Sarwahi et al. Scoliosis 2011, 6:16
`http://www.scoliosisjournal.com/content/6/1/16
`
`M E T H O D O L O G Y
`
`Open Access
`
`Minimally invasive scoliosis surgery: an innovative
`technique in patients with adolescent idiopathic
`scoliosis
`Vishal Sarwahi*, Adam L Wollowick, Etan P Sugarman, Jonathan J Horn, Melanie Gambassi and Terry D Amaral
`
`Abstract
`
`Minimally invasive spine surgery is becoming more common in the treatment of adult lumbar degenerative
`disorders. Minimally invasive techniques have been utilized for multilevel pathology, including adult lumbar
`degenerative scoliosis. The next logical step is to apply minimally invasive surgical techniques to the treatment of
`adolescent idiopathic scoliosis (AIS). However, there are significant technical challenges of performing minimally
`invasive surgery on this patient population. For more than two years, we have been utilizing minimally invasive
`spine surgery techniques in patients with adolescent idiopathic scoliosis. We have developed the present
`technique to allow for utilization of all standard reduction maneuvers through three small midline skin incisions.
`Our technique allows easy passage of contoured rods, placement of pedicle screws without image guidance, and
`allows adequate facet osteotomy to enable fusion. There are multiple potential advantages of this technique,
`including: less blood loss, shorter hospital stay, earlier mobilization, and relatively less pain and need for pain
`medication. The operative time needed to complete this surgery is longer. We feel that a minimally invasive
`approach, although technically challenging, is a feasible option in patients with adolescent idiopathic scoliosis.
`Although there are multiple perceived benefits, long term data is needed before it can be recommended for
`routine use.
`
`Introduction
`Minimally invasive spine surgery is becoming more
`common for the treatment of multilevel pathology,
`including adult lumbar degenerative disorders [1-3]. The
`next logical step is to apply minimally invasive surgical
`techniques to the treatment of adolescent idiopathic
`scoliosis (AIS). However, there are significant technical
`challenges of performing minimally invasive surgery on
`this patient population. In contrast to adult degenerative
`scoliosis, the curves in AIS patients are much larger
`(usually 45-50° or more), the number of levels instru-
`mented are longer (7-13), the deformity exists in three
`planes, and the vertebral rotation can be significant. Pla-
`cement of pedicle screws (14-26 screws) also increases
`radiation exposure for both the patient and the surgeon
`[4-6]. In patients with double major curves, passing a
`rod that is contoured in the normal sagittal profile
`
`* Correspondence: vsarwahi@montefiore.org
`Department of Orthopaedic Surgery, Montefiore Medical Center, Albert
`Einstein College of Medicine, Bronx, NY, USA
`
`(thoracic kyphosis and lumbar lordosis) is a challenge in
`and of itself.
`The ultimate goal of the surgical management of AIS
`is to obtain an adequate fusion. In contrast to the adult
`population, an anterior approach is often not utilized in
`AIS patients, either for release or for fusion [7]. Thus, it
`is imperative that any surgical technique for AIS allows
`for adequate fusion at the facet joint. In the context of
`minimally invasive surgery, obtaining sufficient surface
`area for arthrodesis can be challenging. Bone morpho-
`genic protein can be utilized, but is an off-label indica-
`tion for this age group as well as for this type of surgery.
`Two other important issues in considering minimally
`invasive approaches to AIS are the length and type of
`skin incision as well as the reduction maneuvers
`employed for deformity correction. The standard stab
`incision for placement of minimally invasive or percuta-
`neous pedicle screws cannot be utilized in adolescent
`patients, as fourteen to twenty six stab incisions in the
`back can be quite disconcerting for a young patient.
`Additionally, surgeons treating large spinal deformities
`
`© 2011 Sarwahi et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
`Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
`any medium, provided the original work is properly cited.
`
`Medtronic, Inc. MSD 1047
`
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`typically have the ability to utilize multiple reduction
`maneuvers, including rod translation, rod derotation, in
`situ bending, direct vertebral rotation, and spine transla-
`tion [8,9]. Only limited reduction maneuvers can be car-
`ried out with the present minimally invasive spine
`surgery instrumentation systems [10]. These instrumen-
`tation systems fall short in their ability to reduce a con-
`toured rod into the pedicle screw heads. This is
`especially true when attempting to restore normal thor-
`acic kyphosis, as a contoured rod often sticks above the
`screw head.
`The purpose of this study is to detail a new technique
`for minimally invasive posterior spinal fusion which lim-
`its incision length as well as soft-tissue dissection while
`allowing for deformity correction.
