Analysis of factors impacting inter-body fusion cage subsidence following an oblique lateral interbody fusion (OLIF) stand-alone procedure

Background Lumbar oblique lateral interbody fusion (OLIF stand-alone) procedures have become a common treatment for various spinal conditions, including spinal stenosis and spondylolisthesis. However, cage subsidence following OLIF stand-alone procedures is a significant concern that can compromise the surgical outcomes. Objective To investigate the occurrence of cage subsidence following OLIF procedures and identify the relevant factors influencing cage subsidence. Method A retrospective analysis was conducted on 86 patients who underwent elective OLIF stand-alone procedures at the Affiliated People's Hospital of Qingdao University between 2019 and 2023. Patients were categorized into two groups based on disc height (DH) subsidence: cage non-subsidence group (< 2 mm) and cage subsidence group (> 2 mm). General and imaging data were collected pre-surgery, post-surgery, and at six months follow-up. Single-factor analysis identified factors influencing cage subsidence, followed by multi-factor regression analysis on these variables to determine their impact. Results When the degree of DH subsidence in the last follow-up (M6) was evaluated, among the 86 patients (102 segments), 26 patients (25.49%) fulfilled the criteria for cage subsidence. Factors with clinical and statistical significance in the single-factor analysis were incorporated into the multi-factor analysis, and it was found that the mean CT value of the concerned segment, multifidus area, and severe multifidus atrophy were relevant risk factors for cage subsidence; the protective factors for cage subsidence were degree III zygapophyseal joint degeneration, posterior cage position, and end-plate inflammation sclerosis (P < 0.05). Conclusion Surgeons should be cautious in preoperatively identifying patients at risk of cage subsidence, particularly those with a low mean CT value of the concerned segment or severe multifidus atrophy. During surgery, selecting a cage of adequate length to span the epiphyseal ring and align with the original DH can help protect paravertebral muscles from iatrogenic injury and reduce the risk of cage subsidence.