Inter and Intra-Observer Reliability of Dorr Classification in Proximal Femur Morphology

Proximal femur morphology determines the choice of cemented or uncemented Total Hip Arthroplasty (THR), and Dorr classification is widely used to type this characteristic. As a result, a considerable reliability for such typing system is expected.
The current study aimed at assessing inter and intra-observer reliability of Dorr classification in proximal femur morphology.
A total of 50 standard hip radiographs from patients with trauma or THR candidates were evaluated by 6 observers, including 2 senior orthopedic residents, 2 orthopedic surgeons, and 2 hip fellowship-trained orthopedic surgeons, using the Dorr classification system. Subsequently, radiographs were re-numbered and re-evaluated, 6 weeks after the first review. Cohen’s Kappa statistic was used for statistical analysis of inter and intra-observer reliability.
The mean intra-observer and inter-observer kappa value for the residents was 0.560 and 0.592, respectively. The mean intra-observer and inter-observer kappa value for the orthopedists was 0.566 and 0.540, respectively. The mean intra-observer and inter-observer kappa value for the hip fellowships was 0.477 and 0.490, respectively.
A minimum to moderate inter and intra-observer reliability of Dorr classification system was seen between the observers of the current study. These results suggest that the classification of the femur morphology is more challenging than previously described and characterization of a single Dorr type, especially in case of uncertainty between type B and C of Dorr might need reconsideration, in order to prevent its adverse effect on the patients’ outcome.