PLIF is performed commonly nowadays due to the high prevalence of degenerative spinal conditions.Removing the disk material and cartilaginous end plates from the involved intervertebral disk space and filling up the void with a spacer maintaing disk height and to decompress the neural foraminain the anterior and middle spinal columns will increase the chance for bony fusion.Several types of cages are available as ex. polyetheretherketone (PEEK).CT provides a sensitiveThe aim of this study was to evaluate the fusion of double level PLIF using PEEK cages by computed tomographyFusion assessment:We evaluated the bone fusion at least one year post surgery. Multislice CT scans were done for all patients . Classification of interbody fusion success was evaluated according to criteria based on Brantigan, Steffee, and Fraser (BSF) criteria: BSF-1:Radiographic pseudoarthrosis (non-union) is indicated by: collapse of the construct , loss of disc height,vertebral slip, broken screws,displacement of the cage, significant resorption of the bone graft, lucency visible around the periphery of the graft or cage.b) BSF-2:Radiographic locked pseudoarthrosis (questionable fusion) is indicated by lucency visible in the middle of the cage with solid bone growing into the cage from each vertebral endplate.c) BSF-3:Radiographic fusion is indicated by bone bridges at least half of the fusion area with at least the density originally achieved at surgery.

. assessment of interbody fusion.