Radiographic Evaluation of BFX Acetabular Component Position in Dogs

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Objective:To assess the reliability of radiographic measurement of angle of lateral opening (ALO) and angle of version of BFX acetabular cups.Study Design:In vitro radiographic study.Sample Population:BFX cups (24, 28, and 32 mm).Methods:Total hip replacement constructs (cups, 17 mm femoral head and a #7 CFX stem) were mounted on an inclinometer. Ventrodorsal radiographs were obtained with ALO varying between 21° and 70° and inclination set at 0°, 10°, 20°, and 30°. Radiographs were randomized using a random sequence generator. Three observers blinded to the radiograph order assessed ALO using 3 methods: (1) an ellipse method based on trigonometry; (2) using a measurement from the center of the femoral head to the truncated surface of the cup; (3) by visual estimation using a reference chart. Version was measured by assessing the ventral edge of the truncated surface.Results:ALO methods 2 and 3 were accurate and precise to within 10° and were significantly more accurate and precise than method 1 (P<.001). All methods were significantly less accurate with increasing inclination. Version measurement was accurate and precise to within 7° with 0–20° of inclination, but significantly less accurate with 30° of inclination.Conclusions:Methods 2 and 3, but not method 1, were sufficiently accurate and precise to be clinically useful. Version measurement was clinically useful when inclination was ≤20°.

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