Effects Of Hip Rotation Center And Femoral Offset Reconstruction On The Leg Length Discrepancy After Total Hip Arthroplasty In Patients With Hip Osteoarthritis

Objective: To disscuss the relationship among the hip rotation center height,the difference of the femoral offset and the difference of the length of the lower limbs after total hip arthroplasty in patients with hip osteoarthritis.Methods: 102 patients with hip osteoarthritis in our hospital from January 2014 to October 2016 operated unilateral total hip arthroplasty,including 39 wemen,63 men;left hip were 41 cases,right hip were 61 cases;age ranged from 39 to 79 years old,with the average year is 62.4.Among them there were 14 cases of avascular necrosis of the femoral head with secondary hip osteoarthritis,26 cases of Developmental Dysplasia of Hip with secondary hip osteoarthritis and 62 cases of primary hip osteoarthritis.All patients on standard pelvis anteroposterior X-ray picture,measured the bilateral lower extremity length difference(the difference from the small peak trochanter to the bilateral tear-drop line' vertical distance),hip rotation center height(the vertical distance from the center of the hip rotation to the same side teardrop),femoral offset(the vertical distance between hip rotation center from the long axis of the femoral shaft.),and the difference of two-sides femoral offset,combined with preoperative templating knowing the ipsilateral acetabular and femoral medullary cavity size in order to estimation the possible use of intraoperative prosthesis type.In the same way all postoperative patients in 1 week were measured on standard pelvis anteroposterior X-ray picture,including the leg length discreprancy,the vertical distance between the hip center rotation from the ipsilateral teardrop,the femoral offset of the hip prosthesis and the discrepancy of two-sides hip offsets.The standard of femoral offset' reconstruction was the difference of the two-sides femoral offset lees than 4mm,and the standard of LLD was two-sides lower extremity differennce less than 5mm.Using methods to statistically analyze the data that we mentioned above,in order to know how the hip rotation center height and the reconstruction of femoral offset affected the limb length in patients with hip osteoarthritis after total hip arthroplasty.Result: 102 cases of patients with preoperative low extremity difference measurement: bilateral limbs length were equal(less than 5mm)30 cases(29.4%);unequal(difference more than 5mm)72 cases(70.6%),all cases showed ipsilateral limb shortening,including the leg length discrepancy of 24 cases between 6~ 10 mm,48 cases of leg length discrepancy are more than 10 mm.We mmeasured the lower limb length difference with all patients in a week after operation: isometric(the lower limb'difference is less than 5mm)were 48 cases(47.1%),among them 14 cases of postoperative lower limb length were completely isometric,34 cases were between 1~5mm,while there are 54 cases(52.9%)whose lower limb length were more than 5mm,which included 41 cases between 6~10mm,while 13 cases of lower limb length were more than 10 mm.The lower limb length difference of the mean and standard deviation was 11.96±10.03 mm preoperatively,and the same parameter was 6.42± 5.82 mm after the surgery,and the results were proved statistically significant by the paired t test,with t=5.297,P < 0.01.The femoral offset' mean and standard deviation: preoperative contralateral postoperative side was 39.77±6.71 mm,affected side postoperative was 40.84±5.61mm;by paired t test analysising,with t=-1.549,P=0.125,the difference was without statistically significant.The hip rotation centre height of mean and standard deviation: preoperative contralateral was 26.37 ± 7.85 mm,affected postoperative side was 30.39±6.03 mm,using paired t test analysis,with t=-5.138,P<0.01,the difference was proved statistically significant.The difference of bilateral femoral offset' mean and standard deviation was 7.65±5.36 mm before the surgery,and 4.99±3.89 mm after the surgery,using the paired t test,with t=4.292,P<0.01 the difference was proved statistically significant.The variance analysis showed that among different groups of the postoperative lower limb length changes with the bilateral femoral offest difference,F=17.77,P<0.01,the difference was statistically significant,the rotation center height,F=18.23,P < 0.01,the difference was statistically significant.There was a negative correlation between the height of the hip rotation center and the difference of the lower limbs length(R=-0.294,P<0.01).The difference of the femoral offset between the two groups was positive correlation with the lower limbs length(R=0.471,P<0.01).Conclusions:1.The lower limb shortening exist in patients with unilateral osteoarthritis of the hip before the THA.2.Hip rotation center height and the reconstruction of femoral offset are the related factors that affected the LLD with hip osteoarthritis after total hip arthroplasty,hip rotation center height and the lower limb length differences are negative,while the postoperative bilateral femoral eccentricity and postoperative lower limb length discrepancy was positively correlated.3.Preoperative X-ray measurement of limb length differences of patients,using the template measuring and evaluating the prosthesis type size and placement,the prosthesis tryout and good femoral eccentricity and rotation center of hip joint reconstruction are effective methods for prevention of hip osteoarthritis after total hip arthroplasty leg length.