Summary

The purpose of this study was to determine the impactof surgical decompressive procedures upon stiffness ofcadaveric canine lumbosacral motion units in the dor-soventralplane. Thirty-four grossly normal lumbosacralspecimens were potted, in aluminum channeling withpolymethylmethacrylate, and subjected to four-pointbending in dorsiflexion and ventroflexion, using a uni-versaltesting machine (Instron MA). In order to deter-mineits yield point, each specimen was non-destruc-tivelytested before and after surgical modification andthen tested to failure in ventroflexion. Dorsal laminec-tomy(L) did not have a significant effect upon stiff-nessof the lumbosacral motion unit in dorsiflexion orventroflexion, when compared with the control group.Since this also involved excision of the interspinousand supraspinous ligaments, removal of these struc-turesalone also did not have any significant effectupon dorsoventral stiffness in vitro. Compared withthe control group, the stiffness in the other groupschanged as follows: addition of discectomy (LD) didnot have a statistically significant effect in dorsiflex-ion,but decreased mean stiffness 33.1% (95% CI29.0 to 37.2) in ventroflexion. Dorsal laminectomycombined with bilateral facetectomy (LF) decreasedstiffness 43.5% (95% CI 39.4 to 47.6) in dorsiflex-ion,and 30.9% (95% CI 26.8 to 35.0) in ventroflex-ion.The combination of dorsal laminectomy, facetecto-myand discectomy (LFD) decreased the stiffness47.9% (95% CI 43.8 to 52.0) in dorsiflexion and56.4% (95% CI 52.3 to 60.5) in ventroflexion. Thisdecrease in stiffness in ventroflexion was significantlygreater than with laminectomy and facetectomy alone(25% less stiff; 95% CI 20.9 to 29.1).