Thorax Lab 3b

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. Laminectomy is also a surgical procedure (see clinical correlation).

Before using the bone saw:

Clear away as much of the fascia, epaxial musculature, and ligaments as you can surrounding the vertebral processes and laminae from C7 to T12. 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 bone saw at an angle to the laminae (see Figures 4-2, 4-3). You should be able to visualize and/or palpate the lamina when you are ready to cut. Refer to a skeleton in the lab to visualize the space you need to clear to make your cuts.

The bone saw works best when it is only cutting through bone. You may also need the chisels and mallets to break through remaining bits of the laminae after using the bone saw.

Check that the bone-saw switch is in the “off” position before the saw is plugged in.

To perform the laminectomy:

Use care with the bone saw: keep your hands and fingers away from the blade. Refer to Figures 4-2 and 4-3 for demonstration of the angle of the saw blade. Cut into the lamina on the side furthest from you (Figure 4-2, e.g., standing on the right side of the cadaver, cut into the left lamina)

Turn on the saw and cut into the lamina of C7 vertebra, holding the bone saw so that the blade is at an angle (i.e., not cutting straight down, or horizontal – aim for a 45º angle). As the saw blade cuts through the lamina, you will feel the blade drop and resistance decrease when the bone is cut through all the way. Stop cutting when you feel the “drop” to avoid cutting the underlying dura mater. Continue this from C7 to T12. Repeat for the other side of the vertebral column.

Use a scalpel to cut and/or a chisel to loosen the spinous processes. You will now remove the cut portion of the vertebral column to visualize the spinal cord. Pry C7 away from C6 and T12 from L1 and pull away the cut portion of the vertebral column from the cadaver, freeing any remaining attachments with a mallet and chisel. Be careful around sharp edges of the remaining parts of the vertebrae.

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