Spinal Surgery- Principles

Question 1

Why do the effects of aspirin take 10 days to reverse?

Answer 1

Aspirin irreversibly blocks COX enzymes.

Plts have no nucleus and can thus not replace the enzymes.

The average life of a plt is 10/7, hence it takes 10/7 for the entire plt population to be replaced.

Question 2

How quickly can normal haemostasis be demonstrated in the context of antiplatelets?

Answer 2

Normal haemostasis can be demonstrated with as few as 20% normal plts and some studies now suggest the effects of aspirin can wear off after 2-4/7.

Question 3

Prone positioning for posterior cervical approaches?

Answer 3

Prone

Mayfield

Chin flexed and head lifted to maximise the space between the back of the shoulders and the occiput.

It is important to ensure the chin is not touching the operating table which will often be in a head-up position.

The arms are usually beside the patient.

Question 4

Prone positioning for lumbar spinal surgery?

Answer 4

Maybe on a frame or a spinal operating table that flexes the patient’s lumbar spine.

Important to get the width of the supports correct to prevent abdominal pressure (which impairs venous return).

Some surgeons use the knee-elbow position though care must be taken to avoid nerve palsies.

Question 5

Key considerations w.r.t. prone positioning?

Answer 5

Neck not overextended

Axillae not compressed.

No pressure on the eyes

No compression of external male genitalia.

Question 6

Positioning for anterior cervical spine surgery?

Answer 6

Horseshoe

Rolled towel behind the shoulders to aid neck extension.

Pad the eyes.

Question 7

Lateral positioning

Answer 7

Used for extreme lateral interbody fusion procedures

True lateral and AP views must be obtained to avoid parallax errors.

The surgical plane is perpendicular to sagittal which allows abdominal contents to fall forwards.

Neural monitoring, especially for the L4/5 level, is recommended to avoid injury to lumbar plexus

Question 8

Contraindications to extreme lateral interbody fusion approach

Answer 8

Anomalous vascular anatomy

Peritoneal scarring

Spondylolisthesis greater than grade II

Question 9

What approach to interbody fusion provides better access to L5/S1?

Answer 9

Anterior as the XLIF approach is limited by the iliac crests

Question 10

Complications of ALIF

Answer 10

Vascular injury

Visceral damage

Retrograde ejaculation

Sympathetic disruption

Question 11

Def: parallax error

Answer 11

The error/displacement caused in the apparent position of the object due to the viewing angle that is other than the angle that is perpendicular to the object.

Minimised by keeping needles close to the structure being marked and that the XR machine is correctly positioned.

Question 12

SSEPs

Answer 12

Sensory stimulus over a nerve measured with percutaneous electrodes over the sensory cortex

Question 13

MEPs

Answer 13

Measured from a muscle after a stimulus is given to the motor cortex

Question 14

SSEP threshold suggestive of dorsal column insult intra-operatively

Answer 14

10% increase in latency from baseline or a 50% reduction in amplitude.

Question 15

MEP threshold suggestive of anterior corticospinal tract injury

Answer 15

Any significant change in waveform considered significant SC insult as motor potentials are considered “all or nothing” by many neurophysiologists

Question 16

Fusion rates for ACDF

Answer 16

Around 90%

Question 17

What must happen for metalwork to succeed in spinal surgery

Answer 17

Bony fusion.

Question 18

Bony fusion in traumatic SC surgery vs MSCC

Answer 18

More likely to occur in trauma, therefore in MSCC the construct must be longer.

Question 19

Factors promoting bony fusion

Answer 19

Decortication of bone surfaces

Adding autograft (iliac crest)

Allogenic cancellous or decorticated bone

Question 20

Factors inhibiting bone fusion

Answer 20

NSAIDs odds ratio of 3.0 for non-union

Smoking also inhibits

Question 21

Recombinant bone morphogenic protein 2

Answer 21

Promotes osteoblast differentiation and is effective in promoting spinal fusion.

Safety concerns include include implant displacement, subsidence, infection, urogenital events, retrograde ejaculation, radiculitis, ectopic bone fromation, osteolysis and poorer global outcomes.

Question 22

Use of internal fixation in spinal surgery?

Answer 22

Correction of deformity:

Kyphosis, scoliosis

Stabilisation:

Fracture, dislocations, malignant and degenerative pathology

Question 23

General principle of screw-rod fixation systems

Answer 23

Utilise pedicles and lateral masses as fixation points

Allows instrumentation of the sacrum

Question 24

Parts of the screw

Answer 24

The section that contains the thread

Head

Variation of different types of screws is based on the type of head, the type of interface between the screw head and shaft, whether the shaft is fully or partially threaded and if the shaft is fenestrated.

