Abstract
BackgroundCross-table lateral (CL) radiography is a convenient and feasible method to assess cup version angle (VA) after total hip arthroplasty; However, pelvic tilt (PT) may contribute to its measurement inaccuracy. How PT affects CL radiographic measurements have not been well studied. We sought (1) to determine the effect of the PT on cup version measurement on CL radiography and (2) to develop a method for reducing measurement errors caused by the PT.MethodsWe used 3D technique to construct standard model and capture CL radiography simulation. A linear regression model was created to analyze the relationship between PT and VA. CL radiography and computed tomography (CT) were performed for the enrolled patients after surgery. The consistency between CL and CT measurements were verified by intra-class correlation coefficient (ICC).ResultsThere was a high correlation between the VA and PT. For each 1-degree increased in the PT, the VA decreased by 0.76° (R2 = 0.995, p < 0.001). Based on the data, we created a corrective formula to convert the radiographic measurements into values approximating the actual VA under a natural pelvic position. The VA measurements corrected by our equation was in high agreement with the CT-measured values with reference to the corresponding PT (ICC = 0.988, p < 0.001), which was in sharp contrast to that without PT control (ICC = 0.454, p = 0.203).ConclusionsThe PT may contribute to cup version measurement inaccuracies on CL radiography. Our mathematical algorithm can serve as a reliable method to improve the accuracy of CL radiography.
Highlights
Cross-table lateral (CL) radiography is a convenient and feasible method to assess cup version angle (VA) after total hip arthroplasty; pelvic tilt (PT) may contribute to its measurement inaccuracy
Repeatability All intra-observer and inter-observer intra-class correlation coefficient (ICC) were excellent for the measurements of the PT obtained from the additional lateral radiographs and VA obtained from the CL radiographs, 3D-simulated CL radiographs, and Computed tomography (CT) scans (Table 1)
Our correction approach can effectively improve the accuracy of CL radiography when measuring the VA
Summary
Cross-table lateral (CL) radiography is a convenient and feasible method to assess cup version angle (VA) after total hip arthroplasty; pelvic tilt (PT) may contribute to its measurement inaccuracy. CL radiography may be a more convenient and feasible method than AP radiography, in which cup version can be directly measured and anteversion and retroversion can be discriminated from each other [9, 10]. It may provide acceptable assessment of acetabular component position, it is not reliable enough for precise measurement [10,11,12]. The extent to which the PT affects CL radiographic measurements and how to compensate for this effect have not been well studied
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