Radiographic Cobb Angle: A Feature of Congenital Lumbar Spine Stenosis

A low cost, reproducible radiographic method of diagnosing congenital lumbar spinal stenosis (CLSS) is lacking. We hypothesized that the Cobb angle for lumbar lordosis would be smaller in patients with CLSS, based on observations in our spine clinic patient population. Here, we compared lumbar lordosis Cobb angles with the radiographic ratio method in patients with normal spine imaging, degenerative spinal stenosis, and with CLSS.

Orthopedic surgeons categorized patients with low back pain as "Normal," "Degenerative spinal stenosis," and "CLSS" based on clinical presentation and findings on lumbar magnetic resonance imaging. We included 30 patients from each cohort who had undergone lateral lumbar spine radiographs and lumbar magnetic resonance imaging. For each lateral radiograph, 2 measurement methods were used (1) 4-line lumbosacral Cobb angle between L2-S1 and (2) the ratio of the anteroposterior vertebral body diameter and spinal canal anteroposterior diameter at the L3 level. We performed logistic regression analyses of CLSS prediction by Cobb angle vs the ratio method in all three cohorts. Covariates included age, gender, and body mass index.

The radiographic Cobb angles were smaller in CLSS patients when compared to the degenerative disease and normal cohorts: a smaller radiographic Cobb angle showed higher odds ratio (OR) of predicting CLSS diagnosis compared to the radiographic ratio when compared with degenerative disease (OR = 0.28; 95% CI: 0.11-0.78, P = 0.01) and when compared with the normal cohort (OR = 0.46; 95% CI: 0.24-0.92, P = 0.03). Radiographic ratio measurements showed no difference between the three cohorts (P = 0.12). CLSS was associated with male gender (P = 0.04), younger age (P = 0.01), and higher body mass index (P = 0.01).

The radiographic Cobb angle method for lumbar lordosis may be useful for raising the possibility of CLSS as the diagnosis.