Question 25

What are the two types of interface between the screw head and shaft?

Answer 25

Monoaxial Polyaxial

Question 26

Monoaxial screws

Answer 26

Do not allow movement between the screw head and the shaft

Question 27

Use of monoaxial screws

Answer 27

For deformity correction

Question 28

Polyaxial screws

Answer 28

Joint with a spherical head enclosed in a housing which allows the screw head to move in relation to the shaft Allow the surgeon some flexibility in connecting the screws to rods. Fail at the head-shaft interface rather than along the shaft or rod

Question 29

Subdivisions of polyaxial screws

Answer 29

Uniplanar- allow movement in the cranial or caudal plane only Multiplanar- allow movement in multiple planes

Question 30

Subdivisions of multiplanar polyaxial screws

Answer 30

Biased- allow angulation up to 55 degrees in one direction Non-biased- allow up to 30 degrees of angulation in each direction

Question 31

Types of shaft design

Answer 31

Fully threaded Smooth shank screws

Question 32

Features of smooth shank screws

Answer 32

10mm unthreaded segment and are used in the C1 lateral mass where the smooth shank is designed to prevent the thread irritating the C2 nerve root.

Question 33

Lag screws

Answer 33

Unthreaded segment and a distal half that is threaded Used in odontoid peg fixation where the thread sits in the peg and the shaft in the C2 vertebra Tightening the screw compresses the fracture thus improving bony fusion. Lag screw sits flush

Question 34

Features of fenestrated screws

Answer 34

A hole down the middle which enables K-wire insertion to guide screw placement or the insertion of cement down the screw

Question 35

Def: pitch of a screw

Answer 35

Distance travelled by the screw in one 360 degree turn Fine pitched screw travels a short distance, used in cortical bone and generally has a higher pull out strength Coarse screw travels further with each turn, requires less force to insert and is used in cancellous bone.

Question 36

Rescue screws

Answer 36

Can be used where a screw has a poor hold. Usually has a wider diameter and coarser pitch.

Question 37

Types of screw tips

Answer 37

Rounded- need tapping to start the screw off Self-tapping- has cutting flutes at the tip but still requires a pilot hole Self-drilling- sharp and not requiring pilot hole.

Question 38

Types of plates

Answer 38

Locking or non-locking/dynamic plates

Question 39

Locked plates

Answer 39

The screw is held in the plate so that the angle of the screw to the plate is fixed

Question 40

Dynamic plates

Answer 40

Allow some movement as the fracture settles

Question 41

Forces resisted by screw/plate or screw/rod vs cages

Answer 41

Scfew/plate- distraction Cage- compression

Question 42

Advantages of minimal access surgery

Answer 42

Less pain Less analgesia requirements Shorter duration of stay

Question 43

Disadvantages of minimally invasive spine

Answer 43

May be more difficult Risk of incorrect port placement More XR exposure Equipment is often extensive

Question 44

Prevention of infection in spinal surgery

Answer 44

Razer rather clippers for hair removal Laminar flow theatres (no RCTs) Gent scrub Double gloving Prophylactic antibiotics.

Question 45

VTE and spinal surgery

Answer 45

Early mobilsation, good hydration, compression stockings. LMWH

Question 46

Incidence of post-op compressive epidural haematoma

Answer 46

0-1%

Question 47

Component of the vertebral column

Answer 47

24 mobile vertebrae C7 T12 L5 Fused vertebrae S4-5 + C4

Question 48

What limits movement of mobile vertebrae?

Answer 48

Intervertebral discs Paired posterior synovial facet joints Intervertebral ligaments Paraspinal muscles

Question 49

Diurnal variation in length of vertebral column

Answer 49

2cn

Question 50

Age-related loss of vertebral column length

Answer 50

Related to dehydration fo the inrevertebral dsiscs

Question 51

Primary roles of the vertebral column

Answer 51

Protect the spinal cord Provide stability and mobility To control the transmittance of movement from the upper and lower extremities

Question 52

Curves of the spine

Answer 52

Cervical lordosis Thoracic kyphosis Lumbar lordosis Sacral kyphosis

Question 53

Which part of the vertebral column is responsible for the majority of the load transfer fo the spine

Answer 53

Anterior column (vertebral bodies and intervertebral discs)

Question 54

Typical articulation between two prevertebral vertebrae

Answer 54

Two posterior intervertebral facet joints between the inferior and superior articulating facets and the intervertebral disc. This creates three points of articulation between each vertebra

Question 55

The trend in width and depth of vertebra

Answer 55

They increase from cranial to caudal, corresponds with increased compressive strength due to the greater axial loads experienced in the more caudal segments.

