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SICOT e-Newsletter

Issue No. 59 - August 2013

Editorial

How I correct Adolescent Idiopathic Scoliosis

Nanjundappa S. Harshavardhana
SICOT Associate Member - Philadelphia, United States

John P. Dormans
SICOT Active Member - Philadelphia, United States






Introduction


Scoliosis is characterized by frontal plane curvature of spinal column with axial rotation of vertebrae producing a rib-hump deformity. Adolescent idiopathic scoliosis (AIS) is the most common spinal deformity and is seen most commonly in girls (male:female being 1:10). It is most commonly right-sided and most frequently affects the thoracic spine. AIS can produce unacceptable cosmetic deformity with poor body self-image which may need surgical intervention to prevent curve progression, arrest deterioration in pulmonary function and enhance self-esteem.

Intensive investigations have been undertaken over the past decade to identify genes that predispose an individual to develop AIS. It is a multifactorial condition and several genes have been implicated1,2.


Clinical Evaluation

A typical AIS curve is convex to right with its apex at T8-9 disc/T9 body with loss of thoracic kyphosis (lordoscoliosis). The most commonly used classification in the contemporary era for AIS is that of Lenke and curves are divided into six types3. Thorough clinical examination/detailed neurological evaluation and radiographs are mandatory for all patients. History of back pain is evaluated and all patients fill a new patient pain profile sheet with pictorial representation/description of their pain. Superficial abdominal and deep tendon reflexes should be elicited in all patients as there may be co-existent intra-spinal anomalies. Supine bending views against a bolster placed at the apex of the curve on the convex side are also undertaken to evaluate flexibility. We have a low threshold to get an MRI for all patients at our institute. The presence of any atypical features warrant a complete neurological examination with MRI scans to rule out intra-spinal anomalies4. Coned down view of lumbo-sacral junction is done to rule out spondylolysis.

Mild deformities (<300 are observed or braced) and surgery reserved for curves that measure ≥500. Rigid curves may need an anterior release prior to posterior instrumented spinal correction and fusion. Progression of curve despite bracing and unacceptable cosmetic deformity esp. with Riser Gr. 0-II would be indications for surgery.


Surgical Technique

The patient is induced under general anaesthesia with endo-tracheal tube and placed prone on a Jackson table with adequate padding of all bony prominences and pressure areas with face resting on head holder with no pressure on eyeballs. Particular care is taken not to hyperabduct arms as it may stretch brachial plexus in prolonged prone positioning5. Safety is of paramount importance and neuro-monitoring is mandatory for all patients. We routinely use multi-modal neuro-monitoring (i.e. TcMEP - trans-cranial motor evoked potentials and SSEP – somatosensory evoked potentials) to monitor cord function especially during corrective maneuvers. A 50% drop in amplitude of TcMEP is considered as true positive. SSEPs monitor the sensory tracts. TcMEP changes normally predate SSEP changes by 5 minutes which is extremely helpful6. Hypotensive anaesthesia with MABP (mean arterial blood pressure) of 60mm Hg is desired for exposure and during instrumentation to minimize blood loss. However, prolonged hypotension could cause spinal cord ischemia and is not used for congenital spinal deformities due to precarious cord vasculature7.


Surgery

The fusion levels (i.e. upper & lower instrumented vertebrae) are decided from radiographs and a midline skin incision is made. The spine is exposed by subperiosteal dissection and cell saver is used to process intra-op blood loss. Surgical packing, gel-foam, bone wax and hemostatic matrix are used liberally to keep blood loss to a minimum. A marker is placed over spinous process and c-arm shot is taken to confirm the vertebral level. Intra-operative c-arm image intensifier is then used to aid in pedicle screw insertions. Our preference is to use mostly pedicle screw based constructs with use of hooks and wires especially in cranial end of instrumentation8.


Correction

Once all the anchors are secured, a Co-Cr or ultra-strong stainless steel rod of 5.5 – 6.0mm diameter is cut to appropriate length and bent to normal contours in sagittal plane. We sometimes also perform differential rod contouring (concave rod – normal kyphosis and convex rod – hypokyphosis) to aid in ease of reduction and correction. The spinal deformity (sagittal lordosis/coronal scoliosis and axial rotation) is corrected by a combination of maneuvers. We perform selective rod rotation with subsequent coupled derotation to restore spinal balance and alignment. The concave rod is first inserted cranio-caudally and secured to all anchors by provisional tightening. This corrective rod is then rotated by 900 and spine is gradually approximated to the rod from either ends towards the center (i.e. apex of deformity in sagittal plane). The stabilizing convex hypokyphotic rod is then attached to its anchors and spine pushed towards midline (cantilever forces and translation) as the rod is secured to the anchors. Coupled derotation is then performed at the apex of deformity to correct axial rotation with compression of screws on convexity of curves (Fig. 1). Final tightening is then performed and all anchors are double-checked. Judicious use of polyaxial reduction screws ensures safe instrumentation without any pull-out of vertebral anchors. Coupled direct vertebral derotation is very powerful in correcting rib-hump deformity and has virtually eliminated the need for costoplasty. Ponte osteotomies are also performed to enhance restoration of thoracic kyphosis, overall sagittal balance and improve fusion rates.

