THE EFFECTS OF ANTERIOR DISCECTOMY AND INTERPOSITION AL IMPLANT UPON LUMBAR MOTION SEGMENT STABILITY

The cadaver spine motion segment behavior under torsional load was evaluated with the disc intact, with partial anterior discectomy and with spacer insertion. The results of this study explain how anterior lumbar discectomy and interbody fusion (ALIF) affects the torsional stability of the motion segment. The pseudarthrosis rate of the anterior lumbar discectomy and interbody fusion (ALIF) is known to vary with leveL Therefore fifteen fresh human cadaveric degenerated discs at L3-4, L4-5, and L5-S1 levels were loaded in torsion: intact after anterior discectomy and, after spacer interposition and removaL Torsional rigidity of intactL5-S 1 was greater than L3-4 (41 %) orL4-5 (53%). Anterior discectomy significantly decreased the torsional rigidity compared to intact: L3-4 (73%) L4-5 (48%) and L5-S1 (55%). Interpositioning of spacer partially restored the torsional stability compared to discectomy: L3-4 (22%) L4- 5 (18%) and L5-S1 (38%). In conclusion, L5-S 1 degenerated discs are rotationally more stable than L3- 4 or L4-5. Anterior discectomy significantly increases torsional flexibility. Spacer interposition partially restores the disc's torsional stability which is most prominent at the L5-S 1 leveL Increased rotational flexibility seems related to pseudarthrosis rate.