Compare Of Instrumented And Non-instrumented Anterior Lumbar Spinal Fusion For Adjacent Segment Degeneration: A Biomechanical Experimental Study In Rabbit

【Objective】(1)To establish animal models of anterior lumbar fusion(ALF) with and without instrumentation for biomechanics.(2) To use biomechanical test method, compare the different rate and adjacent segment degeneration(ASD)in two established animal models.(3) To compare the rate of fusion in instrumented and non-instrumented anterior lumbar fusion animal models.【Methods】A total of forty healthy adult New Zealand white rabbits were randomized to one control and two experimental groups:①sham operation: no lumbar fusion, no instrumentation,(n=8);②non-instrumented fusions: underwent anterior lumbar fusion surgery alone(n=16);③instrumented fusions: underwent anterior lumbar fusion with internal fixation(n=16).After 12 weeks of surgery, the L2-S1 spine were harvested. The spinal fusion was evaluated by radiography, manual palpation. The fusion spinal specimens were check by X-ray to evaluate the level of intervertebral disk degeneration in Andersen grade. The motion of the segment which adjacent to the level of fusion was evaluated by mechanical testing in four pure moment(flexion and extension, left and right lateral bending)to determine the range of motion(ROM) and neutral zone (NZ).【Results】Fusion status was evaluated by biomechanical testing, manual palpation and radiographic assessment at 12 weeks after surgery, the fusion rate of instrumented and non-instrumented fusion at 12 weeks was 42.9% (6/14) and 58.3 % (7/12) respectively. There was not significantly difference between the two groups (P>0.05). According to the Andersen grade, the ratio of adjacent superior and inferior disc degeneration in non-instrumented group was 83.3%(5/6) and 50%(3/6) respectively. And in the instrumented fusion group ,the ratio was 71.4%(5/7) and 57.1%(4/7), respectively. There was not statistically different between instrumented and non-instrumented fusion. Comparing to the control group, the range of motion(ROM) and the neutral zone (NZ) of the adjacent superior segment(L3-4) in experimental groups was statistically different(P<0.05). The different ROM and NZ of adjacent superior segment between non-instrumented and instrumented fusion spine was also significantly (P<0.05).There was not statistically difference for ROM and NZ among all three groups in adjacent inferior segment (P>0.05),the addition of internal fixation did rise the risk of ASD.【Conclusions】It is applicable to establish a new kind of animal models of anterior lumbar fusion with and without instrumentation; Radiographic assessment and manual palpation showed that the use of spinal instrumentation improved the fusion rate at 12 weeks (50% versus 75% in radiographs,42.9% versus66.7% in manual palpation,P>0.05). Comparing to the control group, the incidence of ASD is greater both in the surgery groups; The using of internal fixation rise the risk of ASD in anterior lumbar fusion.