Radiological evaluation of fusion patterns after lateral lumbar interbody fusion: institutional case series

There is no consensus on how to evaluate segmental fusion after lateral lumbar interbody fusion (LLIF). Bone bridges (BB) between two contiguous vertebra are reported as pathognomonic criteria for anterior fusion. However, to the best of our knowledge, there are no radiological investigations on zygapophyseal joints (ZJ) status after LLIF. The aim of this radiological study was to investigate the different fusion patterns after LLIF.

This is a retrospective single-centre radiological study. Patients who underwent LLIF and posterior percutaneous screw fixation for degenerative spondylolisthesis, on a single lumbar level, were considered for eligibility. Complete radiological data and a minimum follow-up of 1 year were the inclusion criteria. Intervertebral BB were investigated for evaluating anterior fusion and ZJ ankylotic degeneration was evaluated according Pathria et al., as a matter of proof of posterior fusion and segmental immobilization.

Seventy-four patients were finally included in the present study. Twelve months after surgery, intervertebral BB were recognized in 58 segments (78.3%), whereas ZJ Pathria grade was I in 8 (10.8%) patients, II in 15 (20.3%) and III in 51 (68.9%) that were considered posteriorly fused. The overlapping rate between anteriorly and posteriorly fused segments was 72.4% (42 segments), whereas 10 (13.5%) did not achieve any fusion, anterior or posterior, and 6 (8.1%) were posteriorly fused only.

Our results seem to suggest that anterior fusion is not sufficient to achieve segmental immobilization. Further properly designed investigations are needed to investigate eventual clinical-radiological correlations.