Anterior Lumbar Interbody Fusion May Provide Superior Decompression of the Foraminal Space Compared with Direct Foraminotomy: Biomechanical Cadaveric Study

Objective The objective of this cadaveric biomechanical study was to compare the area of the foraminal space during motion in the intact condition, after direct decompression via foraminotomy, and after indirect decompression via anterior lumbar interbody spacer insertion. Methods Eight (8) L5-S1 cadaver specimens were used for testing. Each specimen was tested in the intact state, after posterior foraminotomy, and after standalone anterior lumbar interbody fusion (ALIF). Each specimen was 3-dimensional imaged under neutral loading, flexion, and extension. The 3-dimensional images were analyzed for changes in the foraminal area under each loading scenario. A repeat-measures design was used. Outcome measures from testing included the frequency in which an increase in cross-sectional area was observed, as well as the percent increase of the foraminal area for each surgical group and loading direction. Results Direct foraminotomy and ALIF maintained the foraminal space during initial distraction under no loading with areas 99.7% and 96.5% of the native foraminal area, respectively (P = 0.955 and P = 0.455). Direct foraminotomy increased the foraminal area significantly during flexion to 112.2% of the area before motion (P = 0.008) while ALIF did not. Direct foraminotomy significantly decreased the foraminal area during extension to 89.2% of the area before motion (P = 0.006). ALIF, however, maintained its initial distraction during extension with 98.2% of the area before motion (P = 0.808). Conclusions ALIF maintains the foraminal area in extension while direct posterior foraminotomy does not.