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Posterior Spinal Fusion for Idiopathic Scoliosis

Preoperative Patient Care

A

Intermediate Evaluation and Management

1

Obtain focused history and performs focused exam

  • interpret neurological exam

2

Appropriately orders and interprets advanced imaging studies

  • MRI
  • CT scan

3

Prescribes and manages nonoperative treatment

  • medical management
  • make referrals to other professionals

4

Makes informed decision to proceed with operative treatment

  • documents failure of nonoperative management
  • describes accepted indications and contraindications for surgical intervention

5

Provides, modifies and adjusts procedure and patient specific post-operative management and rehabilitation

  • postop: 2 week postoperative visit
  • wound check
  • weaning off pain medication
  • postop: 6 week postoperative visit
  • wound check
  • diagnose and management of early complications
  • postop: ~ 3 month postoperative visit
  • repeat xrays of spine
  • evidence of fusion is difficult to see on radiographs
  • advance spine restrictions and activity levels
  • diagnosis and management of late complications
C

Preoperative H & P

1

Obtain history and perform basic physical exam

  • history: the following warrant further evaluation
  • back pain that is well localized, constant or worsening
  • weakness/clumsiness or gait abnormality
  • bowel/ bladder incontinence or ejaculating problems
  • physical exam
  • assess strength and sensation
  • check for foot deformity (unilateral= especially concerning)
  • lack of rotation on adams forward bending in scoliosis patients is abnormal
  • popliteal angles should be less than 50 degrees
  • kyphosis suggests curve may not be idiopathic

2

Order basic imaging studies

  • standing PA and lateral radiographic films of the entire spine
  • spine bending films to assess curve flexibility
  • MRI of cervical, thoracic and lumbar spine if indicated
  • atypical curve pattern, kyphosis, widened pedicles, lack of rotation through curve, winking owl sign, sharp curvature, rapid curve progression (>1 degree per month), pain that is localized/constant/worsening

3

Screen medical studies to identify contraindications for surgery

  • confirms no recent infection contraindicating surgery (UTI)

4

Perform operative consent

  • describe complications of surgery including
  • failure of fusion
  • implant misplacement, migration or failure
  • neurologic injury (paralysis including motor, sensation or bowel/bladder function)
  • superficial or deep wound infection
  • dural tear
  • pneumothorax
  • crankshaft or progression of the deformity above or below the fusion

Operative Techniques

E

Preoperative Plan

P

1

Identifies level of deformity on preoperative imaging

  • Identifies curve pattern (Lenke classification)
  • measures Cobb angle
  • counts number of vertebrae in the thoracic and lumbar spine
Pitfalls
  • Be sure to count vertebra as there are an abnormal number in 10% of AIS patients (Skaggs et al, JBJS 2013)

2

Template instrumentation on preoperative imaging studies

  • identifies intended levels of fusion
  • measures size of pedicles and length of vertebral body
  • do not end fusion level at apex of scoliosis or kyphosis
  • in general the lowest instrumented vertebrae (LIV) included in the fusion should be touching the center sacral line
  • when fusing to the lower lumbar spine in patients with significant leg length discrepancy plan on either leaving the LIV tilted in line with the leg length discrepancy or plan on fixing the leg length discrepancy

3

Execute surgical walkthrough

  • describe the steps of the procedure to the attending prior to the start of the case
  • describe potential complications and steps to avoid them
F

Room Preparation

1

Surgical instrumentation

  • complete set of instruments and implants
  • Lenke probe
  • ball tip probe
  • pedicle screws and hooks
  • rods
  • autologous and allograft bone for fusion

2

Room setup and equipment

  • table
  • radiolucent Jackson or other spine table
  • neuromonitoring
  • neuromonitoring leads to upper and lower extremities for SSEPs and MEPs
  • C-arm
  • c-arm perpendicular to table

3

Patient positioning

  • Prone with arms at 90° max abduction and elbow flexion to prevent axillary nerve injury
  • Foam padding on chest so that nipples are pointing midline straight down
  • Abdomen hanging free to prevent venous congestion
  • Chest, ASIS and knees well padded
  • Hips and knees slightly flexed
  • Foley in place
G

Posterior Approach- Superficial Dissection

P

1

Localize level of incision with C-arm

  • Identify pedicle of the upper instrumented vertebrae(UIV) and lower instrumented vertebrae (LIV) with C-arm and mark skin

2

Make midline incision.

