lowerextremitykey04 - SSN ANATOMY Workshop 4: Lower...

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SSN ANATOMY Workshop 4: Lower Extremity If you need a leg to stand on, we’ve got your back… 1. On your medicine rotation third year, a patient is admitted who is suspected of having bacterial meningitis, and you are asked to do a lumbar puncture. Before you do so, the resident pimps you on all of the structures the needle will pass through before it reaches the CSF. Without even blinking an eye, you answer…. . In order: skin, superficial fascia, SUPRAspinous ligament, INTERspinous ligament, ligamentum flavum, epidural space (containing the internal vertebral venous [Batson’s] plexus), dura mater then finally arachnoid CSF (NOTE: same structures for a spinal block/intrathecal anaesthesia, BUT only to the epidural space for epidural anaestesia) 2. Which levels of the cervical spine are responsible for…. Flexion/extension: atlantooccipital joint Rotation: atlantoaxial joint Lateral flexion (abduction): between C2-C7 Circumduction: combination of flexion/extension and abduction 3. Label the regions of the spinal cord (April 151-2). 4. IPSIlateral spinal cord crush injury—Brown-Sequard syndrome (April 153) Pathway affected Where does it cross? Clinical sequelae MOTOR —lateral corticospinal tract, which controls voluntary movement below the neck Lower brain stem Paralysis on IPSIlateral side SENSORY—dorsal columns (fasciculus cuneatus, gracilis), which carry touch, proprioception 2 nd order neuron decussates in the brain stem IPSIlateral anaestesia below the level of injury SENSORY—lateral spinothalamic tract , which conveys sharp pain and temperature 2 nd order neuron cell body resides in lamina of the dorsal horn and decussates through the ant. Commisure Loss of pain and temperature sense on CONTRAlateral side below level of injury Mnemonic for dorsal columns: “Your ass is grass”—the fasciculus GRACilis carries sensory (touch, proprioception) information from the LOWER extremities, and remember that the sensory neurons add on to the dorsal columns laterally as you go up the spinal cord; the f. gracilis are therefore medial, and the f. cuneatus are lateral.
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5. What is the highest corresponding vertebral level of the iliac crests, and why is this clinically relevant? (April 149, 155, 472) L4—landmark for spinal tap/epidural and spinal anaestesia—the low level on the vertebral canal ensures that the spinal cord has already terminated inferiorly; also the spinous processes of the lumbar vertebrae are more horizontal, improving access to the vertebral canal. Remember that the vertebral column outgrows the spinal cord after the fourth fetal month, resulting in the cauda equina (“law of descent”—spinal nerves still emerge from corresponding level of vertebral column). 6.
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lowerextremitykey04 - SSN ANATOMY Workshop 4: Lower...

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