INTRODUCTION
Posterior lumbar interbody fusion (PLIF) is a common fusion technique used in indicated lumbar spinal pathologies. Cage migration, though not so common, is one of its dreaded complications because of the challenges with revision surgeries, morbidity, and the financial impact on the patients. There are several documented risk factors for cage migration but will believe they are not yet exhausted.
The aim of this retrospective study was to evaluate risk factors for cage migration following PLIF using interbody cages and suggest solutions to prevent them.
METHODS
We reviewed medical records for patients who had PIF between August 2011 and February 2023 and included those who met the inclusion criteria. Patients were grouped into two groups, those with and without cage migration. Variables of interest were patients age and sex, surgeon, fusion levels, cage shape and material, osteoporosis, spondylolisthesis, segmental lordosis, pre-operative disc height, which is a reflection of the Pfirrmann grade, post-operative disc height measured on first post operative day and the difference between the two heights. Data were analysed using SPPS 24.
RESULTS
We studied 181 patients with 248 PLIF levels. The mean age distribution was 70.49 ± 7.60yrs with a male to female ratio of 1:2.6. Mean follow-up duration and time to cage migration were 2.82±1.99yrs and 30.36±4.51days, respectively. There were 14(5.6%) cases of migration and 10(71.43%) of them had revision surgeries. Univariate logistic regression analysis revealed interbody fusion level (OR 5.14, P-value 0.04), cage material (OR 0.24 P-value 0.01), cage shape (OR 0.02 P-value 0.01) pre-operative disc height (OR 22.33, P-value <0.001) and negative change in post operative disc height (OR 0.01, P-value <0.001) have significant correlation to migration. However, multivariate logistic regression revealed only cage shape (OR 0.02, 95%CI 0.001-0.54; P-value 0.02) and negative change in post-operative disc height (OR 0.02, 95% CI 0.002-0.13; P-value <0.01) were independent risk factors for cage migration.
DISCUSSION
Fusion at L5/S1 level, box cage, peek cage, high pre-operative disc height hence lower Pfirrmann grade and a negative change in post operative disc height correlated with a higher risk of cage migration. However only cage shape (box) and negative change in post-operative disc space were independent risk factors for cage migration.
The tendency to use an undersized cage, with poor snug fit, in larger pre-operative disc space coupled with the routine segmental compression explains why the post operative disc height was reduced instead of the expected increase. This can be verified intra-operatively. Also, cylindrical cage has better endplate anchorage than box cage and this explains while it is less likely to migrate.
Ensuring an increase in post-operative disc height from the pre-operative height and when possible, using other fusion techniques for patients with normal height will reduce the rate of cage migration. In addition, a meticulous endplate preparation and segmental compression technique is advised.