Risk factors for cage subsidence and clinical outcomes after transforaminal and posterior lumbar interbody fusion

Background Cage subsidence is a very common complication after lumbar interbody fusion. It may compromise vertebral interbody fusion through progressive spinal deformity and consequently cause compression of neural elements. Clinical relevance remains, however, unclear, with few studies on this subject and even less information regarding its correlation with clinical findings. The aim of this study was to identify risk factors for cage subsidence and clinical evaluation after transforaminal (TLIF) and posterior (PLIF) lumbar interbody fusion. Methods A retrospective study in patients submitted to TLIF and PLIF between 2008 and 2017 was conducted. Results A total of 165 patients were included (123 TLIF and 42 PLIF). Univariate analysis showed an increased risk of cage subsidence in spondylolisthesis comparing with degenerative disk disease ( p = 0.007). A higher preoperative lumbar lordosis angle ( p = 0.014) and cage placement in L2-L3 ( p = 0.012) were associated with higher risk of subsidence. The posterior cage positioning on vertebral endplate was associated with a higher risk of subsidence ( p = 0.028) and significant subsidence ( p = 0.005), defined as cage migration > 50% of cage height. PLIF presented a higher risk when comparing with TLIF ( p = 0.024). Hounsfield unit (HU) values