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BIOMECHANICS OF FUSION. Spinal Disorders. Trauma Fractures, Whiplash injury, etc. Tumor Infection & Inflammatory Disease Deformity Cervical & Low-back Pain Degenerative disease, such as disc herniation, stenosis, spondylolisthesis, etc. Goals of Spine Surgery. - PowerPoint PPT Presentation



  • Spinal DisordersTraumaFractures, Whiplash injury, etc.TumorInfection & Inflammatory DiseaseDeformityCervical & Low-back PainDegenerative disease, such as disc herniation, stenosis, spondylolisthesis, etc.

  • Goals of Spine SurgeryRelieve pain by eliminating the source of problemsStabilize the spinal segments after decompressionRestore the structural integrity of the spine (almost normal mechanical function of the spine)Maintain the correction Prevent the progression of deformity of the spine

  • Spinal FusionElimination of movement across an intervertebral segment by bone unionOne of the most commonly performed, yet incompletely understood procedures in spine surgeryNon-union rate: 5 to 35 %

  • Types of Fusion

  • Factors for Considerationin Spine FusionBiologic FactorsLocal Factors:Soft tissue bed, Graft recipient site preparation, Radiation, Tumor and bone disease, Growth factors, Electrical or ultrasonic stimulationSystematic Factors:Osteoporosis, Hormones, Nutrition, Drugs, SmokingGraft FactorsMaterial, Mechanical strength, Size, LocationBiomechanical FactorsStability, Loading

  • Properties of Graft MaterialsGraft MaterialsOsteogenic PotentialOsteoinductionOsteoconduction

    Autogenous boneooo

    Bone marrow cellso?x

    Allograft Bonex?o

    Xenograft bonexxo




    DBM = Demineralized bone matrix; BMP = Bone morphogenetic proteins

  • Bone Morphogenetic ProteinCarriers:Collagen, DBM, HA or HA/TCP CeramicsAnimal studies:Dog: 100% bilateral fusion (Sandhu et al.)Rabbit & Baboon: 100% bilateral fusion (Boden et al.)Goat: No enhancement in cervical interbody fusion (Toth et al.) Perspectives:Use of osteoinductive proteins may result in a more rapid, more reliable and more biomechanically sound fusion than the autograft gold standard.Issues need to be addressed: Dosage, Carrier, Mechanical environment, Technology for easier application methodProspective, blinded, and randomized clinical trials required

  • Mechanical Strength of GraftImportant particularly in interbody fusion50% of body weight on the lumbar spineAxial compressive load ranging from 400N during quiet standing to as high as 7000N during lifting

    Graft Materials:Autograft obtained from illiac crestHA/TCP Ceramics with various porosities

  • Compressive Strength (MPa) of the Illiac Bone Graft and HA/TCP Ceramics with varying Porosity

  • Graft Size EffectHeight:Enlarge the foraminal area (FA) as well as the IVD heightIn C-spine fusion: 2mm+baseline disc height of 3.5 to 6.0 mmThicker graft for smaller IVDH & Thinner graft for IVDH > 7 mmIn lumbar fusion: BAK threaded cage (13, 15, 17 mm) increased the FH significantly with minimal changes in lordosis (upto 29% in L4-5 & 33.8% in L5-S1). Cross-sectional Area:Too small x-area may increase the incidence of subsidence> 30% of the x-area of the vertebral body to carry minimum thoracic physiologic loads without trabecular subsidence.

  • Graft LocationThree Types of Fusion:Interbody fusion, Bilateral fusion, Posterior fusionInvestigated Parameters:Axial stiffnessAxial compression load, Bending moment, and Motion at the adjacent levels while apply 20 deg FLX and EXT at L3Load on the facetsBilateral fusion presented least amount of alteration in the mechanical properties of the adjacent, unfused segment, while providing good stabilization on the fused segment

  • Complications of Spinal FusionSpinal Stenosis:11 to 41% (Brodsky, 1970; Macnab, 1971)Complications at the Donor SitePain, morbidity, sepsis, reduced structural integrity, etc.>20% (Younger and Chapman, 1989)Junctional DegenerationDegenerated or prolapsed discStenosisOsteoarthritis of facetsSegmental instability

  • Future StudiesHealing Type:What type of healing occurs during fusion consolidation? Membranous bone formation, endochondral ossification, or both?Ideal Mechanical Environment:What is the ideal rigidity required?Molecular Biology of the Spine FusionWhat triggers bone induction?What is the sequence of gene expression occurring?Synthetic Graft Materials:DBM, HA/TCP Ceramics with Growth Factor