The Impact of Interbody Location on Segmental Height and Angular Correction in an Expandable Articulating Minimally Invasive Transforaminal Interbody Fusion

Presented at SMISS Annual Forum 2018
By L. Massie
With G Grady McBride MD,

Disclosures: L. Massie None G Grady McBride MD None,


Minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) with a lordotic, expandable, articulating cage has been proven to increase segmental height and segmental lordosis, both of which have been shown to be associated with improved pain and disability scores. Despite this interbody cage's advantages, cage placement can be technically challenging, with the surgeon having to balance operative time with more optimal cage placement.


We sought to quantify the effect of the final MIS TLIF cage position on improvement in segmental height and lordosis.


We examined a series of 75 patients who underwent MIS TLIF with a single surgeon at a total of 98 levels. Fifty-nine (78.6%) patients underwent single-level surgery, while 16 (21.3%) were treated at multiple levels. A lordotic, expandable, articulating cage was used in all cases. Segmental height and angle were assessed on pre- and post-operative standing radiographs. Interbody position (the angle of the long axis of the interbody cage in relation to the spinous process, and percent of interbody cage in the anterior half of the vertebral body) was assessed by a separate examiner using post-operative lumbar CT scan. Statistical analysis to assess the relationship of segmental height correction to interbody position was performed using multivariable logistic regression.


Significant increases in segmental height (pre = 4.34 mm, post = 7.77 mm, p<0.001) and segmental angle (pre = 4.73 deg, post = 9.74 deg, p<0.001) were again confirmed with the use of this expandable lordotic cage in this larger patient series. Using multivariable logistic regression, no significant differences in the increase in segmental height or segmental angle were found to be related to the angle of the interbody cage (coef= -.007 (95% -.03 - .01), p=0.595).


At this time, it does not appear that the degree to which the interbody cage is positioned transversely significantly impacts the amount of segmental height or segmental lordotic restoration in the use of this expandable, articulating, lordotic MIS TLIF cage. Further analyses are needed to assess the impact of cage position on patients' clinical outcomes and on coronal balance.