معلومات عامة 2022, Dec, 23 | 12:00 am

Kyphectomy in Spina Bifida

 

Chapter 58

Kyphectomy in Spina Bifida

 

Richard E. McCarthy

 

DEFINITION

  • Kyphosis in the patient with myelomeningocele can occur at the thoracolumbar junction, the midlumbar spine, or the lum-bosacral junction.

  • The different types of kyphosis have some bearing on the treatment needed for the repair, but whether the origin is congenital, developmental, or paralytic, the consequences can be devastating for the child with this condition.

  • Skin breakdown over the apex of the kyphosis can develop deep wound infections and lead to central nervous system infections.

  • Secondary changes in other organ systems can create compromise in the gastrointestinal or genitourinary systems or even potentially disastrous kinking of the great vessels due to compromise in the abdominal height. Diminished absorption frequently occurs in the gastrointestinal tract, and renal calculi may develop from poor urinary drainage.

  • Secondary effects on the pulmonary capacity produce thoracic insufficiency syndrome because the abdominal contents are pushed into the thoracic cage. Added to this is a secondary thoracic lordosis cephalad to the kyphosis.

  • Bracing generally leads to problems from skin pressure and ultimately does not solve the problem.

    ANATOMY

  • The kyphotic angle can be gradual or acute.

  • The paraspinal musculature is partially innervated in a flexion position lateral to the bony ridges owing to lack of posterior migration from an embryologic origin. In this position, they contribute to forward flexion of the spinal column.

    • The bony ridges laterally in the area of the diastasis leave little bone for fusion mass on the posterior side of the vertebral column.

  • The midline defect from the original myelomeningocele characteristically is covered by a fragile dura separated from the overlying skin by a thin layer of subcutaneous tissue.

    • The soft tissue coverage is made worse by poor nutrition.

  • One of the most reliably formed vertebral structures is the sacral ala.

  • The great vessels generally do not follow the kyphotic contours into the kyphotic apex.

    PATHOGENESIS

  • Embryologically the notochord is covered dorsally by closure of the ectoderm over top of it, progressing in a cephalic to a caudal direction. In myelomeningocele, the closure is incomplete, usually at the caudal end.

  • Less common types of myelomeningocele occur in the thoracic and cervical area. Thoracolumbar, lumbar, and lum-bosacral kyphosis is the most commonly seen type and occurs because of lack of posterior migration of the ectoderm sur-

    rounding the notochord, leaving the neural placode in a vulnerable position, exposed at birth.

    • Congenital bony defects occurring in this area lead to an early-onset kyphosis that can pose significant problems for the neurosurgeon’s closure at birth. This has led some experts to encourage neonatal correction of the kyphosis.

  • With further growth and an upright sitting posture, the paraspinal musculature, which has formed in a lateral and anterior position, pulls the upper torso into a more kyphotic position, both actively through muscle contracture and secon-darily from gravity.

    • This can lead to further skin compromise and pressure in the soft tissues overlying the kyphosis.

    • Skin breakdown can be a serious problem over the kyphosis.

  • The C7 lateral plumb line shows the upper torso to be far out of balance in a forward-flexed posture, leading to thoracic insufficiency from the abdominal contents pressing under the diaphragm.

    • This can render the child a “functional quadriplegic” since he or she uses the upper extremities for balance and to unweight the diaphragm by pivoting on the extended arms for breathing purposes (marionette maneuver; FIG 1).

    • From a developmental standpoint, this can further limit the young child’s upper extremity interaction with his or her environment, which is essential for the development of normal intelligence.

      NATURAL HISTORY

  • The natural history of unpublished cases of severe kyphosis is one of thoracic compromise from insufficiency syndrome, progressive decline in pulmonary capacity, and death.

     

     

     

     

    FIG 1 • “Functional quadriplegia” in myelokyphosis; lumbar kyphosis with thoracic lordosis.

