A comparison of acetabular diameter using direct and indirect measurement.

ABSTRACT

Background: In total hip arthroplasty, it is necessary to evaluate the diameter of the acetabulum as a part of the preoperative planning. However, usually the measurement of the acetabular diameter in the anteroposterior view of the pelvic radiograph gives an inaccurate value. Objective: To determine the accuracy of acetabular diameter measurement from various pelvic radiographs when compared to direct measurement. Methods: The study was performed in 10 cadavers; 5 males and 5 females with a mean age of 69.7 years. 20 hips were studied by taking radiographs at 3 positions anteroposterior, 45° iliac oblique and 45° obturator oblique views. The acetabular diameters were directly measured from the cadaver and in all views of pelvic radiographs. Intraobserver and interobserver reliability of all the methods were evaluated by measuring 3 times by 3 doctors. Results: The mean diameter of the acetabulum measured directly from the cadaver was 46.13± 3.05 mm., while when measured from the pelvic radiographs in anteroposterior, iliac oblique and obturator oblique view was 54.29 ± 3.67, 47.63 ± 2.85, and 57.29 ± 4.34 mm. respectively. The iliac oblique view gave the most accurate value with a magnification of 3.36%, while the magnification in the anteroposterior and the obturator oblique view was 17.81% and 24.30%, respectively. The diameter measured from the iliac oblique view was not statistically different from the direct measurement, while the diameter measured from the anteroposterior and obturator oblique view was statistically different (p < 0.001).The intraobserver and interobserver reliability of the 3 observers showed excellent correlations (p < 0.0001). Conclusion: The iliac oblique view of the pelvic radiograph provided the most accurate value compared with the direct measurement. The iliac oblique view is the best view of the pelvic radiograph used to measure the acetabular diameter for operative planning for hip arthroplasty as a guide to choosing the proper prosthetic size.