The Effect Of Hip Elevation On Acetabular Cup Anteversion In Direct Anterior Approach Total Hip Arthroplasty

Objective:In direct anterior approach(DAA)total hip arthroplasty(THA),most surgeons preoperatively elevate the patient’s hip to facilitate intraoperative exposure to the surgical field.However,whether hip elevation affects the judgment of the position of the prosthesis during surgery and reduces the accuracy of prosthesis implantation is still unclear.This study aimed to judge whether the position of the joint prosthesis changed by analyzing the imaging data of the hip during intraoperative hip elevation and postoperative supine position.We hoped to explore its general change law to provide a reference for clinicians.Materials and Methods:According to the exclusion and inclusion criteria,this study included 62 patients who underwent primary DAA-THA at our joint center from September 2021 to February 2022.All operations were performed by the same surgeon.Before the operation began,the surgeon used a fixed-height wooden hardboard to elevate the patient’s hip.A standard anteroposterior perspective of the pelvis with a C-arm machine was performed during the operation,and the images were preserved.The basic data of the patients on admission,intraoperative blood loss,operation time,ASA score,incision length,and other information were collected.The main evaluation indexes included intraoperative and postoperative acetabular cup anteversion angle,acetabular cup abduction angle,and leg length discrepancy(LLD).Results:1.The Pearson’s correlation coefficient of the acetabular cup anteversion angle calculated by the "Lewinnek" method and the "gold standard" CT method was 0.959(95% CI: 0.9319–0.9749),and the results measured by the two methods were in high agreement.2.The acetabular cup anteversion angle was 16.8±3.2° when the hip was elevated during the operation,and the acetabular cup anteversion angle was 22.0±4.9°when the supine position was performed after the operation,and the difference between the two groups was statistically significant(P<0.001).The acetabular cup anteversion angle with hip elevation during the operation was significantly smaller than that in the supine position after the operation(difference: 5.3°,95% CI: 4.3–6.2),requiring a correction factor of 5° or 6° between the two.3.All of the acetabular cups were located in the Lewinnek "safe zone" when the hip was elevated intraoperatively.85.5% of the acetabular cups were located in the safe zone postoperatively,and 14.5% of the acetabular cups were located in the non-safe area and had an anteversion angle greater than 25°.4.The difference in lower extremity length between the operated and non-operated sides was 1.2 mm(95%CI:-6.4–9.6),and the difference was not statistically significant(P = 0.330).Conclusion:In DAA-THA,elevating the patient’s hip before the operation helps to expose the surgical field,but the pelvis may be tilted after the elevation,resulting in a smaller intraoperative acetabular cup anteversion angle than postoperatively.A correct analysis of the pelvic position before surgery is essential for the positioning and placement of the prosthesis.