Comparison of distribution, agreement and correlation between the original and modified Merle d'Aubigné-Postel Score and the Harris Hip Score after acetabular fracture treatment: Moderate agreement, high ceiling effect and excellent correlation in 450 patients

Background In acetabular fracture treatment, 3 disease-specific outcome scores are mainly used: the original and modified Merle d'Aubigné-Postel Score, and the Harris Hip Score. Methods The original and modified Merle d'Aubigné-Postel Score and the Harris Hip Score were recorded in 1,153 follow-ups of 450 patients. 492 follow-ups were excluded because factors other than the acetabular fracture were found to affect the outcome scores. This gave 661 patient records for the study. Results The Spearman correlations were between 0.81 and 0.89. The quartile analyses showed Kappa agreement between 0.45 and 0.55. About 40% of the observations were classified into another quartile when switching from one outcome score to another. The 25th and 50th percentiles comprised 85% and 95% of the total numeric scores, respectively, while the 75th percentiles showed ceiling value (100% of the maximum) in all 3 scores. Interpretation Despite the excellent overall correlation between the outcome scores, the Kappa agreements were only moderate. The scores were all skewed in distribution with considerable ceiling effects that could limit their clinical use. The scores did not capture any differences in 25% of the observations at the upper end of the scales.