Biomechanical Effects of Facet Capsule Injuries in Posterior Lumbar Fusion Operations

ABSTRACT

OBJECTIVES: Although posterior lumbar fusion operations had been reported to accelerate spinal degeneration, there have been only a few studies for their biomechanical effects. We have studied the change of motion range at the vertebral joint one level above the fusion(UVJ) in pedicle screw fixation group(PSF)(n=13) where facet capsule was destroyed and in posterior lumbar interbody fusion group(PLIF)(n=8) where it was spared. PATIENTS AND METHODS:The patients were divided into early(3 to 6 months) and late(over 12 months) according to postoperative follow-up period. The flexion, extension and flexion-extension angles(FA, EA, FEA) were measured at the UVJ with pre-operative, early and late post-operative films. RESULTS: Mean age and male to female ratio were 52.7+/-9.3 and 13.2. Mean follow-up periods were 144.1+/-30.0 and 528.8+/-160.3 days in early and late groups, respectively. The FEA and FA in the late PSF(11.8+/-3.1, 8.5+/-2.9) were significantly greater than pre-operative angles(7.8+/-3.9, 5.1+/-3.7)(p<0.01, p<0.05). All angles in the PLIF showed no significant changes with time. The FEA and FA in the late PSF(11.8+/-3.1, 8.5+/-2.9) were significantly greater than those of the late PLIF(7.6+/-2.3, 3.4+/-2.0)(p<0.01, p<0.001). All angles at early follow-up period were similar between PSF and PLIF. The EA showed no significant change in relation with follow-up period or fusion method. CONCLUSION: As a result, the facet capsule injury in pedicle screw fixation seems to be related with increased flexion angle or degeneration of the adjacent joint above the fused vertebra in the late phase.