Authors: Avani Vaishnav; Joshua Wright-Chisem, MD; Michael Steinhaus, MD; Sravisht Iyer, MD; Steven McAnany, MD; Todd Albert, MD; Catherine Gang, MPH; Sheeraz Qureshi, MD, MBA (New York, NY)

The type of cage used in MI-TLIF can impact several goals of the procedure, including optimizing disc and foraminal height, interbody fusion, and sagittal balance.

To assess if cage type has an impact on immediate radiographic outcomes in single-level MI-TLIF.

Segmental Lordosis(SL), Lumbar Lordosis(LL), Posterior Disc Height(PDH) were compared using lateral radiographs obtained pre- and post-operatively. Impact of demographic(age, sex, BMI), pre-operative radiographic(SL, LL, PDH) and operative factors(cage-type, cage-width, cage-position) on radiographic outcomes was assessed.

Of the 154 patients included, 55 received a Static Oblique, 63 a Static Articulating, and 36 an Expandable Articulating cage.

There was no significant difference in SL pre-(p=0.389) or post-operatively(p=0.613). A difference was seen in change in SL(p=0.023), with the expandable articulating cage showing the greatest increase, and an improvement from pre- to post-operatively(p=0.033).

A significant difference was seen in change in LL(p=0.050), with the static oblique and expandable articulating groups maintaining LL(p=0.238 and p=0.873), but the static articulating group showing decrease in LL(p<0.0001). 

There was a significant difference in PDH pre- and post-operatively(p<0.0001 and p=0.045). All three cages increased in PDH(p<0.0001), with the expandable articulating cage showing the greatest increase(p=0.009).

Regressions showed that pre-operative SL was the only significant predictor of post-operative SL(p<0.0001;R2=0.418) and change in SL(p<0.0001;R2=0.247); pre-operative LL of post-operative LL(p<0.0001 R2=0.609) and change in LL(p<0.0001;R2=0.227); and pre-operative PDH of post-operative PDH(p<0.0001;R2=0.360) and change in PDH(p<0.0001;R2=0.299).

Cage-type, cage-position and cage-width were not significant predictors of radiographic parameters.

Pre-operative radiographic parameters were predictors of post-operative parameters. While the static cages maintained SL, the expandable cage increased SL. The expandable cage had the lowest pre-operative PDH, likely reflective of the expandable technology allowing for cage-insertion even in collapsed disc spaces. The expandable articulating cage demonstrated benefit in increasing SL, maintaining LL and causing the greatest increase in PDH.