The Impact of the Cage Height, Diameter and Positioning on Clinical and Radiographic Outcome of the Extreme Lateral Interbody Fusion

Presented at SMISS Annual Forum 2013
By Christoph Hofstetter MD, PhD
With Roger Härtl MD, Marjan Alimi MD, Eric Elowitz MD,

Disclosures: Christoph Hofstetter MD, PhD Roger Härtl MD B; Brainlab, DePuy-Synthes, Ulrich, Marjan Alimi MD None., Eric Elowitz MD B; NuVasive,

Introduction: Extreme lateral interbody fusion (ELIF) is a novel technique for anterior spinal fixation and indirect decompression of neural elements.

Methods: Retrospective analysis of 145 ELIFs in 90 patients. Cages measuring 8 - 14 mm in height were used. Intervertebral disc height, foraminal height, cage position and lumbar lordosis were determined on pre-operative, post-operative, and the latest follow-up studies. Clinical outcomes were evaluated by Oswestry Disability Index and Visual Analogue Scale.

Results: At the time of last follow-up (17.7 ± 1.1 months), two factors determined restoration of foraminal height: First, the amount of oversizing the graft (implant height - preoperative disc height) showed a significant positive correlation with increase of foraminal height (Person correlation coefficient 0.691, P < 0.001). Implantation of cages 6 - 9 mm higher than the preoperative disc resulted in 3.1 ± 0.3 mm foraminal height increase. Thus, cages oversized by 6 - 9 mm yielded in significantly greater restoration of foraminal height compared to grafts that were oversized by 0 - 3 mm (P < 0.01) or 3 - 6 mm (P < 0.05). The second determinant of foraminal height restoration was the footprint of the intervertebral spacer. Approximately one half of our patients received 18 mm spacers and the other 22 mm grafts. 18 mm spacers allowed for a 2.1 mm increase of foraminal height while 22 mm spacers lead to an increase by 4.0 mm on postoperative radiographs (P < 0.001). Interestingly, neither cage position nor posterior instrumentation had statistically significant influence on restoration of foraminal height. ELIF interbody grafts provided adequate anterior column support with 1.0 ± 0.1 mm subsidence on last follow-up imaging compared to immediate postoperative studies. Subsidence was significantly greater with intervertebral cages that were oversized by 0 - 3 mm (1.7 ± 0.5 mm) compared to cages oversized by 6 - 9 mm (0.8 ± 0.2 mm, P < 0.05). One third of patients received lordotic spacers. Both, lordotic and non-lordotic cages allowed for increased lumbar lordosis on post-operative imaging (6.0 degrees, 4.7 degrees, respectively). Clinical evaluation revealed a mean ODI, VAS back, buttock and leg pain improvements of 21.1 %, 3.7, 3.6 and 3.7 points, respectively. 

Conclusion: In ELIF, cage width and height but not cage position determine restoration of foraminal height. Thus, optimum foraminal height restoration is achieved by using 22 mm wide cages oversized by 6 - 9 mm in height.