  • Make Midline skin incision with 15 blade overlying the spinous processes
  • make the incision through the dermal layer only

3

Dissect subcutaneous tissue down to fascia

  • Deepen the incision to the level of the spinous processes using bovie electrocautery
  • Use weitlaner retractors to retract the skin margins
  • Identify the interspinous ligament between the spinous process
  • this has the appearance of a white line
  • as the incision is deepened, keep the weitlaner retractors tight to help with the exposure and to minimize the amount of bleeding
Pitfalls
  • Be careful not to violate the interspinous ligament above the UIV or below the LIV as this may lead to junctional issues

4

Open the cartilaginous caps over the spinous processes

  • Bisect longitudinal cartilaginous caps overlying the spinous processes at the midline
  • this is not done at the spinous process of UIV or LIV- preserve the interspinous ligament above the UIV and below the LIV by disecting just lateral to the spinous process at these levels
H

Posterior Approach- Deep Dissection

1

Perform subperiosteal dissection

  • Perform dissection with Cobb and Bovie electrocautery along spinous processes
  • care is again taken to preserve the interspinous ligament at UIV and LIV
  • Avoid inadvertent disruption of soft tissue and facet joint capsule surrounding facet joint below the LIV

2

Extend the dissection laterally

  • Continue the dissection laterally to the tips of the transverse processes

3

Maintain/obtain hemostasis

  • Move the weitlaner (+/- cerebellar) retractors to a deeper position for retraction and hemostasis as the levels are exposed.
  • Coagulate the branch of segmental vessels located just lateral to each facet

4

Confirm that all desired levels are exposed

  • Obtain an image with c-arm fluoroscopy to confirm UIV and LIV
I

Remove spinous processes and perform facetectomies

1

Remove spinous process with horsley bone cutter

  • DO NOT remove spinous process of UIV or LIV
  • Save bone from spinous process for later use as autograft

2

Perform facetectomies

  • Remove inferior 5-10 mm of inferior facet
  • in the lumbar spine this can be done with an osteotome (or bone scalpel). Alternatively, a rongeur or burr can be used to remove the facet in its entirety
  • in the thoracic spine this is done with an osteotome, bone scalpel or burr
  • Some surgeons use this bone for autograft, however, the authors do not do this as it contains a significant amount of cartilage which may impair fusion
J

Lumbar Pedicle Screw Placement

P
P

1

Identify the pedicle starting point(Lumbar)

  • Make sure that the full facet joint, transverse process and pars interarticularis are exposed
  • in the lumbar spine, the pedicle is located at the junction of the pars interarticularis and the midpoint of the transverse process
  • if anatomic landmarks are not clear or pedicle tract is not easily found, then c-arm fluoroscopy can be used to identify the pedicle starting point
  • Rotate c-arm clockwise or counterclockwise to obtain an image where the pedicle is the largest, thus the angle of the fluoroscopy shows the surgeon the angle of the pedicle
  • tilt the c-arm towards the head or feet to adjust for kyphosis/lordosis to obtain an image where the endplates and disc spaces are clear and identify pedicle
  • a high speed cortical burr is used to mark starting point and just penetrate cortical surface

2

Enter the pedicle(Lumbar)

  • Insert a gear shift pedicle probe into the pedicle with the tip pointing laterally at the identified starting point
  • there is often a cancellous soft spot at the entry point into the pedicle (in smaller pedicles this may not be appreciable)
  • an alternative method is to use a small drill bit 2.0mm at slow speed which allows one to feel cortical versus cancellous bone, then repeat with a 3.2 mm drill bit to widen tract.

3

Advance the gear shift pedicle probe(Lumbar)

  • advance the probe using slight ventral pressure and axial rotation to a depth of 20 mm
  • the transverse angle of insertion decreases as one moves cephalad from 30 degrees at L5 to 10 degrees at L1
  • the angle of insertion also needs to take into account the rotation of the vertebrae from the scoliotic deformity
  • after advancing to a depth of 20mm the gear shift pedicle probe is removed and the tract is probed with a sounding probe (ball tip probe)
  • medial, lateral, superior and inferior walls and the endpoint (floor) are palpated for any possible breech
  • if no breeches are appreciated, the gear shift pedicle probe is reintroduced pointing medially
  • the probe is advanced to the appropriate depth by rotating with slight ventral pressure
  • in adolescents this is typically around 40-45 mm but may vary significantly
Pearls
  • Avoid using significant ventral pressure so that penetration of the anterolateral cortex of the vertebrae is avoided

