The effects of foraminotomy and distraction-stabilization on the dimensions of the lumbosacral neuroforamen throughout range of motion

Degenerative lumbosacral stenosis (DLSS) in dogs can involve foraminal stenosis and L7 nerve root compression. Surgical options to expand the L7-S1 neuroforamen (NF) include foraminotomy and distraction-stabilization. However, the efficacy of these techniques when subjected to biomechanical loading is unclear. The study objective was to investigate the influence of spinal motion on the volume of the L7-S1 NF in the native spine and after foraminotomy and distraction-stabilization. Eight canine cadaveric spines were subsequently tested in 3 conditions: native, after unilateral foraminotomy and after distraction-stabilization of L7-S1. Spines were subjected to axial compression, flexion/extension, lateral bending and axial rotation. The volume of the L7-S1 NF was calculated for each condition and motion direction. Linear mixed models were used to analyze differences between motions and conditions. The NF in the native spine was only affected by flexion (+4.5 %±16.6;P < 0.01) and extension (-36.7 %±11.1;P < 0.01) when compared to the position neutral + axial compression. The NF dimension after foraminotomy increased in flexion (+20.4 %±24.6;P < 0.01) and decreased in extension (-35.9 %±9.3;P < 0.01). In contrast, the NF after distraction-stabilization was not affected by biomechanical motion. Foraminotomy resulted in significantly increased volumes in all loading conditions (+31.0-45.7 %;P < 0.01). Distraction-stabilization produced smaller, yet statistically significant, increases in foraminal volume across several loading directions: axial compression (+15 %±18.0;P = 0.01), ipsilateral lateral bending (+22.1 %±19.0;P < 0.01), extension (+75 %±31.6;P < 0.01) and ipsilateral (+9.3 %±12.9;P = 0.01) and contralateral axial rotation (+12.7 %±12.9;P = 0.01). Both foraminotomy and distraction-stabilization lead to significant increases in the volume of the L7-S1 NF throughout spinal movement. As such, either procedure may be effective in enlarging the L7-S1 neuroforamen compromised by DLSS.