Insufficient endplate-bone graft contact is a risk factor for high-grade cage subsidence occurring after lateral lumbar interbody fusion supplemented with lateral plate: An analysis of 121 cases.

BACKGROUND

Lateral lumbar interbody fusion (LLIF) is a minimally invasive fusion technique that can be performed with lateral plate. Insufficient contact between the endplate and bone graft may result in cage subsidence. This study aimed to investigate the potential risk factor for high-grade cage subsidence (HCS) occurring after LLIF supplemented with lateral plate.

METHODS

Between June 2017 and February 2023, 121 patients (48 males, 73 females; mean age 63.0 years; minimum follow-up period 12 months) undergoing LLIF supplemented with lateral plate were retrospectively reviewed. The incidence of HCS was assessed, and patients were categorized into HCS group or non-HCS group based on the occurrence of HCS. A revision surgery of posterior pedicle screw fixation was performed in patients with cage subsidence and complained with intolerable back pain or radicular symptoms. Comparative analyses were performed on demographic characteristics, surgical variables, and parameters related to endplate-bone graft contact between the two groups. Multivariable logistic regression analysis was employed to identify the potential risk factors associated with HCS. The receiver operating characteristic (ROC) analysis was used to calculate the cutoff values for the risk factors. Clinical outcomes were evaluated using Oswestry Disability Index (ODI), and radiographic fusion at the final follow-up was assessed based on the Bridwell grading system.

RESULTS

The HCS group comprised 12 patients, while the non-HCS group included 109 patients. The incidence of HCS occurring after LLIF supplemented with lateral plate was 9.9 %. Compared to non-HCS group, patients in HCS group had lower sagittal and coronal endplate-bone graft contact rates and larger cage-endplate angles. Low sagittal (OR, 1.099; 95 % CI, 1.033-1.169; P=0.003) and low coronal (OR, 1.149, 95 % CI, 1.061-1.243, P=0.001) endplate-bone graft contact rates were determined to be correlated with HCS. The cutoff value of the sagittal and coronal endplate-bone graft contact rate was 63.5 % and 60.9 %. Eleven (91.7 %) patients in HCS group underwent revision posterior pedicle screw fixation. Both HCS and non-HCS groups experienced significant improvements in ODI at the final follow-up, while there were no differences between groups. Ninety-five (87.2 %) patients in non-HCS group, and nine (81.8 %) of the 11 patients who underwent revision surgery in HCS group achieved radiographic fusion at the final follow-up.

CONCLUSIONS

The incidence of HCS occurring after LLIF supplemented with lateral plate was 9.9%. Insufficient endplate-bone graft contact is an important risk factor of HCS, and sagittal and coronal endplate-bone graft contact rates can be used as effective predictors for HCS.