Study design: Retrospective cohort study.
Objective: The objective of the study was to analyze segmental balance in patients with isthmic spondylolisthesis undergoing single-level transforaminal lumbar interbody fusion (TLIF).
Summary of background data: Sagittal malalignment of the fused segment was suggested to be associated with degeneration of the adjacent segment. Meticulous surgical technique and particular attention to hardware positioning with the aim to restore segmental balance at the fusion level have been recommended to achieve better long-term clinical outcomes, but no single study addressed all proposed factors.
Methods: Standard lateral radiographs of the lumbosacral spine in the neutral standing position were retrospectively obtained for 32 patients undergoing single-level TLIF. Preoperative versus postoperative versus final follow-up (12 to 60 mo) values of translational slip (TS), posterior disc space height (PDSH), and segmental lordosis (SL) were compared using paired samples t test. Change in SL postoperatively between groups of next grouping variables: type and position of the interbody device, and rod contouring, was compared using 2-tailed independent samples t test. Association between position of the interbody device and immediate PDSH was addressed with regression analysis postoperatively and at final follow-up.
Results: Mean TS decreased (P<0.001) and mean PDSH increased (P=0.002), but no significant change in SL occurred postoperatively (P=0.811). Increase in SL was observed with ventral positioning of the interbody device (P=0.009) and with bending of connecting rods (P=0.023). During follow-up, there was increase in TS (P=0.002) and decrease in PDSH (P<0.001) and SL (P<0.001) compared with postoperative values. Lower PDSH was found to be associated with more ventral positioning of the interbody device, both postoperatively (P=0.035) and at final follow-up (P=0.029).
Conclusions: This study demonstrates that reduction of TS and restoration of disc space height are readily achieved with single-level TLIF. However, to establish an increase in SL consistent rod contouring and meticulous anterior placement of the interbody device should be applied. Excessive ventral positioning of the cages might result in insufficient disc space height restoration.