Enhancing Consistency in Posterior Malleolus Fracture Classification: A Comprehensive Interobserver Reliability Study With 20 Raters Using the Mason & Molloy Classification

Introduction: Over the past decade, there has been a growing interest in the identification and treatment of posterior malleolus fragments, driven by a better understanding of their significance. The Mason & Molloy (M&M) classification system has emerged as a valuable tool for systematically categorizing these fractures and assisting clinicians in formulating treatment. We aim to assess the interobserver reliability of the M&M classification for posterior malleolus fracture by using 20 raters. Methodology: The study was conducted at a major foot and ankle referral center in Wythenshawe, Manchester, UK. Thirty-eight Computed Tomography (CT) scans were evaluated by 20 independent raters: 15 general orthopedic and trauma surgeons plus five foot and ankle surgeons. Each rater classified the posterior malleolus fracture according to M&M classification into type 1, 2A, 2B, 3, or not classifiable. Statistical analysis was done with the R software package and SPSS (v26; IBM Corp., Armonk, NY). Fleiss kappa (kappa) coefficient with a 95% confidence interval (CI) was applied. Results: The interobserver agreement was moderate with a global kappa value of 0.531 (95% CI: 0.518, 0.544). There were good agreements for identifying type 3 M&M (kappa=0.785) and those that are not applicable for M&M classification (kappa=0.785). There was a strong correlation between all raters in using M&M classification (Tb=0.53-0.59) except for Rater 12. Conclusion: M&M classification remains a valuable tool to guide the management of patients with these subsets of ankle fractures.