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Hemivertebra Excision

Planning

B

Preoperative Plan

P

1

Identifies level of hemivertebra and plans levels for fusion

2

Preoperative MRI of entire spine obtained and reviewed

  • neurosurgeon consulted if indicated
  • if tethered cord is present that should be managed prior to hemivertebra resection
  • while detethering has been described as being done at a separate procedure or at the same time the authors preference is that this be done as separate operations.

3

CT scan obtained and reviewed

  • CT scan should be limited to the area of planned resection and fusion to minimize radiation
  • 3D CT scans are of great benefit in understanding the anatomy and preoperative planning
  • Template for placement of pedicle screws- estimate their length and diameter
Pitfalls
  • In some cases the anomaly posteriorly is not the same level as the hemivertebra anteriorly
  • Be sure to spend some time looking at 3D reconstructions and thoroughly evaluate the anatomy to avoid wrong level surgery
C

Room Preparation

P

1

Surgical instrumentation

  • pedicle screws of appropriate diameter and length based off of preoperative templating from 3D CT
  • hooks also available
Pearls
  • Authors generally use fixed angle screws as they have a smaller head than polyaxial screws to minimize hardware prominence

2

Room setup and equipment

  • table
  • Jackson spine or regular radiolucent flat top table
  • neuromonitoring
  • MEPs and SSEPs being monitored on both upper and lower extremities
  • C-arm
  • c-arm perpendicular to table

3

Patient positioning

  • prone with arms at 90° max abduction and flexion to prevent axillary nerve injury
  • pads on chest so that nipples are pointing midline straight down
  • pads at ASIS and padding on knees, hips and knees with slight flexion
  • abdomen free
  • foley in place
  • If performing anterior (transthoracic or retroperitoneal) approach, the patient should be in the lateral decubitus position with the convex side of the curve up

Technique

D

Anterior Approach (optional)

1

This is rarely done now but can be considered:

  • if there is a high level of concern about access to control bleeding in patients with other medical conditions
  • if the segment is lordotic making access to the hemivertebra more difficult
  • or if the surgeon does not have experience with circumferential surgery via a posterior only approach

2

If using this approach, position in lateral decubitus with break in the table or bump under the concavity

3

Transthoracic or retroperitoneal approach depending on location of hemivertebrae

  • See section on anterior spinal fusion for description of exposure
E

Posterior Approach

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
  • typically fusion is just one vertebral level above and below the hemivertebra

2

Make midline incision through region of planned fusion

  • make the midline skin incision
  • use bovie electrocautery through subcutaneous fat to expose fascia
  • expose to the cartilaginous caps of spinous process
  • preserve interspinous ligament at UIV and above and LIV and below (i.e. come down just lateral to interspinous through muscle to lamina)
  • Elevate the paraspinal muscle subperiosteally off of the lamina at the hemivertebra and levels of intended fusion
  • avoid exposure above or below the desired segment as this may result in inadvertent fusion posteriorly

3

Confirm level of the hemivertebra and intended fusion with imaging

  • Beware that at times the hemi-vertebrae may appear at different levels in the anterior and posterior spine, careful review of 3D CT can help define this. Compare intraoperative view to 3D CT.
F

Implant Placement

P

1

Pedicle screws or hooks are placed first because blood loss can make this difficult after hemivertebra excision

Pearls
  • As we hope to arrest anterior growth with these pedicle screws, and minimize plowing, use as long of screws as is safe

2

Place pedicle screws

  • Fixed angle screws are typically used because they are lower profile
  • Thoracic pedicle screws
  • burr through the cortex to mark the starting point
  • the starting point for screw placement is just lateral to the midpoint of the facet joint from medial to lateral
  • from cranial to caudad the starting point is at the level of the midpoint of the transverse process at T12 and gradually works superiorly to the superior aspect of the transverse process in the mid thoracic spine (T7-T9) and then back to the midpoint in the upper thoracic spine
  • the lenke probe is inserted to 20 mm facing laterally (alternatively a small 2.0 drill can also be used)
  • the tract is then checked with a ball tip probe for any cortical breeches
  • if there are no breeches then the lenke probe is reinserted facing medially and advanced to the anterior cortex (alternatively a 3.2 drill bit can be used in a similar fashion- taking care to stop before the anterior cortex)
  • the tract is again checked for breeches with a ball tip probe
  • if there are no breeches then the tract is measured with the ball tip probe by inserting the probe until it is on the anterior cortex, marking the depth with a finger or hemostat and holding the probe next to the screw
  • the screw is then inserted in the same trajectory
  • Lumbar pedicle screws
  • in the lumbar spine the pedicle is located at the junction of the pars interarticularis and the midpoint of the transverse process
  • a burr is used to mark the starting point
  • the screw is placed in the manner described above for thoracic pedicle screws
  • Evaluate screw position with C-arm fluoroscopy and perform EMG stimulation of screws
  • if stimulates at less than 6-8mA then tract is evaluated by removing screw and probing for any breeches and/or checking from within the canal

