Objectives:To analyze the impact of the kyphotic apical vertebra(KAV)position on sagittal plane characteristics and quality of life in patients with degenerative kyphosis(DK).Methods:A retrospective analy-sis was conducted on the clinical and imaging data of 68 DK patients hospitalized and treated in the Depart-ment of Orthopedic Surgery,Nanjing Drum Tower Hospital from February 2010 to December 2022.There were 8 males and 60 females,aged 46-76 years old(60.6±6.5 years).The patients were divided into two groups based on the position of the KAV:Group 1(G1)included 38 patients with the KAV at or above L1,and Group 2(G2)included 30 patients with the KAV below L1.The thoracic kyphosis(TK),lumbar lordosis(LL),sagittal vertical axis(SVA),pelvic incidence(PI),pelvic tilt(PT),sacral slope(SS),T1-pelvic angle(TPA),and global kyphosis(GK)were measured on standing full-spine lateral X-rays before operation,and the value of PI-LL was calculated.Health related quality of life(HRQoL)was assessed using the Scoliosis Research So-ciety-22(SRS-22)questionnaire,Oswestry disability index(ODI),visual analog scale(VAS)score,and SF-36 questionnaire.Independent samples t-tests were used to compare sagittal plane parameters and HRQoL scores between the two groups.Pearson correlation analysis was employed to examine the relationship between sagit-tal plane parameters and HRQoL scores.Results:There was no significant difference in the age and sex ra-tios between the two groups(P＞0.05).The GK,LL,TK,SVA,PI,PT,SS,TPA,and PI-LL in G1 group were respectively 61.3°±20.0°,26.9°±18.9°,32.3°±19.0°,53.5±48.1mm,40.4°±13.4°,24.8°±12.6°,17.0°±11.7°,23.0°±13.5°,and 21.6°±15.6°,which in G2 group were 38.8°±16.0°,14.4°±13.7,10.8±9.8°,96.5±67.8mm,44.8°±16.2°,30.1°±10.8°,14.7°±11.5°,32.6°±14.5°,and 33.8°±18.3°.The GK,LL,and TK were significantly greater in G1 group than those in G2 group(P＜0.05),and SVA,TPA,and PI-LL were less in G1 group than those in G2 group(P＜0.05).The VAS score,ODI,SF-36 physical component score(PCS),SF-36 mental com-ponent score(MCS),SRS-22(function,pain,self-image,mental health,subtotal score)in G1 group were 4.2±1.6,(37.9±15.2)％,45.8±11.3,48.6±12.7,and(17.6±4.6,18.6±4.3,17.7±4.5,17.8±4.9,71.7±9.3),which were 5.8±1.7,(48.6±20.0)％,38.2±12.9,44.2±13.1,and(15.6±4.5,16.0±3.6,16.6±4.9,17.1±4.3,65.4±11.1)in G2 group.G1 group was lower in VAS score and ODI significantly(P＜0.05)and higher in SRS-22 subtotal score,SRS-22 pain domain score,and SF-36 PCS significantly(P＜0.05)than G2 group.Pearson correlation analysis showed that SVA was positively correlated with VAS and ODI in both groups(G1 group:r=0.437,P=0.006 and r=0.356,P=0.028;G2 group:r=0.405,P=0.027 and r=0.408,P=0.025),while negatively correlated with SF-36 PCS(G1 group:r=-0.365,P=0.024;G2 group:r=-0.410,P=0.024).TPA was positively correlated with VAS score in both groups(G1 group:r=0.343,P=0.035;G2 group:r=0.369,P=0.045).In G2 group,SVA neg-atively correlated with SRS-22 subtotal score(r=-0.391,P=0.033),and PI-LL was positively correlated with VAS score(r=0.390,P=0.033).Conclusions:The position of KAV affects the pelvic-spinal sagittal alignment obviously in DK patients,and the patients with KAV located below L1 level have significantly higher SVA,TPA,and PI-LL compared to the patients whose KAV located at or above L1 level,which is significantly associated with decreased quality of life.