Ch 34 - Vertebral fractures, luxations and subluxations

Question 1

What percentage of dogs with vertebral fractures have concurrent injuries?
Thoracic?
Abdominal?
Pelvis or limb fractures?
Multiple vertebral fractures?

Answer 1

45-83% have concurrent injuries
- Thoracic 15 - 35%
- Abdominal 6 - 15%
- Pelvic or limb Fx 14 - 48%
- Multiple vert Fx 15 - 20% (more common in dogs under 15kg)

Question 2

What is the prognosis for dogs with intact nociception vs without?

Answer 2

Positive nociception - functional in upward of 80-90%
Negative nociception 12% waked again but none regained sensation

Question 3

What is the sensitivty and NPV of radiographs for identifying vertebral trauma?

Answer 3

• Sensitivity 72%
• Negative predictive value 48%

Question 4

What radiographic features are associated with poorer outcome in dogs

Answer 4

Degree of dislocation or axis deviation of the vertebral column

Question 5

What are the three compartments of the vertebral column?
How can these help with determining instability of fractures?

Answer 5

• Dorsal compartment - Spinous process, lamina, articular processes, pedicles, dorsal ligamentous complex (supraspinous, interspinous, joint capsule and ligamentum flavum
• Middle compartment - Dorsal annulus, dorsal longitudinal ligament, dorsal potion of vertebral body
• Ventral compartment - Remainder of vertebral body, remainder of annulus, nucleus pulposus, ventral longitudinal ligament

If moe than 2 of 3 compartments is compromised, considered unstable

Question 6

What forces do the following structures withstand?
- IVD
- Vertebral body
- Articular processes

Answer 6

• IVD - Rotation, lateral bending
• Vertebral body - All modes of bending and rotation
• Articular processes - rotation

Question 7

How does reperfusion cause secondary spinal cord injury?

Answer 7

Liberation of large numbers of oxygen free-radicals, causing destruction of neuronal and glial cell membranes via lipid peroxidation

Question 8

List the options for stabilisation of the TL column

Answer 8

• Pins and PMMA
• Locking plates
• ESF
• Vertebral body plates
• Modified segmental fixation
• Tension band stabilisation
• Spinous process plating

Question 9

How can increased abdominal pressure be detrimental when fixing spinal fractures?

Answer 9

Increased intraabdominal pressure (ie. from towels placed for positioning), can increase pressure within the low pressure, thin-walled internal vertebral venous plexus resulting in increased haemorrhage during surgery
This venous engorgement can also lead to decreased cord perfusion when combined with arterial hypotension

Question 10

What are the general guidelines for pin placement in the thoracolumbar vertebrae?

Answer 10

• Positive profile threaded pins
• 20-25% of vertebral body diameter
• Entry point at accessory process for thoacic, between base of transverse process and accessory process for lumbar
• Aimed to exit transcortex in region of end plates to maximise bone purchase
• Angled 30-60 degrees from sagittal plane

Question 11

What are the reported recommened pin insertion angles for the thoracic and lumbar vertebrae as reported by Wong et al, Wheeler et al, Watine et al?

Answer 11

Question 12

What important structures are at risk of being traumatised during pin placement through the vertebral bodies in the thoracic and lumbar column during fracture/luxation/subluxation stabilisation procedure?

Answer 12

• The azygous vein - lies just ventral to the right side of the thoracic vert column
• Aorta
• Pleura
• Lungs
• Caudal vena cava

Question 13

What steps can be taken during surgery to minimise the risks of improper pin placement?

Answer 13

• Always make a pilot hole
• Blunt-tipped pedicle probe to gently advance through cancellous bone
• Blunt right angel nerve hook to probe and ensure havnt broken through cortex
• Tip of trocar pin can be cut prior to transcortex
• Low speed, high torque drill

Question 14

What is the sensitivity of radiographs in detecting vertebral canal penetration with surgical implants?

Answer 14

May be as low as 50%
CT approaches 100%

Question 15

What are the general guidelines for locking plate application?

Answer 15

• Pin insertion at angles similar to those recommended for pin placement (30-60)
• Bilateral plating with minimum of three screws per vertebra
• Contoured to minimise lever arm while allowing offset to avoid interfering with neurovascular structures
• Penetration of transcortex is not essential

Can also place a unilateral plate on the lateral vertebral bodies - not as strong as 4pin-PMMA construct but stronger than intact spine ex-vivo. Bilateral plating is similar in strength to 4pin-PMMA constructs

Question 16

What plates can be used for spinal process plating?

Answer 16

• Bilateral metal Auburn spinal plates
• Bilateral plastic Lubra plates (38% implant removal due to pressure necrosis of spinal processes)

Nuts and bolts passed between (plastic plates) or through (metal plates) the spinal processes to connect them

Question 17

What is the preferred option if decompression is required?

