Objective:To explore the feasibility and clinical efficacy of oblique lateral interbody fusion (OLIF) in the treatment of adjacent segment disease (ASDis).Methods:Retrospective analysis was conducted on the data of 31 patients with ASDis treated by OLIF in four medical centers from June 2015 to December 2018. There were 17 males and 14 females. The average age was (65.7±3.4) years (range, 59 to 75 years). 19 cases received single-segment fixed fusion, 11 cases received double-segment fixed fusion and 1 case received three-segment fixed fusion. Original fixed fusion site: 1 case of L 1, 2, 3 cases of L 3, 4, 11 cases of L 4, 5, 4 cases of L 5S 1, 6 cases of L 3-L 5, 5 cases of L 4-S 1, and 1 case of L 3-S 1. The time from the initial fixation and fusion to this admission was 82.5±45.5 months (rang, 24 to 180 months). ASDis occurred at the proximal end of the fixed fusion segment in 28 cases and at the distal end in 3 cases. The types of ASDis: degenerative disc disease in 11 cases, lumbar spinal stenosis in 15 cases, degenerative spondylolisthesis in 2 cases, and degenerative scoliosis in 3 cases. The location of ASDis: 6 cases of L 2, 3, 12 cases of L 3, 4, 6 cases of L 4, 5, 3 cases of L 1-L 3, 1 case of L 2-L 4, and 3 cases of L 1-L 4. At admission, 3 cases of lumbar internal fixation had been removed and 28 cases of internal fixation remained. Stand-alone OLIF was performed in 19 cases, OLIF combined with pedicle screw fixation in 8 cases, and OLIF combined with cortical screw fixation in 4 cases. Visual analogue scale (VAS) and Oswestry disability index (ODI) were used to evaluate the low back pain and lumbar function before operation and at the last follow-up, and the imaging results and complications were observed. Results:All patients were followed up. The follow-up time was 23.6±9.6 months (range, 12 to 60 months). The operation time was 73.8±25.3 mins (range, 40 to 180 min), and the intraoperative blood loss was 86.2±67.4 ml (range, 20 to 310 ml). The average blood loss in each segment was 24.8 ml. During the operation, there were 1 case of segmental vein injury, 7 cases of endplate injury, 2 cases of transient iliopsoas muscle weakness, 1 case of thigh pain and numbness, and 1 case of incomplete intestinal obstruction. There was no incision necrosis and infection. The VAS score of low back pain decreased from 5.9±1.9 before operation to 1.4±0.6 at the last follow-up, with a statistically significant difference ( t=8.47, P<0.001). The ODI index recovered from 45.2%±5.7% before operation to 13.8%±4.7% at the last follow-up, with a statistically significant difference ( t=7.92, P<0.001). The height of intervertebral space increased from 8.7±1.6 mm before operation to 11.4±1.9 mm after operation and 9.9±1.8 mm at the last follow-up. There was a statistically significant difference between postoperative and preoperative height of intervertebral space ( F=4.15, P=0.007). There was a statistically significant difference between the last follow-up and postoperative height of intervertebral space ( P=0.011). During the follow-up, there were 13 cases of fusion cage subsidence, 1 case of fusion cage displacement, and no case of internal fixation loosening or fracture. The intervertebral fusion rate was 94%(29/31) and the complication rate was 42%(13/31). Conclusion:ASDis is a common complication after lumbar fixation and fusion, and requires surgical treatment. OLIF is a reliable method to treat ASDis as it has advantages of small trauma, high fusion rate and low complication rate.