-sectional area and anteroposterior diameter; minimum subarticular height and foramen crosssectional area bilaterally (convexity and concavity). Measurements were conducted twice on each lumbar segment and the average was recorded.

Results: Maximum intervertebral rotation tended to be at either L2-3 (44%) or L3-4 (44%). Increased intervertebral rotation was associated with increased lateral translation (r=0.33, p0.05) between indices of rotary listhesis and foraminal area or subarticular height. No significant difference was detected in neural canal dimensions of segments with (group I, n=107) and without (group II, n=65) rotational changes.

Conclusions: In degenerative scoliotic curves, lateral translation is the result of rotation. Increased rotary listhesis does not lead to decreased dural sac area. With increased rotary listhesis, lateral canal dimensions enlarge in the convexity and do not decrease in the concavity. Presence of intervertebral rotation alone does not appear to be associated with reduced neural canal dimensions. Ligamentum flavum hypertrophy, posterior disc bulging and bony overgrowth are more likely to contribute to stenosis irrespective of scoliosis.