Thoracolumbar vertebral column Flashcards
Describe the anatomic components of the vertebrae
What tendon attaches to the accessory process?
Tendon of the longissimus lumborum
What are the anticlinal vertebrae?
The thoracic vertebrae in which the dorsal spinous processes switch from a caudal to a cranial orientation (T11)
What are the 3 components of the intervertebral disc?
Nucleus pulposus, annulus fibrosis, cartilaginous end plate
What is the composition of the annulus?
Concentric lamellae of collagen
What is the composition of the nucleus pulposus?
Well hydrated, contains a mixture of glycosaminoglycans (chondroitin sulfate and keratin sulfate) and a dispersed matrix of type IV collagen
What are the three long ligaments and three short ligaments of the thoracic vertebral column?
Long ligaments: supraspinous, dorsal and ventral longitudinal.
Short ligaments: yellow ligament, interspinous, intertransverse
Additional ligament in thoracic vertebrae: intercapital (T2-T11)
Why is IVDH postulated to be less frequent cranial to T11?
Presence of the intercapital ligament ventral to the dorsal longitudinal ligament
Where do the spinal arteries originate?
Intercostal arteries
Where does the vertebral venous plexus drain?
Azygous
What are surgical approach options to the thoracolumbar vertebral column?
- Dorsal.
a. Cranial thoracic (T1-T5): trapezious and rhomboideus muscles are retracted, and the nuchal ligament at T1/T2 is preserved (continues as the supraspinous ligament).
b. Thoracolumbar (T6-L6): requires elevation of the multifidus muscle, and transection of the longissimus lumborum muscle on the accessory processes. - Lateral: indicated for lateral fenestration and lateral corpectomy from T10-L5 (see image). Requires blunt dissection through the epaxial musculature.
- Dorsolateral (separation between the multifidus and longissimus musculature). Useful for access to the lateral aspect of T9-L7.
Name the following instruments.
A, Adson periosteal elevator. B, Freer periosteal elevator. C, Surgairtome Micro100 pneumatic drill
What muscle has a thick tendinous attachment to the zygapophyseal joints?
Multifidus muscle (deep epaxial muscle)
What muscle has a thick tendinous attachment to the accessory processes of T11-L7?
Longissimus lumborum (superficial epaxial muscle)
What a structure approximates the ventral aspect of the vertebral canal?
Accessory process
What direction should the spinal nerve, artery and vein be retracted at each intervertebral disc space during fenestration?
Cranial
What are the three major portions of the vertebral column that provide stability?
Vertebral body: buttresses against axial loading and resists bending.
Articular processes: resist all forces.
Disc: Lateral bending and rotation
When should additional vertebral stabilization be considered following surgery?
Compromise of two or more of the stabilizing components of the vertebra (disc, body, joint), particularly bilaterally, traumatically or in a large breed dog
What are advantages/disadvantages of pediculectomy/mini-hemilaminectomy as compared to hemilaminectomy?
Advantages: preservation of the zygapophyseal joint, for pediculectomy (which is mini-hemilaminectomy but over one vertebral body) there is the additional advantage of avoiding the spinal nerve, artery and vein, it is faster, and associated with less hemorrhage.
Disadvantages: decreased exposure of the spinal cord, challenging orientation.
What are the different types of dorsal laminectomy procedure?
- Funkquist A
- Funkquist B
- Modified dorsal laminectomy (this is similar to the Funkquist A but the pedicles are undercut rather than removed and the cranial articular joints are left intact).
A thoracolumbar dorsolateral laminectomy with osteotomy of the spinous processes has also been reported and results in exposure of 75% of the spinal cord.
How accurate is radiography in determining the site of thoracolumbar IVDH?
57%.
What is vacuum phenomenon?
Gas radiolucency within the intervertebral disc space on radiography. Uncommon but highly specific finding for IVDH in one report.
What are the two locations for injection of contrast with myelography?
Cisterna magna or lumbar subarachnoid space
How accurate is myelography for the determination of lateralization of IVDH?
55-100% accurate.
What are the three basic myelographic patterns based on location of the pathology?
- Extradural.
- Intradural-extramedullary.
- Intramedullary.
What is the most common side effect observed with myelography?
Seizures - reported in 10-24% of dogs. Other reported complications include myelopathy, apnea, cardiac arrhythmias, meningitis, hemorrhage, death.
What increases the risk of seizures with myelography?
Cisterna magna injection and large breed dogs
What is central canal filling?
Filling of the central spinal cord with contrast following myelogram. Can result from inadvertent spinal cord penetration, contrast leakage, or communication between conus medullaris and subarachnoid space. Doesn’t impede diagnosis but may temporarily worsen clinical signs
What is the appearance of herniated disc material on CT?
Hyperattenuating compared to spinal cord, likely secondary to acute hemorrhage and mineral dense disc material.
What is the appearance of extruded disc material on MRI?
Normally hypointense on both T1 and T2W images. If hydrated (non-degenerative) can be hyperintense on T2 and isointense on T1 images. Can use STIR, FLAIR or T2* sequences to better delineate. Contrast enhancement is common on T1W post-contrast images.
How does signal hyperintensity on T2W images relate to prognosis of dogs with IVDH?
- T2W hyperintensity > 3-5 x the length of L2 associated with reduced return to ambulation.
- T2W hyperintensity >90% of the cross sectional area of the cord associated with poor long term function in ANNPE.
Why is myelogram contraindicated in patients with inflammatory CNS disease?
Can cause clinical deterioration.
What are the advantages/disadvantages of CSF collection from the cerebellomedullary cistern?
Advantages: easy to collect, free from blood contamination, easy to interpret.
Disadvantages: greater potential for morbidity. May not be altered with more caudal disease processes (due to rostral caudal flow of CSF).
Describe the characteristic CSF findings for a dog with thoracolumbar IVDH
Typically only mild pleocytosis. Increases in protein were higher at the subarachnoid lumbar location.
Dogs with higher protein concentrations, RBC count, and NCC had more severe injuries at the time of acquisition.
What are medical management options for the treatment of TL IVDH?
1) Enforced rest.
2) Use of analgesics, muscle relaxants, and corticosteroids.
3) Physical rehabilitation.
What are the documented success rates of medical management for thoracolumbar IVDH?
Ambulatory: 82-88%
Non-ambulatory: 43-51%
For non-ambulatory dogs surgery is associated with a higher likelihood and faster return to function.
Are corticosteroids currently recommended in the medical management of TL disc disease?
No - risk of complications (diarrhea, UTI), worsening quality of life scores, and no change in outcome in the literature.
What are surgical options for treatment of TL IVDH?
- Corpectomy.
- Hemilaminectomy +/- fenestration.
- Pediculectomy/mini-hemilaminectomy +/- fenestration.
- Percutaneous discectomy (may only be effective in patients with normal sensation pre-op).