A Simple And Convent Method To Improve The Accuracy Of Preoperative Templating Of Total Hip Arthroplasty

PURPOSE:To eliminate the bad effects of magnification of digital radiograph and improve the accuracy of preoperative templating of THA,we applicate a new stepwise method which combine the traditional acetate with standing digital radiograph calibrated by scaling ball.METHODS:We retrospectively studied preoperative and postoperative bilateral hips digital radiographs and implants data of82patients (42men and40women with a mean age of51.2years, range21-77years). All the radiograph was taken with standing position, placing a50-mm-diameter scaling ball between the legs as near as possible by supporting with a rod. Total109primary uncemented THAs(left57hips, right52hips)performed in all the82patients (55patients with Unilateral,27patients with Bilateral,)from January and September in2014. Calibrate the scale of the50-mm-diameter scaling ball in the digital radiograph on the computer screen by matching it with self-design different diameter circle acetate with corresponding magnification. Then two investigators use traditional acetate provided by manufacture to template the size of implants for THA, comparing with the true size. For Double-blind test, the two investigators didn’t get additional information except the data of implant brand and sides of operative hips during the templating. RESULTS:Compared with true implant size, templating predicted cup size correctly within two sizes in98.17%, within one size in92.67%and right size in50.50%of all cases. Prediction of Stem Size within two sizes in99.08%,within1size in85.32%and right size in56.00%of all cases. Leg Length Discrepancy (LLD) within10mm in56.3%, within20mm in87.2%for all the bilateral THA, and within10mm in89.0%, within20mm in98.1%for all the unilateral THA. Offset Discrepancy within10mm in76.4%, within20mm in98.2%for all the unilateral THA.CONCLUSION:With the self-design magnification calibration acetate on digital radiograph, we have got high accuracy preoperative planning of prosthesis sizes(acetabular cup and femoral stem). The results of LLD and offset are also satisfied.There is no dislocation case in the follow-up. The preoperative design and the matching of prosthesisis are the basis to achieve suitable mechanical conduction in Total hip arthroplasty, and they are the keys for long-term stability of the joints. Accurate preoperative designed can reduce the risk of intraoperative and postoperative periprosthetic fracture, dislocation, loosening and early abnormal wear. This study can provide more accurate information for the preoperative planning, lower preoperative design errors, reduce surgery time,and reduce the incidence of postoperative complication. Another advantage of this study is that it can be applied to different brands traditional templates. As the traditional templates from different brand have different scales, this study makes it impossible to be more accurate while using different traditional templates to do the preoperative planning. Furthermore, metal balls and calibration templates are easy to get. We can do the preoperative planning with any electronic products and review X-ray films anywhere which brings great convenience. No need for any additional equipment, professional computer software or additional costs, especially suitable for underdeveloped regions.