Question 56

Microscopic arrangement of the vertebral body

Answer 56

Outer cortical layer Inner cancellous bone with the microarchitecture adapted so that the trabeculae are orientated along the lines of application of load to provide resistance to dynamic loading.

Question 57

How is the C1 vertebra atypical?

Answer 57

No vertebral body Anterior arch with odontoid peg directly behind it Flattened posterior arch with a small midline posterior tubercle The articular processes are medially orientated to permit both flexion/extension and rotational movements

Question 58

Answer 58

Question 59

Features of C2

Answer 59

Odontoid peg- a superior bony extension of the vertebral body Has the largest spinous process in the spine.

Question 60

Answer 60

Question 61

Subaxial vertebrae?

Answer 61

C3-7 Uniform morphology In this region, the uncinate processes on the superior anterolateral aspects of the vertebral bodies articulate with a corresponding articulation of the vertebral body above. This uncovertebral joints aids rotation in the cervical spine

Question 62

Features of thoracic vertebrae

Answer 62

Uniform morphology with a long inferiorly angulated spinous process and vertically orientated facet joints There are costovertebral joints from T1 to T12 that provide articulation between the vertebra and corresponding rib. There are also rib articulations on the transverse processes from T1 to T10. In this region, the ribs, sternum and intercostal structures provide extra stability.

Question 63

Orientation of lumbar facet joints

Answer 63

Sagittal plane

Question 64

Which cervical vertebra does not have a bifid spinous process?

Answer 64

C7

Question 65

Structure of intervertebral disc

Answer 65

Found between the inferior and superior endplates of the vertebrae above and below. Has a central nucleolus pulposus with a surrounding annulus fibrosis. Acts to transmit load, allow movement, provide stability

Question 66

Composition of the nucleus of the intervertebral disc

Answer 66

Comprised of mostly water (80-90%) Type 2 collagen and multiple hydrophilic proteoglycans. The interaction between the annulus fibrosis and these proteoglycans leads to a unique hydrostatic structure. When the disc is loaded in compression water seeps out and the height of the disc is reduced, but the turgidity of the nucleus allows the transmission of the force to the obliquely orientated fibres in the multiple lamellae of the annulus.

Question 67

Which fibres connect the annulus fibrosis to the cortical bone of the vertebral body?

Answer 67

Sharpey's fibres

Question 68

What happens to intervertebral discs with age?

Answer 68

The ability to resist axial compression. The proteoglycan composition of the nucleus changes with a decrease in water retention. There is a loss of disc height Disc bulbing is often seen. Asymmetric loading of the disc in a pathological curve of the spine leads to migration of the nucleus pulposus to the convex side causing disc bulging (not herniation).

Question 69

Posterior elements of the spinal cord

Answer 69

Laminae Spinous processes Bilateral facet joints

Question 70

Zygapophyseal joints=

Answer 70

Facet joints

Question 71

Features of spinal facet joints

Answer 71

Synovial plane joints between the superior and inferior articular processes of the lumbar vertebrae In the cervical cord, they are orientated coronally allowing flexion-extension, lateral bending and rotation. In the lumbar spine, they are orientated sagittally, resisting rotational movement but allowing flexion/extension.

Question 72

Why is there a lower incidence of anterior subluxation at L5/S1?

Answer 72

The facet joints have a more coronal orientation. Degenerative spondylolisthesis is thus more common at L4/5.

Question 73

Where is the spinal canal most narrow?

Answer 73

T7

Question 74

What structures can contribute to stenosis of the spinal canal?

Answer 74

Bulging of the annulus due to dehydration Overgrowth of facet joints due to OA Folding in of the ligamentum flavum due to disc height Causing the classical "Trefoil" appearance of the spinal canal.

Question 75

What connects the anterior and posterior elements of the vertebral canal?

Answer 75

Pedicles

Question 76

Features of the pedicles

Answer 76

Signficant variation in pedicle size and orientation seen through the spine. Smallest at T4

Question 77

Ligaments that provide stability to the spine

Answer 77

Anterior and posterior longitudinal ligaments Interspinous ligaments Ligamentum flavum Intertransverse ligaments Capsular ligaments

Question 78

Movement resisted by interspinous lkigaments

Answer 78

Flexion

Question 79

Movement resisted by anterior longitudinal ligament?

