Assessing Cobb Angle Agreement in Community Spine Radiographs: Clinical Significance in Adolescent Idiopathic Scoliosis Patients

Primary care physicians rely on community radiology reports to confirm an Adolescent Idiopathic Scoliosis (AIS) diagnosis prior to spine specialist referral. Accurate reporting of spine x-rays is essential as results guide management. While Cobb angle is known to have excellent reliability, this may be over-reported, specific to orthopaedic specialists and with some studies pre-determining end-vertebrae. The study objectives were 1) to determine the agreement of Cobb angle readings between index evaluation of community spine x-ray and re-evaluation of the same image by tertiary-care clinicians (spine specialist and pediatric radiologist) and 2) to determine if inaccurate measurements were associated with late AIS referrals, defined as those who present as likely surgical candidates on initial presentation. A review of AIS patients (n=170) seen for an initial visit at a tertiary-care pediatric hospital between January-September 2021 was conducted, excluding those seen for second opinion, missing index Cobb angle or with index imaging from the same institution. Community index spine x-rays available on the institution's PACS (n=119) were independently measured by two blinded raters (spine specialist and pediatric radiologist). The agreement in Cobb angle readings between community radiology and tertiary-care clinicians was measured using intraclass correlation coefficient (ICC) and the agreement in the corresponding Scoliosis Research Society management categories was measured using Fleiss’ Kappa statistic (κ). Agreement statistics were calculated for evaluation of the reference standard 3-foot standing spine x-ray in the same cohort. Bland-Altman plots were constructed to compare raters on index image and reference standard. Logistic regression was used to estimate the odds of late referrals from the discrepancy in Cobb angle measurements between community radiology and reference standard when images were within 90 days (n=111). Discrepancies were defined as differences in Cobb angle measurements >5°. An adjusted model included age, imaging location, image quality and referring specialty. Most index x-rays (72.6%) were obtained at a private community clinic. The agreement in Cobb angle on the index x-ray between community radiologist and spine specialist was fair (ICC=0.78 95% CI 0.66-0.86, SEM=6.14°) with moderate agreement in corresponding management (κ=0.58). On the same image, the agreement between community radiologist and pediatric radiologist remains fair (ICC=0.74 95% CI 0.65-0.81, SEM=6.73°) though improved agreement in corresponding management (κ=0.65). Comparatively, the agreement between spine specialist and pediatric radiologist on both index and reference standard was excellent (ICC=0.96, 95% CI 0.89-0.98, SEM=2.57°; ICC=0.97, 95% CI 0.95-0.98, SEM=2.86°) with substantial agreement in corresponding management (κ=0.73; κ=0.71). The proportion of patients with discrepancies in Cobb angle measurements was 45.0% when comparing those with index images within 90 days of the reference standard. The proportion of patients who present late was 34.2%. The odds of late referral increased when there were inaccuracies in community measurements (OR = 3.55 95% CI 1.91-6.59). There are clinically important differences between community radiology and tertiary-care evaluation of spine x-rays. Inaccurate interpretation impacts timely referrals, contributing to missed opportunities for conservative treatment and increased surgical burden.