3

if pedicle screws cannot be placed, supralaminar or infra laminar hooks can be used at the levels above and below the hemivertebra

  • if the anatomy above or below the desired level does not permit instrumentation, instrumenting but not fusing one level longer for implant stability may be performed
  • although not intended inadvertent fusion at the extended level usually occurs
G

Hemivertebra Exposure

P

1

Begin midline and work laterally through the posterior elements of the hemivertebra using a kerrison rongeur

  • remove the ligament flavum and hemilamina
  • work out laterally at the level of the facets, remove the facets and optionally identify exiting nerve root above and below hemivertebra
  • remove the cortical bone that is dorsal to the pedicle and the transverse process with combination of rongeur and kerrison
  • protect the nerve roots through this process
  • control bleeding with bipolar cautery while avoiding injury to nerve roots.
  • gelfoam (with thrombin) is used to obtain hemostasis and cottonoids may used for protection of dura
  • at this point, all posterior elements of the hemivertebrae have been removed, with only the pedicle left

2

Dissect over the edge of the transverse process and down the lateral wall of the body using a Cobb elevator

  • one may dissect sub-periosteally around the lateral and anterior vertebrae. alternatively all dissection may be done from within the vertebral body.
  • then place a curved retractor anterolateral to the body for protection if sub-periosteal dissection is done
Pearls
  • If the hemivertebra is in the thoracic region remove the medial 4 cm or so of rib
  • This will allow the ribs above and below the removed rib to come together when the hemivertebrae is removed

3

Using a nerve root retractor and bipolar electrocautery to control epidural vessels, develop a plane medial to the pedicle wall

  • protect dura with the nerve retractor

4

on the contralateral side the facet is removed (i.e., on the concave side opposite the hemivertebra) both to allow correction and encourage fusion

H

Hemivertebra Excision

P
P

1

Develop a channel down the pedicle

  • at this point a nerve root retractor may be used to provide additional protection medially and a curved retractor may be used to protect anterolaterally
  • Care should be taken however to maintain the medial and inferior walls of the pedicle and work within them as much as possible to avoid inadvertent injury
  • use a combination of a diamond tip burr and curettes to develop a tract down the pedicle into the vertebral body
  • start with a small curette and gradually increase in size

2

Remove the body of the hemivertebra and the disc above and below the hemivertebra

  • It is important to maintain hemostasis at this step of the procedure. This is not a time to rush.
  • curved curettes and pituitary rongeur are used to remove disc material through the pedicle
  • no force should ever be directed towards the spinal cord. an "ice cream scoop" rotating motion of curettes is used to remove bone.
  • obtain a fluoro image with a curette in place to mark the extent of removal of disc and cancellous vertebral body ( to see how far medial, superior and inferior has been cleared)
  • it is common to not be as medial as one thinks they are, confirm that you are fully medial in the hemi-vertebrae with image.
  • remove disc to the point of vertebral endplate above and below the hemivertebrae to encourage anterior fusion and maximize correction
Pitfalls
  • Go slow on decancellation and maintain hemostasis
  • Bone wax may be pushed against bleeding bone with the back of curettes or other instruments
  • Gelfoam with thrombin may also be used to pack the space
  • Do not proceed with any further resection until bleeding is controlled

3

Resect the pedicle

  • resect pedicle in its entirety at this point using nerve root retractor to protect dura, the medial wall is resected last to protect the neural elements as long as possible
  • after removal of the pedicle, complete visualization of the nerve root above and below may be obtained to allow for protection during wedge closure, though this is not always necessary
  • Check to see if there are any remnants of the pedicle that can impinge on the nerve roots

4

Evaluate for any potential blocks to reduction that remain

  • the shape of the residual posterior elements should be contoured/resected to prevent blockage to reduction but should leave enough bone so after reduction the ends will be close to each other to encourage fusion
  • keep in mind hemi-vertebrae are often posterior lateral, and more resection is needed posteriorly than anteriorly to correct kyphosis

5

Place rod in anchors on concave side to provide some stability, but leave set screws loose to allow for correction. Unlike a VCR, the spine is not completely unstable at this point as the concave annulus is intact.