Answer 79

Strong attachment to the vertebral bodies but not the intervertebral discs. Rists extnesion

Question 80

Attachments of the ALL

Answer 80

Skull base to sacrum

Question 81

Posterior longitudinal ligament

Answer 81

Clivus to coccyx Provides limited resistance to flexion. Made up of two layers Attached to the intervertebral discs. Constrains herniation of the nucleus pulposus

Question 82

Extent of the ligamentum flavum?

Answer 82

C2 to S1 Close to the axis of rotation.

Question 83

Why is the ligamentum flavum yellow?

Answer 83

Due to its high elastin content

Question 84

What is the significance of the relatively high elastin content of the ligamentum flavum?

Answer 84

Prevents the ligament buckling in extension and narrowing the spinal canal diameter

Question 85

What is the tectorial ligament?

Answer 85

Cranial extension of the PLL

Question 86

Where is the ligamentum flavum deficient?

Answer 86

In the midline

Question 87

What are the capsular ligaments?

Answer 87

Capsule ligament enclosing the spinal facet joints,

Question 88

What are the components of the cruciate ligament?

Answer 88

It consists of the transverse ligament of the atlas, along with additional fibres above and below.These fibres are also known as "longitudinal bands

Question 89

What is the importance of the transverse ligament of atlas?

Answer 89

Significant role in prevent C1/2 subluxation

Question 90

Apical ligament of axis?

Answer 90

Runs from the tip of the odontoid peg to the skull base

Question 91

Alar ligament

Answer 91

Run from the sides of the odontoid peg to the skull base

Question 92

Ligamentous structures stabilising the cranio-cervical junction?

Answer 92

Cruciate ligament (transverse ligament and superior and inferior longitudinal bands) Apical ligament Alar ligaments Accessory part of tectrorial membrane Atlanto-occipital membrane

Question 93

Causes of congenital variation in spinal anatomy

Answer 93

Failure of segmentation or formation.

Question 94

Scoliosis results from what?

Answer 94

Three dimensional deformity.

Question 95

Klippel-Feil Syndrome Triad

Answer 95

Low posterior hairline Short "webbed" neck Limited cervical range of movement Associated renal/congenital cardiac disease/ brainstem abnormalities/ cerbical scoliosis/ Sprengel's deformity

Question 96

Sprengel's deformity

Answer 96

Sprengel's deformity (also known as high scapula or congenital high scapula) is a rare congenital skeletal abnormality where a person has one shoulder blade that sits higher on the back than the other.

Question 97

Pathophysiology of Klippel-Feil syndrome

Answer 97

Failure of formation or segementation of the cervical somites at 3-8/40.

Question 98

Categorisation of function othe spine

Answer 98

Static (protection of SC) Dynamic (provision of stability and mobility, to control transmittance of movement to the upper and lower extremities)

Question 99

Advice to patients with Klippel-Feil

Answer 99

Aim for conservative Mx unless spinal instability or neurological deterioration Avoid collision sports Frequently develop degenerative cervical conditions

Question 100

Normal flexion/extension at C0/C1

Answer 100

15 degrees

Question 101

Normal flexion/extension at C1/2

Answer 101

10 degrees

Question 102

Normal flexion extension in the subaxial C-spine

Answer 102

7 degrees in the upper 20 in the lower.

Question 103

Flexion-extension in lumbar spine

Answer 103

Increases caudally up to 20 degrees at L5/S1

Question 104

What prevents flexion in the thoracic spine?

Answer 104

Splinting by the ribs

Question 105

Rotation in the ccervical spine

Answer 105

45 degrees at C1/2 Between 7 and 10 degrees at each level. No rotation at Co

Question 106

At which level of the spine is there no lateral flexion

Answer 106

C1/2

Question 107

What is the functional spinal unit?

Answer 107

Two adjacent vertebrae with the intervening disc and associated ligaments. It is the smallest anatomical spinal segment that can be considered to exhibit the biomechanical characteristics of the whole spine.

Question 108

Hooke's law

Answer 108

For small displacements, the size of deformation is proportional to the force applied.

Question 109

What is the zone of plastic deformation

Answer 109

The point beyond the elastic limit at which a material totally recovers when a stress is applied.

Question 110

Coupled movements in the spine

Answer 110

Often coupled so that movements along one axis leads to a movement along another. This is mostly due to orientation of the facet joints e..g in the cervical spine where lateral bending results in rotation of the spinal processes away from the concavity of the curve.

Question 111

Def: Clinical stability of the spine

Answer 111

Described by White and Panjabi `the ability of the spine under physiological loads to limit patterns of displacement so as not to damage or irritate the spinal cord or nerve roots and in addition, to prevent incapacitating deformity or pain due to structural changes.