Restoration and maintenance of segment lordosis in oblique lumbar interbody fusion

PURPOSE: Restoration of the segment lordosis angle (SLA) can effectively reduce the risk of adjacent segment degeneration. This study aimed to perform a comprehensive multifactor analysis of the risk factors affecting restoration and maintenance of the SLA in oblique lumbar interbody fusion (OLIF). METHODS: Seventy-three patients (93 segments) who underwent OLIF with posterior pedicle screw fixation due to lumbar degenerative disease between January 2015 and December 2019 were included. Radiographic parameters including the middle disc height (MDH), segment lordosis angle (SLA), cage center point ratio (CPR), cage subsidence, and L1 CT Hounsfield Unit (HU) were measured. RESULTS: The postoperative SLA increased from 3.5° to 8.7°, and decreased to 6.7° at the last follow-up. Multivariate analysis showed that preoperative SLA, CPR and cage subsidence were significantly correlated with SLA restoration. The significant correlations were between restoration of SLA with pre-operative SLA (r=-0.575, adjusted R2 = 0.323, P < 0.01) and between SLA restoration and CPR (r = 0.526, adjusted R2 = 0.268, P < 0.01). Cage subsidence was found in 12.9% (12/93) of segments and was the main factor affecting SLA loss (4.2 ± 1.0° versus 1.7 ± 2.1°, P < 0.01). Logistic regression analysis showed that CPR < 50%, L1 CT HU < 110 and cage height > preoperative MDH were risk factors for cage subsidence. Cages placed anteriorly (CPR ≥ 50%) showed a large SLA increase and lower incidence of cage subsidence than those placed posteriorly (5.9 ± 3.9° versus 4.2 ± 3.2°, P < 0.05; 1.8% versus 28.9%, P < 0.05, respectively). CONCLUSION: SLA restoration is dependent on preoperative SLA, cage subsidence and cage position in OLIF. Cage position is the key determinant of SLA restoration and placement of the cage at the anterior position (CPR ≥ 50%) can achieve better restoration of the SLA and reduce the incidence of cage subsidence.