6

Place a posterior wall impactor just dorsal to the posterior wall and mallet this in an anterior direction to collapse the posterior wall of the vertebral body. this may be completed with an upgoing curette if needed.

  • after decancellating through the pedicle this should essentially be like an eggshell that can then be collapsed to allow for correction
  • significant bleeding may occur at this point, which is usually controlled with compression across the resected segment.
Pearls
  • In some cases the impactor may become trapped when the posterior wall collapses
  • In this case have assistant hold impactor steady and place convex rod
  • Then distract slightly to allow smooth/safe removal of impactor and avoid pulling hard on impactor in direction of cord

7

Alternatively the vertebral body and disc can be removed piecemeal through an anterior approach

I

Correction of the spinal deformity by closure of the hemivertebra wedge resection

P

1

Place rod in anchors on convex side

2

When enough compression is placed across pedicle screws to closes the resected area, the pedicle screws often plow and lose purchase. to prevent this a third rod with hooks on ribs or lamina can withstand most of the compressive force and protect the pedicle screw purchase.

  • In cases of thoracic hemivertebra one can place a third rod with a down going rib anchor on the rib of the UIV and an up going rib anchor on the rib of the LIV
  • In cases of lumbar hemivertebra one can place a third rod with a down going laminar hook on the UIV and an up going laminar hook on the LIV

3

Closure of hemivertebra wedge resection

  • correction can be achieved partly by pushing the spine, body, or vertebral elements directly
  • Secure the set screws on the third rod to maintain the correction achieved
  • Distract the concave rod
Pearls
  • A third rod on ribs or lamina can be used to close down the wedge from the hemivertebra resection and obtain correction
  • Most of the compressive force should be on these hooks

4

The goal should be nearly 100% correction of coronal and sagittal deformity in most cases, which is often obtained by multiple compressions and distractions over time while running MEPS.

5

Evaluate coronal and sagittal balance with C-arm fluoroscopy

  • torque set screws to final tighten once correction has been optimized

6

Decorticate posterior elements with a burr at the levels of intended fusion

7

If using an anterior approach one can remove bump or break table at this step to facilitate correction

J

Wound Closure

1

Irrigate and place bone graft

  • flush out spine with saline bulb irrigation
  • can use betadine wound lavage or vancomycin powder to decrease infection risk
  • obtain hemostasis
  • place allograft/autograft at levels of intended fusion
  • consider hemovac drain (to prevent compressive hematoma around cord)

2

Close Fascia

  • close fascia with 0-vicryl
  • need water tight closure/decrease dead space for hematoma
  • authors place vancomycin powder both in the bone graft and above the fascial layer once closed

3

Superficial closure

  • subcutaneous with 2-0 vicryl
  • skin closure with buried 3-0 monocryl
  • this can be reinforced with nylon sutures and/or surgical glue

4

Dressing

  • place soft dressing (attending preference)

5

Place most small patients in a TLSO brace for three months

  • recommended if there is any concern about strength of fixation
  • alternatively, in some very young patients may consider a cast

Patient Care

L

Perioperative Inpatient Management

1

Writes appropriate admission orders

  • IV fluids
  • advance diet when return of flatus
  • pain meds
  • antibiotics
  • continue for 24-48 hours
  • wound care
  • serial neurovascular exams
  • check appropriate labs

2

Appropriate medical management and medical consultation

3

Inpatient physical therapy

4

Discharges patient appropriately

  • pain meds
  • wound care
  • schedule follow up in 2 weeks
M

Postoperative Evaluation and Management

1

Obtain focused history and performs focused exam

  • interpret neurological exam

2

Appropriately orders and interprets advanced imaging studies when indicated

  • CT scan

3

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

  • postop: ~ 3 month postoperative visit
  • remove the brace/cast
  • advance spine restrictions and activity levels
N

Advanced Evaluation and Management

1

Capable of surgically treating simple complications

  • drainage of hematoma
  • debridement of infection
 

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