1. Spine disorders are the most prevalent cause of chronic disability in persons less than 45 years old. 2. Second only to childbirth in accounting for hospital stays for patients under 65 years old. 3. In 1983, 250,000 spine surgeries in the U.S. 4. Annual prevalence of low-back disorders in US is 15% at any given time 5. In 1992,costs associated with low back estimate from $20 to $50 billion 6. Association between strenuous work/lifting and the severity of spine disorders 7. Example: workers performing heavy lifts from twisted position have 6 times the risk of acute lumbar disk problems compared to workers that perform lighter work 2

 How the musculoskeletal system work  For radiologist, orthopedist, neurologist and spinal neurosurgeon to diagnosis and treatment  And basic knowledge of physiology for internist  Needs to make prosthetic devices  Image guided CAD-CAM 3

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Basic knowledge: stress= force to the surface with interior effects= quality strain=measurable change in a shape of an object that stressed = quantity Σ = = elasticity 6 Stress Strain

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Biomechanics of spine fundamental and future Most fundamental equation is relationship: bending moment ”M”, force “F” and moment arm length ”D” M = F x D M has clinical significance in concentration of stresses All motions: flexion, extension, lateral bending and rotation are related together in combination and IAR=instantaneous axis rotation 12

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1. Distraction 2. 3 points bending 3. Tension-band fixation 4. Fixed moment arm cantilever beam fixation 5. Non-fixed moment arm cantilever beam fixation 6. Applied moment arm cantilever beam fixation 15

Maximum stress: leads to screw FX and fatiguing the implant Dynamic spine fixation “one decade ago” By offloading the implant from axial forces “passive telescopy of spine” for stability in rotation, flexion and extension and lateral bending 16

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New surgical strategies: 1. Utilization of intermediate fixation points “screws placed into intermediate vertebral bodies in multi- segmental constructs” to add a 3points bending fixation force application 2. Spine bio mechanics laboratory using implants in cadaver or biological specimen 49

50 T h a n k y o u F o r y o u r a t t e n t i o n