Study design:

A retrospective comparative study with radiographic measurements.

Objective:

To investigate incidences and risk factors of screw-related superior facet articular surface violation (FASV) and optimal pedicle screw angles (PSAs) to avoid FASV at L4 and L5 levels in transforaminal lumbar interbody fusion (TLIF) with either open surgery (OS) or minimal invasive (MIS) techniques with 3D C-arm navigation.

Summary of background data:

L4 to S1 are common levels in TLIF. Adjacent segment diseases (ASD) following TLIF is not uncommon. Screw-related FASV at the superior level is one of the potential risk factors for ASD.

Methods:

In the OS and MIS groups, 111 and 110 screws were included at L4 level, and 114 and 110 screws at L5 level, respectively. Post-operative computed tomography examined screw-related FASV at L3-4 and L4-5 facet levels. The entry point was the location where pedicle screws placed into the facet joints.

Results:

The OS technique and insertion at the L5 level increased the likelihood of FASV 2.56 and 1.81 times, respectively. Multivariate logistic regressions analysis determined PSA was a significant factor associated with FASV. Pearson’s r between PSA and the distance between midline and entry point was 0.905 (p < .0001). Adding one degree of convergence in PSA led to a mean 0.87 lower odds of an FASV event, regardless of surgical techniques. In 90% of patients in the OS and MIS groups, PSA with FASV was <11.9° and <15.9° at L4 level, and <15.9° and <21.8° at L5 level, respectively.

Conclusion:

PSAs played an important role in FASV. MIS allowed greater PSAs and resulted in fewer incidences of FASV. To avoid FASV in 90% of patients, the PSAs might be at least 11.9° and 15.9° at L4 level; and 15.9° and 21.8° at L5 level for OS and MIS techniques, respectively.Level of Evidence: 3.