A novel radiological classification of the distal humerus: morphometric analysis across two European populations

Total elbow arthroplasty (TEA) utilization is projected to increase substantially, with revision TEA expected to outnumber primary procedures by 2050. Aseptic loosening remains the most common indication for TEA revision. This study aimed to develop and validate a novel morphometric classification system for the distal humerus to optimize pre-operative planning and implant selection.

A retrospective analysis of 300 anteroposterior elbow radiographs from patients in Spain (n = 138) and Germany (n = 162) was conducted. The morphometric index was calculated as the ratio of medullary canal widths at 120 mm and 35 mm from the lateral epicondyle. Methodology follows the validated percentile-based approach introduced by Citak et al, adapted here to the context of distal humeral morphology. Percentile-based classification thresholds were established: type A (≤25th percentile, ≤0.239), type B (25th-75th percentile, 0.239-0.336), and type C (>75th percentile, >0.336). Interobserver and intraobserver reliability were assessed. Statistical analyses included analysis of variance (ANOVA), t-tests, and chi-square tests to evaluate morphometric differences across demographic groups.

The morphometric index ranged from 0.134 to 0.523 (mean 0.29 ± 0.07). Classification yielded type A: 75 cases (25%), type B: 150 cases (50%), and type C: 75 cases (25%). Interobserver reliability was excellent (r = 0.873, P < .001), with outstanding intraobserver reproducibility (r > 0.97). Significant geographical differences were observed, with Spanish patients exhibiting higher morphometric indices than German patients (0.317 ± 0.071 vs. 0.266 ± 0.060, t = 6.747, P < .001) and greater type C prevalence (38.4% vs. 13.6%, χ² = 31.508, P < .001). Females demonstrated significantly higher indices than males (0.322 ± 0.068 vs. 0.268 ± 0.063, t = -7.009, P < .001), with type A being male-dominant (86.7%) and type C female-dominant (62.7%). Patients over 65 years showed a higher prevalence of type C morphology (33.3%).

This novel morphometric classification system demonstrates excellent reliability and reveals significant population-based and sex-related variations in distal humeral anatomy. These findings support the clinical relevance of population-specific morphometric considerations in TEA planning and implant design.