Lumbar intradiscal pressure after posterolateral fusion and pedicle screw fixation

In vitro biomechanical testing was performed in single-functional spinal un its of fresh calf lumbar spines, using pressure needle transducers to inves tigate the effect of posterolateral fusion (PLF) and pedicle screw construc ts (PS) on intradiscal pressure (IDP), in order to elucidate the mechanical factors concerned with residual low back pain after PLF. IDP of 6 calf lum bar spines consisting of L4 and L5 vertebrae and an intervening disc was me asured under axial compression, flexion-extension and lateral bending in th e intact spine, PS, PLF and the destabilized spine. Relative to the intact spines, the destabilized spines showed increased IDP in all of lordings and moments. IDP under PS and PLP mere significantly decreased in axial compre ssion, extension and lateral bending loads (p<0.05). In flexion, IDP under PS and PLP increased linearly proportional to the magnitude of flexion mome nt and reached as high as IDP of the intact spines. These results demonstra ted that despite an increase in the stiffness of motion segments after PLP and PS, significant high disc pressure is still generated in flexion. Flexi bility of PS and PLF may cause increased axial load sharing of the disc in flexion and increased IDP. This high IDP may explain patients' persisting p ain following PS and PLF. (C) 1998 Tohoku University Medical Press.