[Stability of lumbar spine after artificial disc replacement].

OBJECTIVE: To determine the influence of artificial disc replacement on the stability of lumbar. METHODS: Ten fresh human cadaveric lumbar spine specimens (9 males, 1 female) were tested. The donors had a mean age of 29.3 years old. The segments were fixed on a special testing device mounted in a universal testing machine. Physiological load with a maximum of 10 Nm was applied in the flexion, extension, right and left side bending. Moments were applied in 6 load steps: 0, 2, 4, 6, 8, and 10 Nm. Linearity migration and angle migration were recorded,and the mean flexibility coefficients were calculated. Four procedures of measurement were performed in every specimen: intact segments, segments after discectomy, segments after the artificial disc replacement, and segments after the artificial disc replacement with cutting posterior longitudinal ligament locally. RESULTS: The indexes we calculated of the segments after the discectomy were statistically different compared with the intact segments (P<0.05, P<0.01). The linearity migration,angle migration and mean flexibility coefficient in flexion/extension direction of the segments after the artificial disc replacement were statistically different compared with the segments after the discectomy (P<0.05, P<0.01), and there was a statistically significant increase in angle migration and mean flexibility coefficient in the extension direction compared with the intact situation (P<0.05). There was no statistically significant difference in 4 directions between the segments after the artificial disc replacement and the segments after the artificial disc replacement with cutting posterior longitudinal ligament locally (P>0.05). CONCLUSION: Artificial intervertebral disc replacement could keep the stability of the lumbar functional spine unit. There was no harmful effect of cutting posterior longitudinal ligament locally on the stability of lumbar while performing artificial intervertebral disc replacement when it is necessary.