Abstract
The aim of this study was to evaluate the limitations of the Tönnis angle as one of the most commonly used parameters in the diagnosis of acetabular dysplasia, and to explore the feasibility of the modified Tönnis angle in the diagnosis of acetabular dysplasia. A total of 224 patients (120 females and 104 males) with 448 hips, aged between 15 and 83 years (median, 45.0 years), were selected for the measurement of the center-edge (CE) and Tönnis angles. To evaluate the relative position of the medial edge of the acetabular sourcil, a new parameter, known as the center-medial-edge (CME) angle, was designed. As an improvement of the Tönnis angle, a new angle preliminarily termed the modified Tönnis angle was created. In addition, the degree of clarity of the medial edge of the acetabular sourcil on radiograph was evaluated, and the hips were divided into the clear-edge and blurred-edge groups. The hips belonging to the blurred-edge group could not be used for Tönnis angle measurements. All measurements were performed digitally using the tool of the picture-archiving communication system. Among the 448 acetabular sourcils, 142 had a blurred medial edge (31.7%). The mean value of the CME angle was 37.94°, with a range of 21.76–63.99°. The 95% prediction interval of the modified Tönnis angle was estimated to be −6.39 to 11.73°. The correlation coefficients were −0.838 between the CE and Tönnis angles, 0.889 between the Tönnis and modified Tönnis angles and −0.905 between the CE and modified Tönnis angles. In conclusion, the modified Tönnis angle can substitute for the Tönnis angle without joint space narrowing and subluxation of the hip, particularly when the Tönnis angle cannot be measured due to a blurred medial edge of the acetabular sourcil on pelvic radiograph.
Highlights
Acetabular dysplasia is a relatively common abnormality of the anatomy of the acetabulum, whose prevalence in adults varies across studies from 1-15% [1,2,3,4]
All 448 hips were used for CE and modified Tönnis angle measurement
The mean modified Tönnis angle was 2.67 ̊ (n=448; 95% confidence intervals (CI), 2.24‐3.10 ̊; standard deviation, 4.62), with the 95% prediction interval being estimated to be -6.39 to 11.73 ̊
Summary
Acetabular dysplasia is a relatively common abnormality of the anatomy of the acetabulum, whose prevalence in adults varies across studies from 1-15% [1,2,3,4]. Dysfunction, pain and limpness are the initial symptoms of acetabular dysplasia in adults [5]. Adults with acetabular dysplasia usually have a shallow or deformed acetabulum, occasionally with luxation or subluxation of the hip [7]. Patients with persistent acetabular dysplasia and subluxation are at high risk of osteoarthritis (OA) [8,9]. The lack of early diagnosis and treatment for acetabular dysplasia can lead to OA in adults [10]. The imaging diagnosis of acetabular dysplasia typically depends on radiographic evaluation. Certain parameters, such as the center‐edge (CE) and Tönnis angles, are the most commonly used measurements of acetabular dysplasia [7,11,12]
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