ANATOMY - SPINE

Question 1

List the layers of soft tissues that the large bore needle will pass through when a lumbar puncture is performed. May use a well labelled diagram (8)

Answer 1

Skin, followed by the following layers [Pic right]

The Lumbar Puncture needle pierces in order: skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space containing the internal vertebral venous plexus, dura, arachnoid, and finally the subarachnoid space.

Question 2

In performing a Lumbar puncture, it is important to note the level of the point of termination of the spinal cord. This level varies according to whether your patient is a neonate, a child or an adult.

Describe the anatomy of the terminal portion of the spinal cord (5)

Answer 2

The spinal cord terminates at the level of L1 in an adult (embryonic sc develops slower than the vert col) the terminal part is called the conus medullaris. The filum terminalis (a fibrous strand composed mostly of pia) extends down from L1 to the coccyx. Nerve roots radiate inferiorly from the conus medullaris and are known as the cauda equina.
Internal terminal filum - pia part. External terminal filum - dura part (from where the dura terminates around S3.

Question 3

Explain (with the aid of diagrams) why the level of termination changes with age (5) (5+5 = 10)

Answer 3

Description of conus medullaris, filum terminale, terminations of spinal meninges (arachnoid and dura at S2), cauda equinae (5)
“Ascensus medullaris spinalis” – early growth and development of neural tube and spinal cord, later growth and development of vertebral column, leading to differential growth rates and apparent ascending of conus medullaris (S1 – L3/4 – L1/2) (5)

The embryonic spinal cord grows slower than the
embryonic vertebral column.

Question 4

Describe a commonly used test to determine intact function of lower segments of the spinal cord (1)

Answer 4

Knee-jerk (Patellar) reflex tests neural circuit involving mechanoreceptor (sensory neuron), interneurons and lower motor neurons in L2-L4 segment of the spinal cord that contracts the quadriceps muscle (also the Ankle reflex S1, S2; Plantar reflex reflex tests L4,L5,S1,S2 lateral aspects of the sole of the foot; Cremasteric reflex L1, L2 inner thigh).