Measurement of Acetabular Cup Anteversion with the Circle Theorem
Arkaphat Kosiyatrakul MD*, Suriya Luenam MD*, Thanainit Chotanaphuti MD*
Affiliation : * Department of Orthopaedics, Phramongkutklao Hospital and College of Medicine, Bangkok, Thailand
Objective : Malposition of the acetabular cup is the major risk factor of dislocation after total hip arthroplasty.
Postoperatively, measuring of acetabular cup anteversion is very difficult. The new method for measuring
acetabular cup anteversion on the plain radiograph of the hip with one of the circle theorems in the basic
geometry was created.
Material and Method: An all-polyethylene acetabular cup with known angle of radiographic anteversion
was mouthed to the pelvic bone. Antero-posterior hip and pelvis radiographs were taken with the cup in
randomly 15 different angles of anteversion. These were reviewed by 3 orthopedic residents. All data from 3
observers were collected and examined for the accuracy, inter-observers reliability and intra-observer
reliability of this method. Two films (AP radiograph of the hip and the pelvis) method was used for distinguish
between anteversion and retroversion.
Results : The measurements of radiographic anteversion have the accuracy of plus or minus 2 degrees. The
reliability coefficients of inter-observer variation in the first and second measurements for all definitions of
anteversion are high. Pair t-test showed no significant different between value of the first and the second
measurements for all definitions in all observers. The intra- and inter-observer variations were 3 degrees or
less for all definitions.
Conclusion : The Acetabular cup anteversion measurement using the circle theorem iseasily to perform with
high accuracy and consistency for all definitions of cup anteversion.
Keywords : Measurement, Acetabular cup, Anteversion, Total hip arthroplasty