Once the scoliosis is corrected, the allograft strips are laid over posterior elements over instrumented area mixed with allograft paste to achieve satisfactory inter-facetal, inter-laminar and inter-transverse fusion. We do not routinely use crosslinks. 500mg of vancomycin powder is locally applied over the exposed spine and instrumentation prior to suturing deep fascia9. The wound is then closed in layers with the placement of the drain superficial to deep fascia10. Fig. 2 shows radiographs of an index Lenke I AIS operated by the senior author (JPD).


Post-op management

The drain is removed in 24-48 hours when output is <30cc/24 hours. Most patients are mobilized from post-op day 2 when they transfer and sit in a chair for a few hours. Most of the patients walk by the 2nd to 3rd post-op day and are discharged home by the 4th-5th post-op day. Some patients may continue to wear orthosis (spinal brace) post-operatively for comfort. All patients are seen in office (clinic) at 1 week, 6 weeks, 3 months, 6 months and at 12 months post-op. Annual follow-up thereafter is undertaken until they complete growth or are discharged from paediatric care as adults to ensure their recovery from the surgery is without any untoward events.


Summary

Surgery for AIS improves cosmesis and enhances self-esteem in a vulnerable group of adolescents. Intra-operative neuro-monitoring, hypotensive anaesthesia during exposure and instrumentation with normo tension during the correction maneuver with a meticulous surgical technique and attention to detail have made scoliosis surgeries very safe. Meticulous soft tissue handling, subperiosteal dissection, wound closure and placement of a drain have all contributed to successful patient outcomes.
 

References
  1. Genome-wide association studies of adolescent idiopathic scoliosis suggest candidate susceptibility genes. Sharma S, Gao X, Londono D, Devroy SE, Mauldin KN, Frankel JT, Brandon JM, Zhang D, Li QZ, Dobbs MB, Gurnett CA, Grant SF, Hakonarson H, Dormans JP, Herring JA, Gordon D, Wise CA. Hum Mol Genet. 2011 Apr 1;20(7):1456-66.
  2. Whole Exome Sequencing of Familial Adolescent Idiopathic Scoliosis Uncovers Novel Mutations. Dormans JP, Sasson A, Salley FJ, Kim CE, Deliard S, Talarico J, Chiacacci RM, Hakonarson H, Grant SFA. Abstract submitted to AAOS. 2013.
  3. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. Lenke LG, Betz RR, Harms J, Bridwell KH, Clements DH, Lowe TG, Blanke K. J Bone Joint Surg Am. 2001; 83-A(8): 1169-81
  4. Use and outcome of MRI in the surgical treatment of adolescent idiopathic scoliosis. Diab M, Landman Z, Lubicky J, Dormans J, Erickson M, Richards BS; Members of the Spinal Deformity Study Group. Spine (Phila Pa 1976). 2011; 36(8): 667-71. 
  5. Prevention of positional brachial plexopathy during surgical correction of scoliosis. Schwartz DM, Drummond DS, Hahn M, Ecker ML, Dormans JP. J Spinal Disord. 2000; 13(2): 178-82. 
  6. Neurophysiological detection of impending spinal cord injury during scoliosis surgery. Schwartz DM, Auerbach JD, Dormans JP, Flynn J, Drummond DS, Bowe JA, Laufer S, Shah SA, Bowen JR, Pizzutillo PD, Jones KJ, Drummond DS. J Bone Joint Surg Am. 2007; 89(11): 2440-9.
  7. Update on congenital spinal deformities: preoperative evaluation. Chan G, Dormans JP. Spine (Phila Pa 1976). 2009; 34(17): 1766-74. 
  8. Fixation points within the main thoracic curve: does more instrumentation produce greater curve correction and improved results? Sanders JO, Diab M, Richards SB, Lenke LG, Johnston CE, Emans JB, Sucato DJ, Erickson MA, Bridwell KH, McCarthy RE, Sarwark JF, Dormans JP; Spinal Deformity Study Group. Spine (Phila Pa 1976). 2011; 36(21): E1402-6. 
  9. Adjunctive Vancomycin Powder in Pediatric Spine Surgery is Safe. Gans I, Dormans JP, Spiegel DA, Flynn JM, Sankar WN, Campbell RM, Baldwin KD. Spine (Phila Pa 1976). 2013 Jun 11 [Epub ahead of print].
  10. The use of postoperative subcutaneous closed suction drainage after posterior spinal fusion in adolescents with idiopathic scoliosis. Blank J, Flynn JM, Bronson W, Ellman P, Pill SG, Lou JE, Dormans JP, Drummond DS, Ecker ML. J Spinal Disord Tech. 2003;16(6): 508-12.
 

Fig. 1: Pre- and Post-op X-rays (Case 1)


Fig. 2: Pre- and Post-op X-rays (Case 3)


Fig. 3: Pre- and Post-op X-rays (Case 2 – Double structural curve)