Fusion rates of a morselized local bone graft in polyetheretherketone cages in posterior lumbar interbody fusion by quantitative analysis using consecutive three-dimensional computed tomography scans

Background contextPosterior lumbar interbody fusion (PLIF) using harvested local bone inserted into a polyetheretherketone (PEEK) cage is a commonly used procedure, but the accurate fusion rate of a cage, cage to bone contact area ratio, and the changes in fusion rate with time after surgery are unknown.PurposeThe aim was to conduct a quantitative analysis of the fusion rates and the cage to bone contact area ratios at each period of time using a PEEK cage in PLIF using a consecutive three-dimensional (3D) computed tomography (CT) scan.Study designThis was a prospective study using a consecutive 3D thin-section CT scan.Patient sampleThirty patients aged between 37 and 73 years set to undergo elective PLIF with PEEK cages and pedicle screw fixation were included in the study.Outcome measuresThe assessments included the Korean Oswestry Disability Index (K-ODI), Short Form (SF)-36 questionnaire, Visual Analog Scale (VAS) pain score, and dynamic plane radiographs, preoperatively and at 6 and 12 months after surgery.MethodsThree-dimensional CT scans were performed at 6 and 12 months after surgery. Three-dimensional CT assessments of the following were performed: fusion rate of the cage, cage to bone contact area ratio, and fusion rate of the interbody bone graft besides the cage.ResultsThe 6-month fusion rate of the segment was 86.7%, which increased to 90.0% at 12 months. The fusion area ratio between the cage area and end plate showed a significant increase from 52.0% at 6 months to 58.5% at 12 months. Regarding the fusion area ratio between the cage and end plate, the ratio between the lower surface of the cage was significantly higher than that of the upper surface. In addition, the K-ODI, SF-36, and VAS values were similar at 6 and 12 months after surgery.ConclusionsThe fusion rate of the PEEK cage used in PLIF measured at 12 months was higher than that measured at 6 months. Therefore, an assessment on the complete fusion of local bone at 12 months after surgery is more accurate.