Objective To explore the feasibility and clinical efficacy of modified transforaminal lumbar interbody fusion for the treatment of lumbar spinal stenosis with lumbar instability in the elderly.Methods Retrospective study was done on 45 elderly patients diagnosed as lumbar spinal stenosis with lumbar instability treated by modified transforaminal lumbar interbody fusion from June 2011 to December 2012.There were 25 males and 20 females aged from 65 to 78 years [mean (70.64.0) years].The operation time,blood loss,and complications were recorded and analyzed.The visual analog scale (VAS) score,and Japanese Orthopaedic Association (JOA) score were used to assess clinical outcomes before and 3 months after treatment and at the last follow-up.According to the criteria of Brantigan-Steffe,intervertebral fusion was evaluated.Results The operation of 45 patients was successful,and there were no severe complication.The average operative time was (126 23) min,(range,100～ 185 min),and the average amount of blood loss was (272±89) ml (range,180-550 ml).There was no injury of nerve root,dural tear,or deep infection.All patients were followed up for 12 months to 30 months with an average of (20.6±5.8) months.The VAS score of low back pain was decreased from (4.8 ± 1.7) before operation to (1.6 ± 0.5) at 3 months after operation and (1.3±0.3) at last follow-up.The VAS score of leg pain was decreased from (6.7±1.6) before operation to (1.2±0.5) at 3 months after operation and (0.6±0.3) at last follow-up.The JOA score was increased from (13.2±4.9) before operation to (23.8±4.0) at 3 months after operation and (24.1 4.2) at last follow-up.There were significant differences in the VAS score and JOA score between pre-and post-operation (F=68.35,98.58,89.73,all P＜0.05),but no significant difference between 3 months after operation and final follow-up (all P ＞ 0.05).We observed no pedicle screw loosening,breaking,orany pullingout of intervertebral fusion cage.All patients showed evidence of fusion in each operated segment according to the criteria of BrantiganSteffe.Conclusions Modified transforaminal lumbar interbody fusion has the advantages including less invasion,sufficient decompression,and less interference to neural structures,and it may provide an ideal surgical method for lumbar spinal stenosis with lumbar instability in the elderly.