Degenerative Lumbar Scoliosis

Abstract

Study Design. A radiographic review of 78 consecutive patients with degenerative rotatory lumbar scoliosis. Objective. To assess the correlation between rotary olisthesis and neural canal dimensions using radiographic indexes and to establish a gradation system of lateral rotatory olisthesis. Summary of Background Data. Degenerative scoliosis is a three-dimensional deformity often associated with spinal stenosis, although the association is not well defined. Methods. A total of 78 consecutive patients (average age, 69 years) with de novo degenerative scoliosis (79% lumbar, 21% thoracolumbar; average curve, 25°) were studied with plain radiographs and MRI at presentation. Radiographic measurements included lateral translation, anteroposterior olisthesis, 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 cross-sectional area bilaterally (convexity and concavity). Measurements were conducted twice on each lumbar level (total, 312) and the average was recorded. Results. Lateral translation 5 mm or less (Grade I) was associated with Nash-Moe change 0 (23%) or I (77%), lateral translation 6–10 mm (Grade II) was coupled with Nash-Moe change 0 (20%) or I (80%) and lateral deviation more than 11 mm (Grade III) was associated with I (76%) or II (24%) Nash-Moe change. Maximum intervertebral rotation tended to be at either L2–L3 (48%) or L3–L4 (39%). Increased lateral translation was associated with increased intervertebral rotation (r = 0.37, P < 0.001). Increased anteroposterior olisthesis was associated with decreased anteroposterior diameter (r = −0.18, P < 0.001) and cross-sectional area (r = −0.11, P < 0.05) of the dural sac. Larger segmental Cobb angles were associated with greater foraminal cross-sectional area in the convexity (r = 0.12, P < 0.05). In the concavity, there was no significant correlation (P > 0.05) between indexes of rotary olisthesis and foraminal area or subarticular height. Cross-sectional foraminal area and subarticular height were significantly larger in the convexity than in the concavity of the scoliotic levels. Conclusions. In degenerative scoliotic curves, lateral translation is associated with rotation. Increased rotary olisthesis does not lead to decreased dural sac area. Anteroposterior olisthesis is inversely correlated to the dural sac anteroposterior diameter and cross-sectional area. With increased segmental Cobb angle, foraminal cross-sectional area enlarges in the convexity and does 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.