Answer 17

Pediculectomy or mini-hemilaminectoym if possible

Question 18

What is the most common site for cervical Fx?
What is the perioperative mortality rate for cervical fracture fixation?

Answer 18

C1 and C2 account for 50 - 70% of cervical fractures
Perioperative mortailty rate 10 - 36%

Question 19

What is the cause of respiratory dysfunction in cervical spinal lesions?

Answer 19

• Phrenic nerve (C5-C7) and intercostal nerves are under the UMN control of the reticulospinal tracts

Question 20

What are the main two options for fixation of cervical vertebral Fx?

Answer 20

• Pins and PMMA
• Plating

Question 21

What retractor is especially associated with over reduction of cervical spinal Fx?

Answer 21

Scoville-Haverfield

Question 22

What anatomical features make implant placement in the cervical spina particularly complex?

Answer 22

• Narrow pedicles
• Transverse foramina (containing vertebral artery, vein, nerve)
• Very narrow safe corridor

Question 23

What is the average ideal insertion angle for C3-C6?
What is the average width of the safe corridor?

Answer 23

• Angle of insertion 34.2 - 37.5
• Safe corridor ranges from 1mm in a 4 kg dog, up to 4.5mm in 50kg dog

Question 24

What is unique about the C7 vertebra? How does this aid implant placement?

Answer 24

It lacks a transverse foramen
- Implant placement is more forgiving and average safe insertion angle 47.5 degree. In this way, it’s less likely to violate the vertebral foramen without risking to damage the transverse foramen (like in the other cervical vertebrae).

Question 25

What options are there for stabilising fractures of the cervical spine to avoid the risks of transverse foramen trauma

Answer 25

• Transverse process screws and PMMA
• Ventrally applied monocrotical screw and PMMA with three screws per vertebra (biomechanically comparible to bilateral 4pin-pMMA construct) 9.7% penetrated the vertebral canal

Question 26

What is unique about C2 which must be taken into consideration when planning fracture repair

Answer 26

• Thin central vertebral body providing little purchase for implants
• Construct stability should be increased by croseeing the AA joints with the implants (directed craniolateral, 30-35deg from sagittal plant, 40-45 degree in transverse plane, aiming for a point just medial to alar notch and transverse foramen of C1)
• Pins in caudal C2 can be directed laterally at 30-50 degrees

Question 27

What is an alternative for pins and PMMA for stabilisation of cervical Fx?

Answer 27

• Locking plates! (Human cervical spin locking plate (CSLP, Synthes), human maxillofacial locking plate (ComPack UniLock, Synthes), veterinary locking plates (SOP, Orthomed)(LCP, Synthes)
• A standard 3.5mm LCP applied ventrally using monocortical screws provides similar stability to 4pin-PMMA constructs. All pins had purchase of over 50% vertebral body

Question 28

What is the classical LS fracture orientation?

Answer 28

Cranioventral displacement of sacrum and small caudoventral wedge of L7 body

Question 29

WHat is unique about the L7 vertebrae?

Answer 29

The pedicles are considerable thicker and can accomodate pins or screws

Question 30

What are the landmarks for LS screw placement?

Answer 30

L7 pedicle screws
- Enter just caudal to the base of the cranial articular process
- Directed ventrally, as well as slightly cranially and medially

Sacral
- Enter just caudal to cranial articular process
- Placed ventrally, slightly ventrolaterally or slightly ventromedially
- Caudal pins may engage ilium by directing caudoventrolaterally through sacrum and across SI joint and into long axis of the body of the ilium

Question 31

What effect may NSAID have on the CNS?

Answer 31

• May act directly on spinal cord and higher centers to modulate nociception via inhibition of prostaglandin synthesis

Question 32

What is the overall prognosis for spinal fractures?

Answer 32

• No nociception likely around 5%
• Cervical fractures overall 70% with 13x greater chance of recovery in ambulatory patients
• TL fractures good prognosis with intact nocicpetion 80-100% with surgery, 85-95% with conservative management
• LS Fx v. good prognosis. Likely worse prognosis if absent tail tone, external anal sphincter tone, and absent perineal sensation

Question 33

What is an alternative for pins and PMMA for stabilisation of cervical Fx?

Answer 33

• Locking plates! (Human cervical spin locking plate (CSLP, Synthes), human maxillofacial locking plate (ComPack UniLock, Synthes), veterinary locking plates (SOP, Orthomed)(LCP, Synthes)
• A standard 3.5mm LCP applied ventrally using monocortical screws provides similar stability to 4pin-PMMA constructs. All pins had purchase of over 50% vertebral body