Inter- and intraobserver reliability of the Mayo coronoid-centric classification for proximal ulna fracture-dislocations

Proximal ulna fracture-dislocations are challenging injuries with variable patterns of elbow instability. Accurate identification of the affected structures and classification of the injury are essential for guiding treatment. The Mayo Clinic coronoid-centric classification organizes these injuries based on the continuity of the coronoid process with major ulnar fragments, placing the coronoid process at the center of the classification criteria. This study assessed the external validity of this classification using an independent cohort of patients with proximal ulna fracture-dislocations. We retrospectively analyzed 79 consecutive patients with proximal ulna fracture-dislocations treated at our institution over a 15-year period. Eligible cases involved bicortical proximal ulna fractures with associated elbow or proximal radioulnar joint dislocation, confirmed on anteroposterior and lateral radiographs and computed tomography scans. Exclusion criteria included prior surgery or fracture in the region, pathological fractures, incomplete imaging studies, or surgery performed by any evaluator to minimize recall bias. Six orthopedic surgeons, 3 with less than 5 years and 3 with more than 15 years of experience in upper extremity surgery, classified all cases in 2 rounds separated by eight weeks. None of them had prior exposure to the classification system. Patterns were categorized as transolecranon, Monteggia variant, or transulnar, according to the Mayo Clinic coronoid-centric classification. Interobserver and intraobserver agreements were calculated, both with 95% confidence intervals (CIs) estimated using case-based bootstrapping. A prior sample size calculation was performed with an expected interobserver kappa of 0.77. Transolecranon fractures were the most frequent (n = 32), followed by Monteggia variant fractures (n = 28) and transulnar fractures (n = 19). Transolecranon patterns predominated in older patients and low-energy trauma injuries, whereas Monteggia variants and transulnar fractures were associated with younger age and high-energy mechanisms. Interobserver agreement was substantial in both rounds (κ = 0.73; 95% CI, 0.64-0.80 and κ = 0.75; 95% CI, 0.66-0.82). Less experienced surgeons showed a slightly higher agreement (κ = 0.76; 95% CI, 0.66-0.85 and κ = 0.73; 95% CI, 0.62-0.83) than more experienced surgeons (κ = 0.67; 95% CI, 0.55-0.77 and κ = 0.75; 95% CI, 0.64-0.85). Mean intraobserver agreement was also substantial (κ = 0.77; 95% CI, 0.71-0.83), without significant subgroup differences. The Mayo Clinic coronoid-centric classification demonstrated substantial reproducibility when applied by surgeons without prior exposure, using only 2D imaging. Further multicenter studies correlating subtypes with functional outcomes are warranted to assess its prognostic value and role in surgical planning.