     

    1424

     

     

     

    PATIENT HISTORY AND PHYSICAL FINDINGS

    • A careful history and physical examination should elicit possible signs and symptoms of associated anomalies, including:

      • Chiari malformation

      • Tethered cord

      • Respiratory compromise

      • Gastrointestinal malabsorption

      • Urinary hydrostasis and lithiasis

    • Physical examination of the child should include flexibility tests of the curve by physically supporting the child under the armpits to suspend him or her against gravity. Bending back supine on the examining table can also indicate the extent of lumbar flexibility.

      IMAGING AND OTHER DIAGNOSTIC STUDIES

    • Standard radiographs, anteroposterior (AP) and lateral views of the full spine, in the upright sitting posture assess the effects of gravity upon the curve (FIG 2A,B).

      • Supine radiographs are helpful for visualization of bony definition.

      • Flexibility films with traction, manual push, or back bending over a bolster with a shoot-through lateral film, are helpful adjuncts.

    • CT scans, especially three-dimensional CT scans, offer the best delineation of the anatomy.

    • MRI is critical for assessment of the intrathecal structures and assessing for Chiari malformation, syringomyelias, and tethering (FIG 2C).

 

A

B

 

DIFFERENTIAL DIAGNOSIS

  • Congenital versus developmental kyphosis

  • Sacral agenesis

  • Charcot joints secondary to vertebral column breakdown across the apex of the kyphosis

    NONOPERATIVE MANAGEMENT

  • Bracing has no place in the treatment of this disorder.

  • Occasionally traction is helpful to stretch the kyphosis, especially in a developmental type to aid in correction at the time of surgery.

  • This can be done with cervical traction or halo traction, and some authors have promoted the use of this traction during the time of surgery to aid in the correction.

    SURGICAL MANAGEMENT

    Preoperative Planning

  • Vascular monitoring devices are an important adjunct during surgery, and either arterial lines or pulse oximeters on both feet are important to monitor blood supply to the lower extremities at the time of correction.

  • A great deal of tension can be placed on the aorta at the time of kyphosis realignment. Thus, arterial and central venous lines are necessary to monitor central pressure and allow for rapid medication administration.

  • Areas of skin breakdown should be addressed and healed prior to kyphectomy.

    • Preoperative planning may include assessment by a plastic surgeon and possible need for placement of tissue expanders in the posterolateral axillary margins to aid in skin closure at surgery (FIG 3).

  • As a part of the preoperative planning, all imaging studies are carefully reviewed to assess flexibility, the adequacy of the vertebral bodies to tolerate pedicle screws, and planning for which levels will need to be decancellized or removed.

    • It is recommended that these plans be recorded on a “blueprint” that can be placed on the operating room wall outlining the location of implants, osteotomies, and order of progression for the surgical plan.

  • Assessment by neurosurgery is necessary preoperatively regarding shunt functioning and review of the MRIs.

  • Preoperative antibiotics are essential, including gram-negative coverage for urinary pathogens. These are continued postoperatively for 6 to 12 weeks.

 

 

 

FIG 2 • A,B. A 13-year-old with myelokyphosis with diastasis beginning at T6 with 127 degrees of kyphosis. C. Preoperative MRI in a 9-year-old with myelomeningocele before undergoing kyphectomy with

C growing construct.

 

 

 

FIG 3 • Myelomeningocele in an 11-month-old with tissue expanders placed bilaterally before delayed closure and kyphectomy.

 

  • Nutritional status is maximized and may require hyperali-mentation via a gastrostomy tube button months ahead of surgery to maximize postoperative healing.

    Positioning

  • During positioning, careful padding with extra foam is essential to protect delicate skin during a prolonged operation.

  • Eye protection to guard against intraoperative ocular compromise and a spinal frame that allows for suspension of the abdominal structures will diminish the epidural vascular pressure.

  • Preoperative assessment of the hips is important to anticipate the intraoperative positioning, and if the flexion contractures about the hips are too severe, a preliminary release of contractures done a few weeks ahead of time may be necessary to allow for proper positioning of the legs at the time of the kyphectomy.

    Approach

  • The surgical incision may involve excision of compromised skin lesions or scars, although this is best addressed before surgery.

  • The previous incisions on a myelomeningocele back may not be midline or ideally placed.

