Knee Varus Deformity And Selection Of The Positioning Reference Point For Proximal Tibial In TKA

Objective: In order to improve the accuracy of tibial prosthesis placement and alignment with tibial extramedullary locating guide in total knee arthroplasty,the proximal tibial varus deformity was measured and analyzed on preoperative full-length X-ray films of lower extremities under weight-bearing.It was suggested that the proximal tibial reference point should be shifted laterally when TKA was applied to the knee joint with proximal tibial varus deformity.The alignment of tibial prosthesis can achieve better accuracy and restore the ideal alignment of lower limb force line.Methods:(1)211 valid cases were collected and 252 TKA were performed.The full-length X-ray images of the lower limbs were evaluated and analyzed before and after operation.The following parameters were measured: HKA,MAD,mMPTA,JLCA,FVA,TVA,PVA,as well as general data and functional prognosis related data.Statistical methods were used to analyze the data and explore the intrinsic relationship among the parameters.(2)Linear regression analysis was used to evaluate the relationship between tibial varus(TVA,PVA)and MAD;Spearman rank correlation was used to calculate the correlation coefficients between expected varus angle and TVA,PVA,and R square and P values;and post HKA tibial varus(MAD,TVA,PVA)was used to plot the ROC curve,specifying the cutoff value of tibial varus.Cut-off value was used to predict abnormal HKA after operation.Results:(1)The incidence of tibial varus deformity was 81.7%,the average TVA was(1.13±0.42)°,the average PVA was(4.71±3.51)°,and the average MAD was(4.68±4.26)mm.Among the three variables(TVA,PVA,MAD)describing the degree of tibial proximal varus deformity,PVA had the most positive correlation with the expected tibial varus angle,r= 0.319,which could be used for the proximal tibial varus process.There is a positive correlation between PVA and MAD.The linear regression equation between MAD and PVA is as follows: MAD = 2.66 + 0.51 * PVA.(2)When PVA > 3.5° or MAD > 2.64 mm,it can be used to predict the abnormality of HKA after operation.TVA has no statistical significance in predicting the abnormality of HKA after operation.(3)With PVA=0° as the normal group,PVA≠0° as the proximal tibial varus deformity group as the grouping standard,HKA in the normal group was(2.13 +2.17)° after operation,and the abnormal value of HKA in the normal group was 9 cases,accounting for 19.6% of the normal group;HKA in the tibial varus deformity group was(2.9 +2.75)° after operation,and the abnormal value of HKA in the reorganized group was 65 cases,accounting for 31.6% of the reorganized cases.The difference between the two groups was statistically significant(t=-2.437,p=0.015).There were 2 cases of abnormal MPTA after operation in the normal group,accounting for 4.3% of the normal group,and 29 cases of abnormal MPTA after operation in the tibial varus deformity group,accounting for 14.1% of the cases.There was no significant difference between the two groups.The ROM of tibial varus deformity group was(104.62±7.73)° after operation,and that of normal group was(111.17±10.67)°.There was no significant difference in VAS pain score between the two groups.(4)The larger the PVA,the more likely the HKA to be uncorrected,r = 0.172.Conclusion: A large proportion of Chinese patients with knee osteoarthritis receiving TKA have inherent joint varus deformity in the proximal tibia.Preoperative full-length X-ray examination of lower extremities in weight-bearing position should be improved,and PVA should be used as a routine method for measuring tibial varus deformity to individualize the lateral distance of proximal tibial reference points.When PVA is less than 3 degrees,the locating point of extramedullary guided locator should be shifted to the lateral side by about 3 mm routinely;when PVA is more than 4 degrees,it should be shifted to the lateral side by at least 4 mm.Patients with varus deformity of the knee joint should be carefully operated.If the degree of tibial varus deformity is very obvious,TKA assisted by computer navigation can be recommended.