1. Biomechanics of Nerve

2. Spinal Peripheral Nerves zNerve fibers z Connective tissue zVascular structures

3. Mechanical Properties z Resist - compression - tension

4. Characteristics z Small sensory fibers – pain etc. z Large motor fibers

5. Intraneural Connective Tissue Endoneurium z surround each fiber - collagen & fibroblasts Perineurium z provides mechanical strength & biomechanical barrier z Epineurium - outermost- protect fascicles, vascular supply

6. Intraneural Connective Tissue

7. Spinal Nerve Roots z devoid of: - epineurium - perineurium

8. Endoneurial Fluid z Interstitial fluid z Trauma   fluid pressure z  circulation  z  conduction

9. Injuries z Tension 2 0 trauma / child birth z Compression 2 0 to trauma / insidious

10. Mechanisms vs. Tension Injuries z dependent on perineurium for elasticity z dependent primarily on epineurium

11. Rabbit Tibial Nerve Elongation Load

12. Rabbit Tibial Nerve z Initially:low load  significant elongation z Elastic/linear region z disruption of endoneurial tubes & perineurium  rupture

13. Peripheral Nerves z Maximal elongation at elastic limit – 20% z Complete structural failure at 30% z Injury   stiffness   elasticity

14. Tensile Injuries to Brachial Plexus

15. zhigh speed MVA zfall from height zdirect hit to superior shoulder or lateral head (stinger) zchild birth

16. Nerve Regeneration zNerve rupture before endoneurial tubes & perineurium zpathway for regeneration z1 mm/day

17. Compression Injuries znumbness, pain, muscle weakness zischemia may be more important than actual compression zduration is important

18. Mechanisms of Compression Injuries zintermittent or constant low pressure  intraneural edema  fibrotic scar (common in spinal nerves) zproximal compression   axonal transport  distal nerve more susceptible to compression injuries (carpal tunnel)

19. Mechanisms of Compression Injuries zLarge nerves (motor) affected more zSmall nerves (sensory) spared

20. Factors influencing damage zDirect vs. indirect zMagnitude zDuration

21. Regeneration zIntact Schwann Cells zcompletely severed  no guiding structures preserved  no direction of regeneration  loss of sensory and motor function

22. Regeneration

23. Effects of Aging Diminished: zVibratory sensation z2 point discrimination zDTRs zNCVs (50-70 m/s in young,  10 m/s in 30-40) z Touch sensation

24. Effects of Aging z Slightly  pain threshold z  motor function z Functional recovery is less satisfactory