biomechanics of nerve. spinal peripheral nerves znerve fibers z connective tissue zvascular...
Post on 20-Dec-2015
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Biomechanics of Nerve
Spinal Peripheral Nerves
Nerve fibers Connective tissueVascular structures
Mechanical Properties
Resist- compression- tension
Characteristics
Small sensory fibers – pain etc.
Large motor fibers
Intraneural Connective Tissue
Endoneuriumsurround each fiber - collagen & fibroblasts
Perineurium provides mechanical strength &
biomechanical barrier
Epineurium - outermost- protect fascicles, vascular supply
Intraneural Connective Tissue
Spinal Nerve Roots
devoid of:- epineurium - perineurium
Endoneurial Fluid
Interstitial fluidTrauma fluid pressure circulation conduction
Injuries
Tension 20 trauma / child birth
Compression 20 to trauma / insidious
Mechanisms vs. Tension Injuries
dependent on perineurium for elasticity
dependent primarily on epineurium
Rabbit Tibial Nerve
Elongation
Load
Rabbit Tibial Nerve
Initially: low load significant elongation
Elastic/linear region
disruption of endoneurial tubes & perineurium rupture
Peripheral Nerves
Maximal elongation at elastic limit – 20%
Complete structural failure at 30%
Injury stiffness elasticity
Tensile Injuries to Brachial Plexus
Tensile Injuries to Brachial Plexus
high speed MVAfall from heightdirect hit to superior shoulder or
lateral head (stinger)child birth
Nerve Regeneration
Nerve rupture before endoneurial tubes & perineurium
pathway for regeneration
1 mm/day
Compression Injuries
numbness, pain, muscle weakness
ischemia may be more important than actual compression
duration is important
Mechanisms of Compression Injuries
intermittent or constant low pressure intraneural edema fibrotic scar (common in spinal nerves)
proximal compression axonal transport distal nerve more susceptible to compression injuries (carpal tunnel)
Mechanisms of Compression Injuries
Large nerves (motor) affected more
Small nerves (sensory) spared
Factors influencing damage
Direct vs. indirect
Magnitude
Duration
Regeneration
Intact Schwann Cells
completely severed no guiding structures preserved no direction of regeneration loss of sensory and motor function
Regeneration
Effects of Aging
Diminished:Vibratory sensation2 point discriminationDTRsNCVs (50-70 m/s in young, 10 m/s
in 30-40)Touch sensation
Effects of Aging
Slightly pain threshold
motor function
Functional recovery is less satisfactory