Experimental Research About The Measurement Of Acetabular Anteversion On The Radiograph After THA

Background:The measurement of acetabular component anteversion on the radiograph after THA is important both to evaluate the intraoperative position of acetabular cup and postoperative follow-up. Many formulas are proposed to measure the acetabular anteversion on the radiograph, but there are some problems as follows:1)The definitions of acetabular anteversion were used indiscriminately;2)Abuse of formulas:The usable conditions of formulas had not be noticed;3)The stability,repeatability and accuracy of these formulas in clinical use is uncertain.Objective:To discuss the relationship between OA and RA;To test the stability, repeatability and accuracy of these formulas used in clinical (In this papers 5 formulas were grouped into two categories).Material and Mehtods:We selected four specimens of adult pelvis and kept the plane of radiation from the PAP 100cm. When Pl is 30°,45°,60°, adjusted OA to 0°,10°,20°,30°,40°respectively, took the plain anteroposterior radiographs projection when the PAP in different tilt position (horizontal, anterior pelvic tilt 10°,posterior pelvic tilt 10°) and under different projection center (acetabular center, pelvic center, the same-side of the ipsilateral anterior superior iliac spine, pubic symphysis). We use computer software under the same magnification to measure s,1, h, v, ssd, RI and get the radiographic anteversion(RAM and RAL) by Mclaren and Liaw formula.Results:1) Compared the stability and repeatability of two types of formulas in practical application:In different groups of RI and OA, the range of RAM was 15.2-18.5°and the standard deviation was 4.97-6.21. The range of RAL was 1.6-2.6°and the standard deviation was 0.52-0.77. Anterior (posterior) pelvic tilt and projection center affects RAm significantly(p<0.01). There were not significant differences (p>0.05)between the average of RALand RAL (when anterior pelvic tilt 10°,or posterior pelvic tilt 10°,or projection center at pelvic center, or at the same-side of the ipsilateral anterior superior iliac spine, or at pubic symphysis).2) Compared two types of formula and the real RA.Standard RAM compared with the real RA, the difference was 0.08±0.47 (P=0.196).When PAP is parallel with coronal plate of human body and the projection center focus on acetabular center, there was not difference between the real RA and RAM. RAL compared with the real RA,the difference was 7.37±2.02 (P<0.01).When RI=30°, RAL-RA:9.72±0.55(P<0.01); When RI=30°,RAL-RA:7.48±0.71 (P<0.01);When RI=30°,RAL-RA:4.91±0.62 (P<0.01).There was significant difference between the real RA and RAL.The difference decreased with the RI increased.3) Compared RAL'and the real RA.RAL'=RAL+(RI/6-15°).RAL' compared with the real RA, the difference was 0.11±0.64 (P>0.05). There was no significant difference between the real RA and RAL'.Conclusion:1) Under the standard condition, the accuracy of Mclaren formula which represented the first kind of formulas was high. Affected by pelvic tilt and the projection center, the stability and repeatability of the first kind of formulas were low.2) under experimental conditions, pelvic tilt and the projection center affected Liaw formula which represented the second kind of formulas not significantly. So the stability and repeatability of the Liaw formula was high. But it's accuracy was low.3) under experimental conditions, the formula of Arcsin had high stability, repeatability, accuracy. But it's usable condition needs to be further confirmed.