Peripheral Nerve Injuries 🧠⚡ Peripheral Nerve Structure Endoneurium… — هبد تخصص DPT - NU — TG.ME

Peripheral Nerve Injuries 🧠⚡ Peripheral Nerve Structure Endoneurium • Surrounds individual axons. Perineurium • Holds axons together in fascicles. Epineurium • Surrounds the whole nerve. ⸻ Seddon Classification 1. Neurapraxia (Demyelination / Conduction block) • Mildest nerve injury. • Caused by transient compression or stretch. • Only myelin is affected. • Axons remain in continuity. • No Wallerian degeneration. • Complete recovery if cause is removed. • Usually managed without operation. Examples: • Radial nerve compression → Wrist drop. • Mild CTS. ⸻ 2. Axonotmesis (Demyelination + Axon loss) • More severe blunt injury. • Axons and myelin are disrupted. • Connective tissue layers remain intact. • Complete loss of motor, sensory and autonomic function. • Wallerian degeneration occurs distal to the lesion. • Recovery occurs by axonal regeneration. • Recovery progresses from proximal to distal. Common causes: • Crash injuries. • Displaced bone fractures. ⸻ 3. Neurotmesis (Demyelination + Axon loss + All CT layers loss) • Complete nerve injury. • Axons and all connective tissue layers are disrupted. • Wallerian degeneration occurs distal to the lesion. • Recovery cannot occur spontaneously. • Requires surgical repair. • Recovery is never perfect. ⸻ Quick Comparison Feature Neurapraxia Axonotmesis Neurotmesis Myelin damage ✓ ✓ ✓ Axon damage ✗ ✓ ✓ CT layers damage ✗ ✗ ✓ Wallerian degeneration ✗ ✓ ✓ Surgery needed ✗ Usually ✗ ✓ Prognosis Excellent Good Poor ⸻ Sunderland Classification • Described five degrees of nerve injury. • Based on increasing anatomical disruption. • More detailed than Seddon classification. • Useful because recovery varies according to damage of endoneurium and perineurium. ⸻ Strength-Duration Curve (SD Curve) Definition • Relationship between stimulus strength and stimulus duration required to produce minimal excitation. • Indicates the strength of impulses required to produce muscle contraction. • Used in traumatic peripheral nerve injuries and LMN lesions. ⸻ Purpose To determine whether the muscle is: • Innervated. • Denervated. • Partially denervated. ⸻ Advantages • Simple. • Reliable. • Cheap. • Indicates proportion of denervation. • Less time-consuming. ⸻ Disadvantages • Cannot show full picture in large muscles. • Cannot identify lesion site. • Qualitative rather than quantitative. ⸻ SD Curve Patterns Normal Innervation • Lower curve. • Flatter curve. • Shifted to the left. ⸻ Complete Denervation • Curve rises steeply. • Shifted to the right. • No response to very short duration impulses. ⸻ Partial Denervation • Kink in the curve. • Shape indicates proportion of denervation. • Progressive denervation: • Kink appearance. • Increased slope. • Shift to the right. ⸻ Rheobase • Lowest intensity with maximum pulse duration that just stimulates muscle or nerve. ⸻ Chronaxie • Minimum time for which a current of intensity twice rheobase causes contraction. • Increased in denervated muscle. • Shorter chronaxie = greater excitability. Order of Excitability Nerve > Skeletal muscle > Cardiac muscle > Smooth muscle ⸻ Utilization Time • Time taken by a stimulus of rheobasic strength to excite the nerve and produce a minimal muscle contraction. ⸻ Minimal Time • Minimal duration sufficient to elicit minimal excitation. • Below this value → no muscle contraction. ⸻ High-Yield Exam Points ⭐ • Neurapraxia = Conduction block. • Axonotmesis = Wallerian degeneration + CT intact. • Neurotmesis = Complete nerve disruption + Surgery. • Normal SDC = Left & Flat. • Complete denervation = Right & Steep. • Partial denervation = Kink. • Chronaxie = Time at 2× Rheobase. • Shorter Chronaxie = Greater excitability. • Both Rheobase and Chronaxie increase in denervated muscle.