4

Probe the tract(Lumbar)

  • probe the tract using a flexible sounding probe (ball tip probe)
  • palpate the superior, inferior, medial and lateral walls and the endpoint (floor)

5

Measure the depth of the tract(Lumbar)

  • with the sounding probe tip on the endpoint of the tract, measure the depth by clipping a hemostat at the entry point
  • the sounding probe can then be held next to the screw to confirm the appropriate length
  • some surgeons follow this step by tapping the tract (the authors generally avoid this step)
  • if the pedicle tract was tapped, then probe the tract again for breech

6

Place the pedicle screw(Lumbar)

  • place the screw slowly in the orientation of the tract that was created

7

Identify the pedicle starting point(Thoracic)

  • confirm that entire superior facet joint is exposed
  • in the cephalad-caudad direction, the starting point is at the midpoint of the transverse process (TP) at T12, then moves up to the upper border of the TP at the mid thoracic spine (T7-T9) and back to the midpoint of the TP at the upper thoracic spine (T1-T2)
  • in the medial-lateral direction, the starting point is just lateral to the midpoint of the facet joint
  • if anatomic landmarks are not clear, c-arm fluoroscopy and a 19 gauge needle can be used to identify the pedicle starting point
  • a high speed cortical burr is used to mark starting point and just penetrate cortical surface
Pitfalls
  • The starting point will NOT be medial to a line down the center of the facet

8

Enter the pedicle(Thoracic)

  • insert a gear shift pedicle probe into the pedicle with the tip pointing laterally at the identified starting point
  • there is often a cancellous soft spot at the entry point into the pedicle (in smaller pedicles this may not be appreciable)
  • an alternative method is to use a small drill bit 2.0mm at slow speed which allows one to feel cortical versus cancellous bone, then repeat with a 3.2 mm drill bit to widen tract.

9

Advance the gear shift pedicle probe(Thoracic)

  • advance the probe using slight ventral pressure and axial rotation to a depth of 20 mm the transverse angle of insertion changes as one moves cephalad from 0 degrees in the lower thoracic region (T10-T12) to 10 degrees in the mid thoracic spine (T4- T9) to 15-25 degrees in the upper thoracic spine (T1 to T3)
  • the angle of insertion also needs to take into account the rotation of the vertebrae from the scoliotic deformity
  • after advancing to a depth of 20mm the gear shift pedicle probe is removed and the tract is probed with a sounding probe (ball tip probe)
  • medial, lateral, superior and inferior walls and the endpoint (floor) are palpated for any possible breech
  • if no breeches are appreciated, the gear shift pedicle probe is reintroduced pointing medially
  • the probe is advanced to the appropriate depth by rotating with slight ventral pressure
  • in adolescents this is typically around 35 mm but may vary significantly, and is often 30 in the upper thoracic spine
  • one should avoid using significant ventral pressure so that penetration of the anterolateral cortex of the vertebrae is avoided
Pearls
  • The transverse angle of probe/screw needs to take into account the amount of rotation from spinal deformity
  • If C-arm is used to find pedicle starting points, then amount of C-arm rotation is used to help determine desired trajectory

10

Probe the tract(Thoracic)

  • probe the tract using a flexible sounding probe (ball tip probe)
  • palpate the superior, inferior, medial and lateral walls and the endpoint (floor)

11

Measure the depth of the tract(Thoracic)

  • with the sounding probe tip on the endpoint of the tract, measure the depth by clipping a hemostat at the entry point
  • the sounding probe can then be held next to the screw to confirm the appropriate length
  • some surgeons follow this step by tapping the tract (the authors generally avoid this step)
  • if the pedicle tract was tapped, then probe the tract again for breech

12

Place the pedicle screw(Thoracic)

  • place the screw slowly in the orientation of the tract that was created

13

Stimulate screws(Thoracic)

  • below 6-8mA of stimulation current is considered a possible breech, though this figure varies.
  • remove screws stimulating below 6-8mA and check for breech by palpating with a ball tip probe from within the canal.
  • confirm position of screws with AP and lateral C-arm fluoroscopy
K

Rod Placement

P

1

Measure the length of the desired rod

  • use head adjuster to align all screw heads with a smooth cascade
  • use a malleable rod template or bovie cord to measure the length of the rod that is needed add 1-2 cm to the measure of the concave side to allow for distraction

2

Prebend the rods use french benders to prebend the rod to the appropriate sagittal contour