`
`Materials & methods
`Since May, 2008, we have been utilizing minimally inva-
`sive spine surgery techniques in patients with adolescent
`idiopathic scoliosis. The presented technique allows for
`utilization of all standard reduction maneuvers through
`three small midline skin incisions. This technique allows
`easy passage of contoured rods, placement of pedicle
`screws without image guidance, and adequate facet
`osteotomy to enable fusion.
`
`Surgical Technique
`Three two-inch-long midline skin incisions are made for
`instrumentation of eleven to thirteen segments. Three
`to four segments (6-8 pedicle screws) are instrumented
`per skin incision. Intraoperative fluoroscopy is used to
`determine the length and location of these incisions.
`Although a single straight midline incision can be made,
`three smaller incisions are often more cosmetically
`appealing to patients. The skin is undermined to either
`side of midline in order to allow for the placement of
`bilateral pedicle screws. In the lumbar spine the facet
`can be manually palpated. A stab incision in the fascia
`is made directly over the facet. Thereafter, the muscle
`fibers are split bluntly in line with their fibers using a
`small cobb elevator, or with an insulated tipped electro-
`cautery, to expose the joint (Figure 1). A small Gelpi
`retractor provides excellent exposure and a fiber optic
`light source is used for illumination. The Gelpi retractor
`also allows for adjustment of tissue tension, which
`decreases muscle necrosis and spasm. Once the facet
`joint is exposed, facetectomy is performed with a high
`speed burr. Stab incisions are made for placement of
`pedicle screws at all levels. At times, the stab wounds
`become contiguous, rendering the fascial and the muscle
`exposure akin to a Wiltse approach [11].
`In the thoracic spine the inferior facet usually lies at
`the level of the tip of the spinous process of the superior
`vertebra (Figure 2). On the concave side, we make a stab
`
`Figure 1 “The L2 facet visualized through a stab incision in the
`fascia.” The left L2 facet visualized through a stab incision in the
`fascia. The Gelpi is serving as a retractor.
`
`incision approximately one centimeter lateral to the
`midline at the level of the spinous process tip, whereas
`on the convex side we make a stab incision approxi-
`mately 1.5 cm lateral to the midline. When in doubt, we
`use C-arm to confirm the location of the pedicle. We
`take advantage of the thoracic spine anatomy in locating
`the facet joints at the level above and at the level below
`- the overlapping laminae allow for contiguous exposure
`of these facets. Under direct visualization and illumina-
`tion, the facet joint is osteotomized using a combination
`of a quarter-inch osteotome and a high-speed burr.
`Adequate excision of the facet joint is carried out to
`ensure a solid fusion. The facet joint of the uninstru-
`mented intervening segment between skin incisions is
`
`Figure 2 “Localization of the facet joint.” Localization of the facet
`joint is as follows. The spinous process of the thoracic spine usually
`lies at the level of the caudal facet joint. Thus, a T6 spinous process
`is approximately at the level of the T7-T8 facet joint. This helps in
`localization of the thoracic facet. Also, notice the overhang which
`allows for easy dissection of the facet joint above, and the facet
`joint below.
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`also exposed in the manner previously described. The
`facet joint is osteotomized and prepared for fusion. This
`area is left uninstrumented, but bone graft is placed to
`facilitate arthrodesis. Exposure of this joint can usually
`be accomplished by undermining the skin and extending
`the fascial incision.
`Freehand anatomic placement technique is utilized for
`pedicle screw insertion, as has previously been described
`[12]. The facet osteotomy and the exposure allow for
`easy identification of the anatomic entry point. The
`entry point in the thoracic spine is usually the point of
`intersection between the midline of the facet joint and
`the upper-third of the transverse process. In the lumbar
`spine the entry is the intersection point between the
`midline of the transverse process and the midline of the
`facet joint (Figure 3). This is often at the base of the
`superior facet. Complete exposure of the transverse pro-
`cess is usually not needed for identification of this land-
`mark, but may be carried out if desired. Alternatively,
`the pedicle screw can be placed using fluoroscopy gui-
`dance. We prefer to place all screws on one side first.
`This allows for easy mobilization of the skin. It is typi-
`cally not possible to place both screws in each vertebra
`simultaneously due to the limited skin incision.
`We utilize the DePuy 5.5 EXPEDIUM® (5.5 mm rod,
`stainless steel) pedicle screw instrumentation system.
