Thorax Lab 3B

Lab 3B: Back and Laminectomy

Lab Objectives

dissection of the right side of the back (the other group did the left side)
removal of the epaxial muscles (erector spinae) to expose the posterior aspect of the vertebrae from C1 to T1
laminectomy to cut through all of the laminae from C1 to T1 to expose the spinal cord

A key learning goal for the back is to understand the distinction between the deep (intrinsic, epaxial) back muscles that are innervated by the dorsal=posterior ramus and the superficial back muscles that are innervated by the ventral=anterior ramus.

Exposing and studying the spinal cord will help solidify your understanding of roots, rami and spinal nerves.

Short List of Structures - 3B

Dissection of the Right Side of the Back

Follow the instructions in Lab 3A to dissect the right side of the back

Laminectomy

Before you Begin

The goal of the laminectomy is to cut the left and right laminae (singular lamina) and remove the spinous process to reveal the spinal cord, meninges, and associated structures. Laminectomy is also a surgical procedure (see clinical correlation at the bottom of the page).

You must be familiar with the anatomy of the spinal cord and vertebrae to preform this procedure so please look at the skeletons around the lab and call anatomy staff over if you have any questions.

Before making any cuts into the vertebrae

Clear away as much of the fascia, epaxial musculature, and ligaments as you can surrounding the vertebral processes and laminae from C1 to T1 using a scalpel. This will be a destructive process. You will need to remove chunks of the erector spinae epaxial muscles from the spaces lateral to the spinous processes. Clear more laterally than you think you need to, such that you have room to maneuver the chisel at an angle to the laminae. This will ultimately look like two 1-inch wide channels on either side of the spinous processes of the vertebrae.

Once you have removed enough tissue you should be able to visualize and/or palpate the lamina when you are ready to chisel. Refer to a skeleton in the lab to visualize the space you need to clear to make your cuts.

Use a chisel to break through the laminae of all the cervical vertebrae on both sides of the column. Your target should be to break through the laminae just medial to the transverse processes, as shown in the figure to the right and above. This wont take much force, if the chisel plunges in, you have gone too far and have probably severed the spinal cord.

After chiseling through all of the cervical laminae on both sides, pry them up as a unit. Do your best to leave the underlying dura mater as intact as possible. Use rongeurs to clean up the edges of the laminae and extend the dissection field as far as possible. Be careful of sharp edges of cut bone.

Observing the Spinal Canal Contents

Identify the following :

Epidural space – contains epidural fat and the vertebral venous plexus
Dura mater – a sleeve of dense connective tissue inside the vertebral canal

Use a scalpel or scissors to cut through the dura mater along its exposed length; carefully reflect the dura mater laterally, trying to retain the deeper arachnoid mater.

Subdural space – region between the dura mater (externally) and the arachnoid mater (internally); use a probe to separate the dura mater from the arachnoid mater
Arachnoid mater – located immediately deep and loosely attached to the dura mater, very thin

Cut through a region of the arachnoid mater.

Subarachnoid space – space deep to the arachnoid mater (externally) and the pia mater (internally); cerebrospinal fluid is contained within this space
Pia mater – intimately covers the spinal cord and cannot be grossly distinguished, with the exception of the denticulate ligaments and filum terminale
Denticulate ligaments – small bilateral projections of the pia mater that are attached laterally to the surrounding dura mater; seen above the level of L1
Anterior and posterior roots – observe that the denticulate ligaments separate them
Dorsal root ganglia – a swelling along each posterior root, in or lateral to the intervertebral foramina

Clinical Correlation: Laminectomy

Laminectomy is a surgical procedure that creates space by removing the lamina and neural spine that cover the spinal canal. Also known as decompression surgery, laminectomy enlarges the spinal canal to relieve pressure on the spinal cord or nerves. This pressure is most commonly caused by bony overgrowths within the spinal canal, which can be caused by arthritis. These overgrowths are sometimes referred to as bone spurs, and are a normal side effect of the aging process in some people.

Laminectomy is generally used only when more-conservative treatments — such as medication, physical therapy or injections — have failed to relieve symptoms. Laminectomy may also be recommended if symptoms are severe or worsening dramatically.

Text and images modified from MayoClinic.org

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