Perioperative Preparation In Scoliosis Surgery
Proper preparation of the patient is very necessary for the scoliosis surgery. If patient is on any nonsteroidal antiinflammatory agent, it should be discontinued before surgery. In case of females birth control pills should be discontinued 1 month before surgery [Increase the possibility of thrombophlebitis in the postoperative period].
Patient should be evaluated with x-rays, computed tomography, magnetic resonance imaging, and myelography for evaluation of spinal levels and to rule out conditions such as syringomyelia, diastematomyelia, and tethered cord.
In patients with severe curves pulmonary function studies usually are indicated.
Autologous blood donation in preoperative period in patients who are fit for autodonation is good option. Autologous donation reduces the the risks of homologous blood transfusion. Erythropoietin is another good but costly option.
Following routine gadgets are used for patient monitoring in scoliosis surgery
- Arterial line- continuous monitoring of blood pressure.
- Indwelling urinary catheter – monitor urinary output.
- Blood pressure cuff
- Esophageal stethoscope
- A pulse oximeter
Hypotensive anesthesia is the one in which arterial blood pressure is kept at 65 mm Hg. Hypointensive anesthesia is an effective way to reduce the loss of blood during surgery.
The cell saver is another method where one is able to save 50% of the red cell mass. However, cost could be a deterring factor.
Acute normovolemic hemodilution is another option to decrease loss of red cells. The maximum quantity of blood is withdrawn to reach to a level of 9 g/dL or higher after hemodilution and volume is maintained by crystalloid replacement. The surgery is conducted at normal blood pressure and diuresis of excess fluid is performed after surgery is finished followed by the transfusion of initially removed blood .
Somatosensory evoked potentials involve stimulation of distal sensory proximal to the surgical area and can alert the surgeon to possible alteration of spinal cord transmission. Preoperative baseline can be compared with one during the surgery. As it measures only the integrity of the sensory system, the use of motor evoked potentials has increased. The combination of motor evoked potentials and somatosensory evoked potentials can provide important information regarding the primary motor and sensory tracts within the spinal cord.
Stagnara wake-up test
Stagnara wake-up test, the anesthesia is decreased or reversed after correction of the spinal deformity. The patient is brought to a conscious level and asked to move both lower extremities. Once voluntary movement is noted, anesthesia is returned to the appropriate level, and the surgical procedure is completed.
Posterior Scoliosis Surgery
Posterior approach to the spinal column is the most commonly used for surgeries of idiopathic scoliosis. [Posterior means that incision is put on the back]
Following types of surgeries are performed on the scoliotic spine.
The long-term success of any operative procedure for scoliosis depends on a good arthrodesis.
The success of spinal arthrodesis depends on ability of the graft material to stimulate a healing process which in turn depends on
Surgical preparation of the fusion site
- Soft-tissue trauma should be minimal.
- Bed for grafting should be prepared well and avascular tissue should be removed
- Bone surfaces should be decorticated
A good bed exposes maximum surface area for vascular ingrowth and allows delivery of more osteoprogenitor cells [Cells that form bone cell precursors]
Systemic and local factors
- Good nutrition provides optimum condition for graft union.
- Any medical problem should be controlled.
- Smoking has been found to inhibit fusion significantly and should be stopped.
Autografts provide the best chances of union as it combines the osteogenic, osteoinductive and osteoconductive properties. Autograft taken from iliac crest is considered as “Gold Standard”. Another excellent source is rib obtained from a thoracoplasty.
Allografts have been shown to produce results equal to those of autogenous iliac crest graft in young patients.
They are routinely used in cases of paralytic scoliosis [Large amounts of bone graft are needed and the iliac crests often are small.
There are several graft substitutes like tricalcium phosphate, hydroxyapatite, and demineralized bone matrix but they are still under investigation
Bone graft generally does better under compression and is less effective with distraction.
Psuedorthrosis [literally -false joint] is failure of spinal fusion. But with modern surgical techniques, pseudarthrosis rate has been decreased.
