Radiographic assessment of the subtalar joint: An evaluation of the Kellgren-Lawrence scale and proposal of a novel scale

Abstract Objective To evaluate the reliability of grading subtalar (ST) arthrosis on lateral weightbearing radiographs in a heterogenous patient population using the Kellgren-Lawrence (KL) scale, correlate these findings to advanced imaging (CT and/or MRI), and to validate a novel scale. Materials and methods A random collection of 40 lateral weightbearing radiographs presenting to a foot and ankle clinic were reviewed by nine multi-disciplinary independent reviewers. Interobserver reliability was assessed for KL scores. A musculoskeletal radiologist graded available advanced imaging on all 40 radiographs and the advanced imaging scores were correlated to the radiographic scores. A novel scoring system was created and tested for interobserver reliability. Results There was overall fair reliability amongst reviewers with the traditional KL score, kappa = 0.26. The best agreement was seen amongst those deemed to have a grade 0, with only moderate agreement (k = 0.50). There was only fair interobserver reliability with severe, Grade 4 scores (k = 0.28). Radiographic scores did have moderate correlation with advanced imaging (r = 0.56). A new, simple grading system was proposed and its interobserver reliability was improved substantially (kappa =0.68). Conclusions The KL scoring system is not applicable to the subtalar joint. The new NSS grading system has improved reliability. Radiographs only had moderate correlation to advanced imaging. Further studies are warranted to correlate clinically.