    • The best skin incision for kyphectomy should follow the previous skin incisions to maximize blood supply to the skin edges at closure. Maximum skin and subcutaneous tissue coverage is important for good skin closure.

  • If a compromise in the quality of soft tissues is anticipated, then previously placed tissue expanders may be removed from the midline at closure and the expanded tissue brought to the midline.

  • There may be times when the poorly healed, convoluted scars from previous neurosurgical interventions may be harbingers of bacteria that will not promote adequate healing or may contribute toward postoperative infection. Preliminary excision of the scars by plastic surgery may afford the best defense against outside-in infections.

     

     

    TECHNIQUES

     

    INCISION AND LUMBAR DISSECTION

    • The incision—either straight or curvilinear—follows the previous scars. It is extended deep to the spinous processes in those sections where they exist.

      • The caudal portion of the incision is made to the level of the dura, with care taken to avoid laceration of the fragile dura.

    • The surgical plane is then deviated to the right and left side superficial to the dura while palpating for the lateral bony elements. The deep portion of the incision is directed toward the bone.

      • It is desirable to maintain as much subcutaneous thickness as possible.

    • If there are lacerations of the dura, it is best to stop and sew them as one proceeds since the thinned dura may re-

       

      quire a flap of adjacent tissue for a watertight closure. Sometimes it is necessary to sew in a piece of Duragen sealant to ensure a watertight closure.

      • Four-O Neurolon on a small needle in a running fashion works quite well for an incidental durotomy repair.

  • As one proceeds from distal to proximal in the lumbar spine, the lateral elements are palpated and with the use of electrocautery, the soft tissues are incised to bone.

  • The muscle and soft tissue attachments to the laterally positioned lumbar bones are released to reveal the underlying bony elements that embryologically would have progressed posteriorly to become the lamina and facets (TECH FIG 1A–C).

     

     

     

     

     

    T12

    Cord

    2 Dura mater closed at completion

    1 Initial excision of neural placode

     

    D

     

     

    A

     

    TEC

    sect plac bon are with elem the D.

    plac ing four the

     

    H FIG 1 • A. Intraoperative dis-

    ion with neuroplacode left in

    e and forceps placed on bilateral

    y ridges. B. Paraspinal muscles

    B

    C

     

    dissected away from the kyphosis, frequent irrigation of neural ents. C. In a different patient, kyphosis has been dissected out. The neuroplacode can be left in e, mobilized to one side by releas-nonfunctioning nerve roots over levels, or resecting to the level of

    diastasis and oversewing.

     

    • The rudiments of these bones can be visualized along with a transverse process at each level in the bony ridge of the diastasis.

  • The medial neural placode is left intact since it acts as third-space filler and padding for the implants.

  • There may be instances in which the neuroplacode has to be mobilized, and this is done by releasing nonfunctioning roots on one side and reflecting the dura laterally to gain access to the disc space and underlying vertebrae (TECH FIG 1D).

     

    THORACIC DISSECTION

    • Once the lumbar spine is dissected, the thoracic area is approached.

      • If one is contemplating a fusion of the thoracic spine, such as in a child over 8 years of age, full dissection out to the tips of the transverse processes should be accomplished.

    • If a growing rod construct is being used, such as in a child under age 8 years, this is done with minimal dissection so as to promote growth.

      • If the growing construct is desired, the muscle and soft tissue attachments are cleaned from the sides of the spinous processes as far as the facet joints.

         

  • One needs to be able to visualize the ligamentum flavum sufficiently to pass sublaminar wires for the Luque trolley portion of the “growing” construct.

    • Generally, four thoracic levels for wires are all that is necessary.

  • In the lumbar spine, soft tissues should be cleaned from bone sufficiently to allow for fusion between the lateral elements and to the sacrum.

     

    TECHNIQUES

     

    PEDICLE SCREW PLACEMENT

    • At this point in the operation, radiographic C-arm guidance is helpful for placement of pedicle screws.

    • The entrance point for the lumbar dysplastic pedicles is in a lateral position, with the pedicles directed obliquely toward the vertebral body (TECH FIG 2).

      • Bilateral screws can be obliquely placed for fixation.

