Mechanics Research And Preliminary Clinical Observation Of A New Allograft Lumbar Cage

Background and objectiveCage is a critical device in the spinal interbody fusion. It can effectivelyintervertebral space distraction, so the ligaments surrounding muscles tense andmake upper and lower vertebral a relatively stable entirety. It provides axialsupport of the early fusion required and improve the fusion rate. Cage preventsloss of the intervertebral space and maintains the physiological spinal curvature.Currently commercially available fusion cage is made of metal, carbon fiber,polyether ether ketone (PEEK), and bio-absorbable materials. But there aresome drawbacks of these materials in terms of biology, biomechanics, etc.,mainly in terms of the elastic modulus is too large, poor biocompatibility, and socan not be absorb. Allogeneic bone is recognized bone graft material of greatosteogenic effect. It has the closest physicochemical properties, structure andactivity of protein-based composition of autologous bone, and rich in a varietyof cytokines required for osteogenesis. It has osteoconduction andosteoinduction characteristics and often used to repair human bone tissue.Allograft bone is the best natural materials to produce cage. There is noallograft cage for posterior lumbar fusion in the way of oblique singleimplantation. In response to these problems, the research team designed aanatomical allogeneic bone cage for posterior lumbar fusion. The cage use aunique splicing, can be implanted in a single oblique way. As a stress-sharingdevice, interbody fusion cage need to provide strong enough axial support. Butsplicing may influence mechanical properties of cage. The purpose of this studywas to explore the effects of different design and processing methods forbiomechanics of properties of the allograft cage and observe the preliminary clinical results.Materials and methods1.Use human femur bone to make allograft cage.2.We conducted materialproperty testing to compare the mechanical compressive strength of twodifferent mounting designs.3.Use the finite element method to analyze theeffect of geometry on their structural strength and stress distribution.4.Follow-up patients used the allograft cage from September2012to September2013in orthopedic department of Southwest Hospital. We use plain film and CTreconstruction to evaluated fusion rates, and measure and compare the changesin relative intervertebral space height. We use ODI score and VAS score toevaluate the clinical features of patient recovery.Result1. The material testing results indicate that the ultimate strength of anallograft cage with a dovetail slot mounting mechanism (11801.8±1822.0N) isgreater than that of an allograft cage with a right-angle slot mountingmechanism (5795.6±1311.9N).2. The results of finite element analysis howthat maximum stress concentration occurs around the side hole of the cage, witha side-hole diameter of2.0mm reflecting the best combination of high structuralstiffness(30.0MPa) with low stress concentration(333333.3N/mm).3.35patients(43segments) were followed. Follow-up rate is83.3%.Mean follow-up time is8.1months. The average age is52.2years old.16males and19females.4. Basedon the evaluation results of lumbar spine plain films, the fusion rate of3monthspost operation is90.2%, the fusion rate of6months post operation is92.7%.Thefusion rate is92.7%at final follow-up. Based on the evaluation results of CT,the fusion rate of3months post operation is92.7%, the fusion rate of6monthspost operation is95.1%.The fusion rate is95.1%at final follow-up.5. Thepreoperative average relative disc space height is0.71±0.21.The3dayspost-operative average relative disc space height is0.94±0.63. ThePostoperative relative disc space height is higher than the preoperative(p=0.000). The final follow-up relative disc space height (0.90±0.16)is higherthan the preoperative (p=0.000), and show no statistical significance compare to 3days postoperative.6. The mean preoperative ODI score is28.3±13.9, meanODI score is11.3±6.8at the final follow-up. The last follow-up ODI score issignificantly lower than the preoperative（p=0.000）.The mean preoperative VASscore is7.2±1.3, mean VAS score is2.6±1.0at the final follow-up. The lastfollow-up VAS score is significantly lower than the preoperative（p=0.000）.7.All patients have not the nerve root injury, wound deep infection, severeintervertebral sinking and other serious complications found. None of thepatients had interbody fusion cage move and fragmentation。Conclusion1. The new allogeneic bone cage is innovative and make up for gaps in themarket.2. The mechanical strength of the dovetail slot allograft cage is higherand a2mm side hole is able to maintain relatively low stiffness while avoidingoverstress concentration.3. The mechanical strength of the Splicing allograftcage is much higher than that of the endplate and completely meets the needs oflumbar interbody fusion.4. The new allograft posterior lumbar interbody fusioncage has advantages of fusion earlier, high fusion rate and low sink rate. It issafe and effective.5. Long-term clinical efficacy of the cage need for greatersample size and long follow-up confirmed.