Posterior Spinal Instrumentation
The goals of instrumentation in scoliosis surgery are to correct the deformity as much as possible and to stabilize the spine in the corrected position while the fusion mass becomes solid.
The fusion mass in a well-corrected spine is subjected to lower bending and tensile forces than is the fusion mass in an uncorrected spine
Spinal Instrumentation System
No Single device is the best choice for every surgeon or every patient.
Due to its disadvantages of need for distraction, laminar fractures, and loss of saggital contour, other instrumentation system have replaced it.
Multihook or posterior segmental instrumentation system with screws are are more commonly used now.
Posterior segmental spinal instrumentation systems have following advantages
- Multiple points of fixation to the spine
- Apply compression, distraction, and rotation forces through the same rod.
- Do not require any postoperative immobilization in most of the cases
- Better coronal plane correction and better control in the sagittal plane.
- Preserves normal contours of spine to good extent
The systems have, however, potential disadvantage of being bulky and complex and not many surgeons have much experience with them.
Posterior Thoracoplasty For Rib Hump In Scoliosis
Posterior thoracoplasty is a surgery for correction of rib hump in scoliosis though with newer surgical techniques and newer instrumentation, it is now done rarely.
The procedure is performed in prone position and the approach used is midline posterior. The procedure involves cutting of the ribs at the site of deformity.
Anterior thoracoplasty also aims at same correction.
Anterior Scoliosis Surgery
Anterior instrumentation and fusion is used in thoracolumbar and lumbar curves. It provides excellent derotation and correction of the curve in the coronal plane.
At some occasions, the deformity correction requires lesser number of motion segments to be fused than if done posteriorly.
For treatment to be effective the thoracolumbar or lumbar curve should be flexible. The thoracic curve should be nonstructural and reducible to 25 degrees or less on the bending films.
The child should be around 9 years of age.
Anterior instrumentation and fusion in thoracic curves is controversial.
In case of thoracolumbar curve, a thoracoabdominal approach is required. However in lumbar curves, a lumbar extraperitoneal approach can be used. Pedicle screws are used to instrument the spine.
Complications of Anterior Scoliosis Surgery
- Chylothorax – Collection of lymphatic fluid in pleural cavity following injury to lymphatics
- Injury to the ureter, spleen, or great vessels
- Retroperitoneal fibrosis
- Screw dislodgment
- Respiratory insufficiency requiring ventilatory support
- Collapse of lung alveoli
- Pneumothorax, hemothorax
- Urinary tract infection
Video Assisted Thoracoscopic Surgery
In this, the surgery is done with the help of thoracoscope [An endoscope that is inserted in the thorax from a portal and its imaging is used to guide the surgeon.
The Advantages of thoracoscopic surgery over open thoracotomy are
- Better illumination and magnification
- Lesser injury to the anatomical structures
- Decreased blood loss
- Better cosmesis
- Shorter recovery time
- Improved postoperative pulmonary function
- Shorter hospital stays.
The disadvantages are – technically demanding procedure, steep learning curve and requirement of the specialized equipment.
Video-assisted thoracoscopic surgery is indicated in
- Patients with compromised pulmonary function requiring anterior release
- Rigid curves requiring anterior release and posterior fusion
- When surgery is needed in young children to prevent crankshaft phenomenon
- and skeletal immaturity in patients in whom anterior surgery is needed to prevent the crankshaft phenomenon.
- Rigid thoracic idiopathic curves
Video-assisted thoracoscopic surgery is contraindicated in
- Inability to tolerate single-lung ventilation
- Respiratory insufficiency
- High airway pressures with positive-pressure ventilation
- Previous thoracotomy
Complications of video assisted thracoscopic surgery are
- Damage to lung tissue
- Dural tear
- Lymphatic injury [ Injury to thoracic duct]
Endoscopic Anterior Instrumentation
This technique allows anterior instrumentation of thoracic spine using a thoracoscopic approach. These technique are still being developed for getting results comparable to that of open thoracotomy.
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