| Objective:Proper anteversion of femoral components can lower the rate of impingement,dislocation,and accelerated wear in total hip arthroplasty(THA).There is a great demand of adjusting femoral anteversion among Crowe Ⅳdevelopmental dysplasia of the hip(DDH).This series of studies aimed to,1.assess the operative femoral anteversion during THA and analyze the need of adjusting stem anteversion.2.analyze the discrepancy between stem anteversion and native femoral anteversion measured by different methods,and explore which method can better predict the stem anteversion.3.investigate the application of modular stem(SROM,DePuy Synthes,Warsaw,Indiana,USA)among high dislocated hips,and identify the risk factors of developing intraoperative periprosthetic femoral fracture and nonunion of subtrochanteric osteotomy after surgery.4.determine whether dislocation height can predict the use of subtrochanteric osteotomy in patients with Crowe Ⅳ DDH.5.evaluate the primary stability of anteversion adjustable femoral stem designed by us through finite element(FE)analysis.Methods:The studies were conducted in five aspects.1.A total of 101 patients(126 hips)who underwent cementless THA with a novel goniometer to determine the femoral anteversion were retrospectively included.The operative femoral anteversion was measured during THA.We further divided those hips into three subgroups based on the range of operative femoral anteversion:group 1(<10°),group 2(10°-30°),and group 3(>30°)and compared the differences of their demographic data.Univariate and multivariate analysis were used to identify the influencing factors for the need of neck-adjustable femoral stem.2.A total of 26 patients(39 hips)treated with robot-assisted THA were retrospectively reviewed.A straight,single-wedge,cementless stem(Accolade II,Stryker,Mahwah,New Jersey,USA)was used in all cases.Preoperative femoral anteversion was measured at three levels on computerized tomography(CT)scan from the top to the middle level of femoral neck(Level 1 to Level 3).During THA,the anteversion on cutting surface was measured prior to femoral broaching based on two reference lines,including mid-cortical line and T line(from sinus piriformis to medial mid-cortex).After femoral broaching,stem anteversion was measured based on the femoral neck trial using Mako system(Stryker,Mahwah,New Jersey,USA).3.We conducted a cross-sectional retrospective study on primary THAs for high dislocated hips receiving SROM stem.Risk factors of intraoperative femoral fracture including demographic,surgical,and technical variables were identified by univariate and multivariate analysis.Primary outcome was the incidence of intraoperative femoral fracture and nonunion of subtrochanteric osteotomy.4.We retrospectively included 102 patients affected by unilateral Crowe Ⅳ DDH who underwent primary THA with SROM stem.Sixty-two hips were performed with subtrochanteric osteotomy and 40 without subtrochanteric osteotomy.The predictive values of height of greater trochanter,height of femoral head/neck junction,and distalization of greater trochanter were analyzed using receiver operating characteristic(ROC)curves.5.FE models were developed of two femurs(native femoral anteversion is about 50°)and an anteversion adjustable femoral stem.The femoral stem was placed in reduced anteversion(35° and 20°).The primary stability was assessed by comparing the stem micromotion and periprosthetic stress to thresholds(150 μm and 224 MPa,respectively)above which fibrous tissue formation and bone damage are expected to prevail.Results:1.Mean operative femoral anteversion was 14.21°±11.80°(range,-9°-60°).Patients with femoral anteversion more than 30° were about 10 years younger than others.Femoral anteversion>30° was more common in DDH patients.From the univariate analysis,we can observe that female sex,diagnosis of DDH(compared with osteonecrosis),higher operative femoral anteversion and its value>30°(compared with<10°)are associated with higher rates of using neck-adjustable femoral stem.However,all these factors were no longer considered as independent influencing factors when mixed with other factors.2.Mean femoral neck anteversion(Level 1)was 9.5°±2.6°(range,-16.8～42.5°),while mean stem anteversion measured by Mako system was 19.9°±2.0°(range,-8.0～49.0°).There was a significant difference between stem anteversion and femoral anteversion except at Level 3,with a mean difference of 0.8°±13.6°(P=0.729).With regard to the intraoperative estimation,stem anteversion significantly increased compared to the value based on mid-cortical line,with a mean difference of 8.4°±13.1°(P<0.001).However,the mean value of stem anteversion was a little smaller than that of femoral anteversion measured by reference to T line,but without statistical significance(P=0.156).3.The incidence of intraoperative femoral fracture and postoperative nonunion of subtrochanteric osteotomy was 4.2%and 2.03%,respectively.Based on the results of univariate analysis,height,weight,diagnosis,surgeon’s volume of THA for high dislocated hips with SROM stem,and surgery year were related to the risk of intraoperative femoral fracture.The results of multivariate model indicated that diagnosis of coxa vara was associated with 7.4-fold higher risk of intraoperative femoral fracture,and that of sequelae from childhood hip infection with 6.5-fold higher risk compared with DDH.In contrast to no use of femoral shortening osteotomy,subtrochanteric osteotomy was an independent risk factor for intraoperative femoral fracture(OR=5.568,95%CI:1.373-22.587).Surgeon’s volume was a protective factor,which reduced the risk by approximately 80%when exceeding 50 cases.Five of 8 cases of nonunion had hip infection in childhood or previous femoral corrective osteotomies with hardware retention.4.The ROC curves showed that distalization of greater trochanter had the highest areas under the ROC curve(AUC),at 0.998.This was followed by height of greater trochanter and height of head/neck junction,which had AUCs of 0.937 and 0.935,respectively.The optimal thresholds of these three indicators were 4.84 cm,6.05 cm,and 4.26 cm.5.FE prediction of micromotion and Von Mises stress were all below the thresholds.In all models,the highest stress value on the bone in all models was observed surrounding the distal part of stem,and the lowest stress value was observed at the lesser trochanter.Conclusions:1.Identification of abnormal operative femoral anteversion could assist in adjusting stem anteversion.2.The middle level of femoral neck on CT scan and T line on cutting surface are better references to measure femoral anteversion for predicting postoperative stem anteversion.However,there was no constant relationship between stem anteversion and predictive value.3.Intraoperative periprosthetic femoral fracture and nonunion of subtrochanteric osteotomy are rare events.Identifying significant factors can help patients and surgeons to better understand the risk of these complications in high dislocated hips.4.Dislocation height is useful in predicting the use of subtrochanteric osteotomy during THA for Crowe Ⅳ DDH.5.Both femoral anteversion adjustment and adequate primary stability can be achieved by the stem we designed.The results of FE analysis can support further biomechanical tests for the stem. |
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