  • bend kyphosis through the thoracic spine
  • bend lordosis through the lumbar spine
  • neutral through thoracolumbar transition
Pearls
  • Overbend kyphosis on concave rod and underbend kyphosis on convex rod to help with derotation

3

Place concave rod first secure rod in pedicle screws with set screws, but leave set screws loose to allow for derotation maneuver

L

Correction of the Deformity

P
P

1

Plan reduction maneuvers

  • recognize that distraction across the concavity corrects scoliosis in the frontal plane, and simultaneously creates kyphosis in the sagittal plane
  • conversely compression across the convexity corrects scoliosis in the frontal plane, and simultaneously decreases kyphosis in the sagittal plane
  • thus, one may want to place the concave rod first in a typical hypo-kyphotic thoracic curve, but the convex rod first in the less common hyper-kyphotic curve

2

Derotation of the concave rod

  • vertebral column manipulators may be used at this time to rotate the vertebrae/thorax around the rod
  • rotating the rod 90 degrees (counterclockwise for typical right thoracic curve) turns the scoliosis into kyphosis and corrects the deformity in both coronal and sagittal planes
  • perform a 90 degree derotation maneuver with vise groups gripping the rod tightly
Pitfalls
  • Rod derotation does not equal thorax derotation
  • Therefore, it is important to consider using vertebral column manipulators either during or after rod derotation
  • Otherwise you may get correction in coronal and sagittal planes but worsen the degree of rotation

3

Tighten set screws to maintain the derotation

  • tighten set screws near apex of deformity to maintain derotation and to create starting point for distraction and compression

4

In situ or L-benders may be used for additional rod contouring

  • when using L benders lower hands to add kyphosis and raise hands to add lordosis

5

Perform additional distraction and compression for correction of the curve in the sagittal plane

  • distraction can then be performed through the apex of the curve on the concave side
  • if it is a double major curve, then additional compression may be performed on the convexity of the adjacent curve

6

Place the second rod

  • underbend kyphosis to help correct rib prominence

7

Secure second rod with set screws

Pearls
  • Consider loosening some set screws at apex of concave rod while seating convex rod if attempting to get additional correction

8

Evaluate reduction with C arm fluoroscopy

9

Assess shoulder height

  • With most thoracic curves there is a danger of the left shoulder ending up too high. This may be addressed by compression of the left screws, distraction of the right screws, or bending of the rods.

10

In general LIV should be horizontal

  • parallel to pelvis; possible exception= patients with leg length discrepancy
N

Wound Closure

P

1

Decorticate exposed bony surfaces at fusion levels

  • decorticate surrounding transverse processes, facet joints, and pars with burr

2

Irrigation and Hemostasis

  • irrigate copiously with normal saline
  • may use castile soap, dilute betadine or antibiotic in solution
  • address any areas of bleeding to minimize postoperative hematoma

3

Place autograft and allograft

  • pack posterolateral gutters with autologous/allograft graft
  • vancomycin powder is often added to the graft
Pearls
  • Author's preference is to add vancomycin powder to the bone graft and also place it above the fascia

4

Place hemovac drain

  • This may be placed above fascia, below fascia or both depending on surgeon preference
  • if there were osteotomies one may consider a deep drain to prevent intra-canal hematoma

5

Multilayer closure

  • close muscle layer with 1 vicryl
  • close fascia with 1-vicryl
  • need water tight closure

6

Superficial closure

  • subcutaneous with 2-0 vicryl
  • skin closure with buried 3-0 monocryl or PDS
  • dermabond and/or steristrips may also be used on the skin

7

Dressing

  • apply soft dressing

Postoperative Patient Care

O

Perioperative Inpatient Management

1

Writes appropriate admission orders

  • IV fluids
  • advance diet when return of bowel sounds or flatus (surgeon preference)
  • pain meds
  • antibiotics
  • continue for 24-48 hours
  • wound care
  • changes dressing on POD #2 or as needed
  • foley catheter out when ambulating
  • serial neurovascular exams
  • check appropriate labs

2

Appropriately orders and interprets basic imaging studies

  • standing PA and lateral thoracolumbar spine once ambulating well
  • review postoperative radiographs and identifies mal-positioned pedicle screws

3

Inpatient physical therapy

  • weight-bearing as tolerated, physical and occupational therapy
  • no heavy lifting and limited flexion/extension

4

Discharges patient appropriately

  • pain meds
  • wound care
  • schedule follow up 2 weeks after day of surgery
 

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