Objective To investigate the effect of different lower extremity force lines after initial total knee arthroplasty(TKA)on the early clinical outcomes of patients with varus knee osteoarthritis(KOA).Methods Fifty-five patients(73 knees)with KOA who underwent TKA at the First Affiliated Hospital of Xinxiang Medical University from October 2018 to March 2022 were selected as research subjects.According to the postoperative hip-knee-ankle angle(HKA),the patients were divided into the valgus alignment group(HKA＜-3°,4 knees),neutral alignment group(-3°≤HKA ≤3°,32 knees),mild varus alignment group(3°＜HKA＜6°,30 knees),and severe varus alignment group(HKA ≥6°,7 knees).The mechanical lateral distal femoral angle(mLDFA),mechanical medial proximal tibial angle(mMPTA),range of motion(ROM)of knees,and joint line convergence angle(JLCA)of the four groups of patients were measured before and 1 week after surgery.The Hospital for Special Surgery Knee Scores(HSS),The Western Ontario and McMaster Universities Osteoarthritis Index(WOMAC)scores,and numeric rating scale(NRS)scores of the knee joints of patients in the four groups were also recorded preoperatively and 6 months postoperatively.Results The overall postoperative mLDFA,mMPTA,ROM and HSS scores were significantly greater than the preoperative values and the JLCA,WOMAC and NRS scores were significantly less than the preoperative values in 55 patients(73 knees)(P＜0.01).There was no statistically significant difference in the preoperative mLDFA,mMPTA,JLCA and ROM among the patients in the four groups(F=2.689,0.692,0.476,0.892;P＞0.05).Postoperative mLDFA,mMPTA,and ROM were significantly greater than preoperative values and JLCA was significantly less than preoperative value in patients in the neutral alignment,mild varus alignment,and severe varus groups(P＜0.05).Postoperative mMPTA and ROM were significantly greater than preoperative values and JLCA was significantly less than preoperative value in patients in the valgus group(P＜0.05);the difference was not statistically significant when compared with preoperative and postoperative mLDFA in patients in the valgus group(P＞0.05).There was no statistically significant difference in the postoperative JLCA and ROM among the four groups(F=1.164,1.045;P＞0.05).The difference in postoperative mLDFA and mMPTA was statistically significant among the four groups(F=21.068,4.551;P＜0.05);the mLDFA of patients in the neutral alignment,mild varus alignment,and severe varus alignment groups was significantly greater than that of the valgus alignment group,and patients in the mild varus alignment and severe varus alignment groups had greater mLDFA than those in the neutral alignment group,patients in the severe varus alignment group had greater mLDFA than those in the mild varus alignment group(P＜0.05);the mMPTA of patients in the neutral alignment,mild varus alignment,and severe varus alignment groups was less than that of patients in the valgus alignment group(P＜0.05);there was no statistically significant difference in the mMPTA among patients in the neutral alignment,mild varus alignment and severe varus alignment groups(P＞0.05).There was no statistically significant difference in the preoperative HSS,WOMAC and NRS scores among the four groups(F/x2=0.141,1.587,3.811;P＞0.05).Postoperative HSS scores were significantly higher and WOMAC and NRS scores were significantly lower than preoperative scores in all groups(P＜0.05).The difference between the postoperative HSS and WOMAC scores of patients in the four groups was statistically significant(F=6.216,7.632;P＜0.05).The postoperative HSS scores of patients in the neutral alignment group and the mild varus alignment group were significantly higher than those of the valgus alignment group and the severe varus alignment group(P＜0.05);the difference in the postoperative HSS scores of patients in the neutral alignment group compared with those of patients in the mild varus alignment group was not statistically significant(P＞0.05);and the difference in the postoperative HSS scores of patients in the valgus alignment group compared with those of patients in the severe varus alignment group was not statistically significant(P＞0.05).The postoperative WOMAC scores of patients in the valgus alignment,mild varus alignment and severe varus alignment groups were significantly higher than those in the neutral alignment group,and the postoperative WOMAC scores of patients in the valgus alignment and severe varus alignment groups were significantly higher than those of patients in the mild varus alignment group(P＜0.05);the difference in postoperative WOMAC scores of patients in the valgus alignment group compared with those in the severe varus alignment group was not statistically significant(P＞0.05).There was no statistically significant difference in the postoperative NRS scores among the four groups(P＞0.05).Conclusion The lower extremity force line in a neutral position after TKA has the best early clinical outcome for patients with preoperative varus KOA,and the lower extremity force line should be reconstructed to a neutral level during TKA.