Preoperative Measurement To Estimate Stem Anteversion In DDH Patients After Primary Cementless Total Hip Arthroplasty

OBJECTIVEAccording to the principle of uncemented stem design,by comparing the femoral anteversion in different CT plane with stem anteversion,we can found the method of measurement to estimate stem anteversion.METHODSThis study includes 31 hips in 23 DDH patients who underwent primary cementless THA between January 2013 and December 2015 in The Ninth People’s Hospital Affiliated to Shang hai Jiaotong University.Preoperative and postoperative CT scans were taken on all patients.The femoral anteversion angle was defined as the angle between the midcortical line and the posterior condylar axis.Five levels were measured.Four levels of center of the lesser trochanter(CLT)(Level 1),the distance from the top of greater trochanter to CLT marked as D,1/4D above CLT(Level 2),1/2D above CLT(Level 3),below femoral head(Level 4).The section of femoral neck using Mimics like the osteotomy in the simulation was signed as Level 5.The midcortical line of the anterior cortical at Level 1 and the posterior cortical at Level 5 was defined as femoral anteversion at Level 1&5.The stem anteversion angle as the angle formed by the stem neck major axis and the posterior aspect of the femoral condylar line.We also measured cup anteversion and the sagittal stem tilt.We calculate the difference value and correlation coefficients between each femoral anteversion and stem anteversion.RESULTSThe femoral anteversion at Level 1 was 35.77°±6.85°(26.38°～47.88°),the femoral anteversion at Level 2 was 28.18°±8.61°(12.56°～45.07°),the femoral anteversion at Level 3 was 21.34°±10.31°(2.29°～44.46°),the femoral anteversion at Level 4 was 17.08°±11.42°(-12.97°～40.14°),the femoral anteversion at Level 5 was 10.81°±11.18°(-16.02°±33.97°),the femoral anteversion at Level 1&5 was 22.08°±10.24°(5.54°～48.51°).The stem anteversion was 21.85°±10.68°(7.40°～43.65°),the sagittal stem tilt was 1.10°±1.46°(-0.76°～5.78°),the cup anteversion was 19.68°±9.52°(1.37°～37.79°),the combined anteversion was 41.53°±14.25°(18.17°～73.23°).The pearson correlation coefficient between femoral anteversion at Level 1.Level 2.Level 3.Level 4.Level 5.Level 1&5 and stem anteversion was 0.722,0.826,0.867,0.777,0.777,0.931,respectively.CONCLUSIONGSThe femoral anteversion at Level 5 is smaller than stem anteversion,the two were significantly different.Femoral anteversion at Level 3 and femoral anteversion at Level 1&5 have a highly positive correlation with stem anteversion,but it is more difficult to measure femoral anteversion at Level 1&5,so we can use femoral anteversion at Level 3 as a substitute of stem anteversion before the THA.