    • Fixation to the pelvis can be done with multiple types of fixation devices, including S-rods, S-hooks, and iliac threaded bolts.

      • Fusion to the sacrum is essential to firmly plant the rod on the pelvis and allow for growth off the top of the rods in the thoracic spine.

    • The C-arm is used in both AP and lateral positions to confirm satisfactory placement of the screws in bone. Bicortical fixation is generally not necessary because of the strong fixation supplied by the triangulation of the screws.

    • Polyaxial screws are desirable through the lumbar segments.

       

       

       

       

       

      TECH FIG 2 • Screws in place and bilateral curettes in pedicles to decancellize at L3 before doing the same at T12.

       

      DECANCELLIZATION

    • Decancellization can be accomplished at multiple levels, leaving adequate vertebral levels for fixation and correction. Ideally, it is accomplished at one or two levels in a location that will leave sufficient midlumbar fixation points to push the vertebrae forward to create lordosis.

      • The levels chosen for decancellization are approached after screw placement, based on the preoperative planning.

    • The decancellization begins with a burr at the entrance to the pedicle. It continues with enlarging sizes of curettes, saving the bone for the fusion.

    • The inside of the vertebral body is completely cored out, and when bleeding points are encountered, the pedicle can be filled with FloSeal and if necessary further packed with some rolled Gelfoam to stop the bleeding.

       

  • Care is taken to avoid violating the posterior cortex of the vertebral body until the very end, since this is where the epidural vessels are most prolific.

    • The lateral margins of these vertebral bodies are removed, including the transverse process and posterolateral bone.

  • The decancellization should be thorough, leaving only the cortex. This is carried out bilaterally followed by im-plosion of the posterior cortex with an Epstein curette, pushing the bone fragments into the cavity of the vertebral body (TECH FIG 3).

    • Bleeding points are stabilized.

  • In most instances, decancellization alone at select levels is all that is necessary to gain the mobility for correction.

     

     

     

    TECH FIG 3 • Decancellization. A. Lateral view. B. Cross-sectional view. B

     

     

    TECHNIQUES

     

    A

     

    HORIZONTAL RESECTION

    T9

    L3

    T12

    A

     

     

    T9

    L4

    B

     

     

     

     

    • Occasionally, removal of a vertebral segment may be in- T9

      dicated. If so, it can be accomplished while maintaining the neuroplacode.

    • The vertebral section for removal in that instance would be taken from that section of the curve that is horizontal and cephalad to the apex of the kyphosis

      (TECH FIG 4). L4

       

      TECH FIG 4 • A. If bone is to be resected (due to extreme stiffness), this should be done in the horizontal section at the top of the kyphosis, not at the apex. B. After horizontal resection, the bone is pushed forward to realign. C. After resection,

      realignment and fixation are accomplished. C

       

      ROD PLACEMENT

    • Once these corrective maneuvers have been completed, rods linked to the sacrum can then be placed bilaterally to push the vertebral bodies anteriorly into a straight or preferably a lordotic position (TECH FIG 5A).

       

  • Through gradual approximation of the rod forward toward the thoracic fixation points, the lumbar segments are brought into alignment and the rods gradually tightened to the wires of the thoracic spine (TECH FIG 5B,C).

 

 

 

 

 

 

 

A B C

TECH FIG 5 • A. Bilateral rods are anchored to L4 and S-hooks in preparation for reduction. B. Decancellized levels are crushed by compressing adjacent screw heads. C. In a different patient, gradual reduction with wires and provisional tightening are accomplished using a growing construct. (continued)

 

 

D

E

 

TECH FIG 5 • (continued) D. Completed reduction in patient in A and B. Allograft and autograft have been applied to decorticated bone for fusion. E. Completed reduction in patient with growing construct in C.

 

  • Physiologic kyphosis can be contoured into the tho- ■ The final tightening should produce some distraction be-racic component of the rods to correct the thoracic tween the lowest lumbar segment fixation point and the lordosis. S-hooks pushed against the sacral ala (TECH FIG 5D,E).

