Reliability of a New Radiological Parameter Named the Modified Tönnis Angle for the Evaluation of Acetabular Dysplasia in Adults

To evaluate the reliability of Tönnis angle and modified Tönnis angle on pelvic radiographs in adults.
Patients and Conventional anterior-posterior pelvic radiographs of patients were selected from the picture archiving communication system (PACS) in the department of medical radiology of the Second Hospital of Shandong University. Tönnis angle and modified Tönnis angle were measured. All measurements were performed by two experienced observers who worked independently of each other. These measurements were performed again after one month. They were performed digitally using tools of the PACS. Reliability of Tönnis angle and modified Tönnis angle was assessed by intraclass correlation coefficients and Bland-Altman plot.
A total of 142 patients (79 females and 63 males) with 284 hips were selected. Tönnis angle and modified Tönnis angle were measured on the 284 hips by two observers. Intraclass correlation coefficients (ICCs) for intraobserver agreement of measurements were 0.962 and 0.983 for Tönnis angle, and 0.971 and 0.984 for modified Tönnis angle. ICCs for interobserver agreement of measurements were 0.936 for Tönnis angle and 0.932 for modified Tönnis angle. Bland-Altman plot suggested good interobserver agreement of measurements for Tönnis angle and modified Tönnis angle.
Reliability of Tönnis angle and modified Tönnis angle was good according to ICCs and the Bland-Altman plot.