Do Radiographic Results of Transforaminal Lumbar Interbody Fusion Vary with Cage Position in Patients with Degenerative Lumbar Diseases?

Objective To investigate whether the radiographic results are affected by cage position in single‐level transforaminal lumbar interbody fusion (TLIF). Method Between January 2016 and June 2018, 130 patients (62 males and 68 females, average age: 55.28 ± 10.11 years) who underwent single‐level TLIF were analyzed retrospectively. Standing lateral radiographs of the lumbar spine were collected and evaluated preoperatively, postoperatively, and at the time of last follow‐up. Cage position in the fused segment was recorded using a central point ratio (CPR), which indicated the cage position. CPR is calculated by dividing the distance between the cage center point and the posterior extent of the superior endplate of the inferior vertebra by the length of the superior endplate of the inferior vertebra. Based on cage positions, the patients were divided into three groups: Anterior Group (n = 38); Middle Group (n = 68); and Posterior Group (n = 24). Segmental lumbar lordosis (SLL), foraminal height (FH), posterior disc height (PDH), and anterior disc height (ADH) were evaluated. A subanalysis was also performed on cage height within each group. Results The average follow‐up time of the patients was 35.20 ± 4.43 months. The mean values of CPR in Anterior Group, Middle Group, and Posterior Group were 0.64, 0.51, and 0.37, respectively. The FH, PDH, and ADH were significantly increased after TLIF in all groups (P