The Influence Of Femoral Anatomic Morphology On Femoral Component Coronal Alignment In Total Knee Arthroplasty

The correct restoration of lower-limp mechanical axis is important to total knee arthroplasty.Postoperative neutral coronal mechanical axis is associated with a minimized risk for implant wear and component loosening.Traditional methods use the fixed distal femur resection angle and intramedullary alignment guide to do femoral resection.However,it could be easily impacted by variable femoral anatomic morphology.Recently many studies supports use the variable distal femur resection angle to reduce the influence of variable femoral anatomic morphology and improve femoral component alignment.Our study analyzed different methods to measure patient special resection angle,and compared two different femoral valgus correction angle on femoral coronal alignment during Total Knee Arthroplasty.Furthermore,we analyzed the influence of femoral anatomic morphology on femoral valgus correction angle.Finally,we use a novel navigation named i Assist to guide the distal femoral and proximal tibial cutting positions,and study the accuracy of this technology.Purposes:1.To study the influence of patient special resection angle on femoral coronal alignment during Total Knee Arthroplasty.2.To study the influence of femoral anatomic morphology on femoral valgus correction angle.3.Compare the radiographic outcomes between the iAssist navigation group and DFMA group.Methods:We retrospectively studied a consecutive series of 111 patients who underwent 137 total knee arthroplasty done by two surgeon from March 2015 to June 2015.One surgeon used the angle between the distal 1/3 femoral anatomic axis and the femoral mechanical axis(“DFMA”group,71 TKA)as femoral valgus correction angle.The other one used the angle between the femoral anatomic axis and the femoral mechanical axis(“FMA”group,66 TKA)as femoral valgus correction angle.All patients received standing AP hip-to-knee radiographs preoperative and postoperative.Compared the angle between the femoral mechanical axis and the distal femoral condylar line of two groups.Secondly,we measuered femoral bowing,neck-shaft angle,offset,HKA angle and demographic factors.Then we analyzed the influence of these factors on femoral valgus correction angle.Finally,we use i Assist navigation to guide the distal femoral and proximal tibial cutting positions,and compare the accuracy of mechanical alignment and positions of the prosthesis between iAssist group and DFMA group.Results:1.There is not different in age,BMI,preoperative deformity,preoperative or postoperative HSS score between two groups,(P=0.149~0.985).The mean femoral valgus correction angle of “DFMA”group is 6.08±1.57°,and the angle of “FMA”group is 4.82±0.74°(P<0.05).2.A total of 76.1% of femoral components in the“DFMA”group and 51.5% in the“FMA”group were within 0 ± 2°(P =005).3.A total of 74.6% of femoral components in the“DFMA”group and 53.0% in the“FMA”group were within 0 ± 3°(P =008).There is not different in the mean HKA alignment between two groups(1.60±2.46°vs 1.98±3.35°,P=0.458).4.Regarding the correlation between the DFMA and the radiographic measurements,only the femoral bow show a good correlation with the DFMA(r=0.876).In patients with a larger lateral femoral bowing,the DFMA had a tendency to increase.DFMA=5.372+0.413×femoral lateral bowing angle(r=0.876,P<0.05).The age and HKA angle demonstrated correlation coefficients to the DFMA,but was poor or low.Femoral neck-shaft angle and offset did not show statistically significant correlation coefficient to the DFMA.5.The use of iAssist navigation resulted in fewer outliers in the femoral component and better femoral alignment.(DFMA group 1.03°±1.75° vs i Assist group 0.34°±1.17°,P<0.05).6.There is no statistically difference in HKA angle between two groups,but iAssist group has fewer outliers(P=0.02).No statistically difference was found between two groups in postoperative tibial component position.Conclusion:1.Use the DFMA as femoral resection angle improves femoral component coronal alignment than FMA.The femoral resection angle of “FMA”group is relatively small which make postoperative coronal alignment more varus.2.There was no statistically significant difference in the mean postoperative 6 months HSS scores between DFMA group and FMA group.3.DFMA was mainly impacted by femoral bowing deformity,multiple stepwise regression analysis demonstrated that DFMA=5.372+0.413×femoral lateral bowing angle(r=0.876,P<0.05).The DFMA had a tendency to increase with a larger lateral femoral bowing.4.The iAssist navigation improves accuracy for femoral alignment and positioning of the prosthesis,but did not work effectively in improves tibial component position.