LAMINECTOMY, AND LAB (Grant's Dissector [16th Ed.] pp. 18-22) TODAY’S GOALS: 1. Review bony landmarks; pay particular attention to the osteology relevant to a laminectomy. 2. Review the of the (ligamentum flava, interspinous , supraspinous ligament). 3. Open the vertebral canal and dissect the meningeal coverings to expose the spinal cord.

The superficial back muscles have already been dissected in the previous lab, and will be revisited in the lab session on Shoulder and Scapular Region. Remember that the superficial group acts on the upper extremity. Review these 5 muscles: trapezius, latissimus dorsi, rhomboids, and levator scapulae. The deep muscle group constitutes the intrinsic muscles of the back. This group may be further subdivided into superficial, intermediate and deep intrinsic muscles. Review the splenius capitis and cervicis, and muscles of the erector spinae group (iliocostalis, longissimus, spinalis).

DISSECTION NOTES: Vertebral Canal and Spinal Cord Review the osteology of the spine relevant to a laminectomy (spinous processes, transverse processes, laminae). Remove the dorsal musculature from T6 to L5 levels by making scalpel cuts through the musculature adjacent to the spinous processes. Use the edge of a chisel to “scoop” away remaining muscle between the spinous processes and the transverse processes (i.e., from the transversospinal groove). Make a parallel cut along the tips of the transverse processes, then intersecting transverse cuts at the T6 and L5 levels. Lift out this strip of muscle. Observe the “groove” between the transverse and spinous processes that this musculature once occupied.

To expose the spinal cord, use a chisel (rather than a saw) to perform the laminectomy (Dissector p. 19, Fig. 1.14). Make a series of cuts (with the chisel edge directed medially at a 45° angle) through the lamina on each side. Watch out for flying bone chips…..really. Make connecting transverse cuts at the T6 and L2 levels. With care, you should be able to remove the dorsal portion of the vertebral arch between these levels as a single piece. Cut bone is sharp! Exercise caution when probing the site with your gloved hands. On the undersurface (vertebral canal side) of the “roof” of the bony segment removed, observe the ligamentum flavum connecting adjacent laminae. Between adjacent spinous processes, observe the interspinous ligaments. The supraspinous ligament is difficult to discern and extends between the tips of spinous processes.

Spinal Cord and Meningeal Coverings Observe the spinal cord with its meningeal coverings in situ. Recall the contents of the canal: extradural fat, internal vertebral plexus of veins (note clinical correlation on page 20 of Dissector), meningeal coverings and spinal cord. Now identify the following (page 21 Dissector - Figs. 1.16, 1.17):

• – make a longitudinal incision through this layer along the entire length of the exposed spinal cord. Just deep to it note the filmy “spider-webby” next layer, called the • arachnoid mater • subarachnoid space • • denticulate ligaments (extension of pia along the lateral margins of the spinal cord securing the spinal cord to the dura) • ventral & dorsal roots • dorsal root ganglion (DRG) (in an I.V. foramen) • conus medullaris (tapered end of the spinal cord that ends at the L1-L2 vertebral level) • cauda equina (“horse’s tail” collection of ventral and dorsal roots caudal to the conus medullaris) • (extension of pia; the intradural portion [filum terminale internum] extends to S2 vertebral level, and the extradural portion [filum terminale externum] attaches to the coccyx)

Note the clinical correlation on a lumbar puncture on page 20 of the Dissector.

PEER TEACHING GUIDE: Organize your narrative to minimally include: 1. A description and demonstration of the relevant osteology of the vertebral column and ligaments of the back. 2. A description and demonstration of the superficial and intermediate layers of deep back muscles. 3. A description of the laminectomy procedure to access the vertebral canal. 4. A description and demonstration of the contents of the vertebral canal, including the list of meningeal coverings and features of the spinal cord. 5. Additional props: Use a vertebral column to demonstrate relevant bony processes and ligaments.