Objective:To evaluate the efficacy of modified femoral neck osteotomy(mFNO)in the surgical treatment of patients with ankylosing spondylitis(AS)and severe spinal kyphosis combined with hip flexion contracture.Methods:A retrospective analysis was conducted on 61 AS patients(103 hips)with spinal kyphosis and hip flexion contracture who underwent pedicle subtraction osteotomy(PSO)and total hip arthroplasty(THA)from January 1,2019 to November 15,2023.Data on mFNO operation time,blood loss,preoperative and postoperative values of the angle of the trunk and lower limb(ATL),hip passive range of motion(ROM),visual analogue scale(VAS),and incidence of in-hospital compli-cations were recorded.Statistical analysis was performed using paired-samples t test.P＜0.05 was con-sidered statistically significant.Results:The study ultimately included 10 cases,9 males and 1 female,with an average age of(41.30±9.03)years.These patients underwent surgery for a total of 52 times,including 19 hips both receiving mFNO and THA,and 14 times PSO.The average operation time for nine bilateral mFNO was(133.11±34.81)min,with blood loss of(433.33±187.10)mL.A unilateral mFNO took 60 min with 200 mL of blood loss.The preoperative ATL of 19 hips was 40.37°±13.66°,and the postoperative ATL value was 88.47°±12.46°(P＜0.05).The preoperative VAS score was 0,while the postoperative VAS score was 5.95±1.51(P＜0.05).The preoperative hip extension ROM was 37.37°±18.13°,while the postoperative hip extension ROM was-4.95°±21.24°(P＜0.05).Hip flexion ROM improved from 37.37°±18.13° to 50.79°±20.36° after FNO(P＜0.05).There were three cases of in-hospital complications(3/52,5.67％):One case of postoperative atelectasis fol-lowing PSO(1/52,1.92％),one greater trochanter fracture identified during THA(1/52,1.92％),and one early dislocation post-THA(1/52,1.92％).Conclusion:mFNO significantly improves the ATL in AS patients with severe spinal kyphosis combined with hip flexion contracture,facilitating PSO and THA surgeries.