  • Generally, the rods are left one level long at the top This will set the S-hooks in place securely.

to allow for growth in the thoracic spine. ■ Final contouring with the in situ benders can allow for

further lordosis of the lumbar spine if desired.

TECHNIQUES

ASSESSING AND MANAGING LOWER EXTREMITY HYPOPERFUSION

  • Frequently, the initial maneuvers for correction across the feet is unable to accommodate to the new position of kyphosis are accompanied by a decrease in blood flow to the spine, further decancellization or vertebral body re-the lower extremities. Therefore, it is important to do this moval will be necessary.

    corrective maneuver gradually in small increments. ■ This decision is based on the flow to the lower ex-

  • The baroreceptors in the aorta can accommodate to the tremities reflected in the pulse oximeter or arterial change in alignment and stretch. If the blood flow to the catheters in the feet.

CLOSURE

  • As part of the closure, it is important to grasp the paraspinal musculature with clamps to pull the muscles toward the midline by elevating and mobilizing the muscle layer with a Cobb elevator.

    • Sometimes release of the fascia on the posterior side of the musculature is necessary, and this is best done in the posterior axillary line with a vertical cut in the fascia.

  • The paraspinal musculature should be brought as close as possible toward the midline on both sides and sewn down (TECH FIG 6).

  • At least one and more likely two Hemovac drains should be left, one in the deep and one in the superficial layers, for drainage over 1 week to 10 days postoperatively.

  • Subcuticular closures can be used, but they should be re- TECH FIG 6 • The paraspinal muscle flaps are brought to mid-

inforced with external suture of some kind, either clips line for final closure. or interrupted nylon sutures on a temporary basis.

 

 

 

 

PEARLS AND PITFALLS

Evaluation

 

Preoperative preparation Intraoperative monitoring Preoperative preparation

 

Managing incidental dural tears

 

Preventing epidural bleeding Setting the S-hook

 

Postoperative care

  • The surgeon can assess flexibility of the curve by physically supporting the child under the armpits to suspend him or her against gravity. Bending back supine on the examining table can also indicate the extent of lumbar flexibility.

  • Areas of skin breakdown should be addressed and healed before kyphectomy.

  • Vascular monitoring of the lower extremities is a critical part of the intraoperative monitoring.

  • Preoperative antibiotics are essential, including gram-negative coverage for urinary pathogens. These are continued postoperatively for 6 to 12 weeks.

  • Four-O Neurolon on a small taper needle in a running fashion works quite well for an incidental durotomy repair. Duragen can be sewn over the repair, and occasionally the use of a sealant (Tusseal) is necessary.

  • Care is taken to avoid violating the posterior cortex of the vertebral body until the very end, since this is where the epidural vessels are most prolific.

  • The final tightening should produce some distraction between the lowest lumbar segment fixation point and the S-hooks pushed against the sacral ala. This will set the S-hooks in place securely.

  • All reasonable measures must be taken to avoid any pressure on the wound or extremities in the postoperative period. All areas of insensate skin must be protected from excessive pressure with frequent change in position on a soft surface. The dressings should be covered with a waterproof covering to protect against secondary contamination from stool.

 

 

POSTOPERATIVE CARE

  • For recovery, patients are placed on their back with an extra-thick foam on top of the mattress to avoid excessive skin pressure.

  • Logrolling is instituted 6 hours postoperatively and repeated every 2 hours.

  • Recovery occurs in the intensive care unit until the patient is sufficiently stable.

  • Although postoperative immobilization is not necessary, if desired it can be accomplished with careful molding of a bi-valved jacket with a Plastizote soft lining.

    OUTCOMES

  • Improved sitting

  • Improved respiratory function

  • Better blood supply to skin

    COMPLICATIONS

  • Skin breakdown

  • Infection, superficial or deep

  • Vascular compromise to feet with stretch on aorta

  • Loosening of spinal implants

  • Pseudarthrosis

 

REFERENCE

1. McCarthy RE. Myelokyphosis. Shriners Hospitals for Crippled Children, Symposium on Caring for the Child with Myelomeningocele, American Academy of Orthopaedic Surgeons, 2002.