`Our preference is to use two uniaxial reduction screws
`and one MIS screw with an open connector per skin
`incision (Figure 4). The reduction screws have signifi-
`cant advantages. They allow for easy reduction of the
`rod and/or the spine to achieve correction of scoliosis
`deformity in two planes. Since the extended tabs stick
`out above the fascia, they allow for easy passage of the
`rod into the screw heads. Thus, the rod can be passed
`
`Figure 3 “The entry point to the pedicle.” In the lumbar spine,
`the base of the superior facet often overlies the entry point to the
`pedicle of the same level. The superior facet can be rongeured off
`to expose the bleeding cancellous bony area, which marks the
`entry site to the pedicle.
`
`Figure 4 “Order of screw placement.” The order of screws
`placement for two segments (7 Spinal levels) is shown from left to
`right representing inferior to superior. Each segment consists of
`three levels with a skipped level in between each segment. Two
`standard reduction screws (T10, T9) are instrumented at the inferior
`levels followed by a MIS reduction screw (T8) at the superior level.
`The same pattern is seen in the T4-T6 segment. A rod reduction
`device is shown on the T9 screw which can facilitate seating of the
`rod when necessary. Open connectors are pictured extending from
`the MIS screws.
`
`under direct visualization and the screw heads can be
`manipulated for easier passage. The extended tabs also
`serve as soft tissue retractors. Prior to the insertion of
`the pedicle screw, the fusion site is prepared. Local
`autograft (from the facet joint osteotomy) as well as a
`small BMP-enriched sponge or other bone graft substi-
`tute is placed in the fusion bed. We usually do not per-
`form EMG stimulation of the pedicle screws, but SSEP
`and transcranial MEP monitoring are employed
`throughout the case.
`Two rods, cut to appropriate length, are contoured in
`the normal sagittal plane to reproduce desired thoracic
`kyphosis and lumbar lordosis. The rod is inserted
`cephalad to caudad (Figure 5). This is an important
`safety step, as the overlapping laminae in the thoracic
`spine prevent an inadvertent entry into the spinal canal.
`The reduction screws are capped as the rod advances,
`and the screw heads can be manipulated for rod pas-
`sage. The open MIS connectors serve as a post against
`which the rod can be maneuvered. A vise-grip pliers is
`utilized to hold the rod as it provides a strong grip and
`easy manipulation. A rod pusher can be utilized to
`translate the rod onto the screw heads. Alternatively,
`the assistant can directly apply translation force to the
`chest wall to push the spine over to the rod. We prefer
`to utilize rod translation maneuvers, however, a CD rod
`derotation technique can also be utilized with the help
`of a vise-grip. As the rod passes from one wound to the
`next, one must confirm that the rod is lying beneath the
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`Figure 5 “Rod introduction from cephalad to caudad.” The rod
`is being introduced cephalad to caudad. Notice the open-ended
`MIS connector at the proximal and distal incisions. These serve as
`posts against which the rod can be manipulated and also enable
`easy visualization of the rod.
`
`fascia. The rod can be manually palpated in the distal
`wound (Figure 6), which helps to properly direct the
`rod.
`Once the rod is seated in all pedicle screw heads, the
`rod is manipulated to restore the sagittal contour of the
`spine (Figure 7). Caution must be given to prevent over-
`rotation of the rod, as this has the potential to reverse
`the thoracic kyphosis. This mistake is more likely to
`occur with a rod derotation maneuver, as the sagittal
`contours of the rods are difficult to appreciate through
`small skin incisions. The set screws are now sequentially
`tightened, and the rod is formally seated. The same
`maneuver is now carried out on the opposite side
`
`Figure 6 “Passing the rod along the spine.” As the rod is passed
`along the spine, it can be manually palpated, as show in the
`picture, and guided as necessary. Notice the kyphotic bend of the
`rod which is being passed to maintain the desired sagittal profile.
`
`Figure 7 “Rod manipulation with a vise-grip for larger
`deformity.” The vise-grip allows a stronger manipulation of the rod,
`which is often needed in larger deformities. It can also allow for a
`CD rod-derotation maneuver. Notice that the rod has almost
`completely disappeared from the picture. Usually the rod is longer
`than needed, and at this point, can be cut to appropriate length.
`Also notice the sagittal contour of the rod has been appropriately
`maintained. The extra open MIS connectors used here are an
`occasional variation in technique.
`
`following the placement of pedicle screws. Appropriate
`compression and distraction force can also be carried
`out. This can be easily accomplished through the mid-
`line skin incisions. In situ rod bending can also be car-
`ried out, but is not our preferred technique. A direct
`vertebral rotation maneuver is then carried out off the
`concave-side screws. Triangulation technique is difficult
`to achieve, as the skin incision limits access to both
`sides simultaneously. This can, however, be easily car-
`ried out with a straight midline incision approach. Clo-
`sure is fairly rapid, and is carried out in a layered
`fashion. We do not utilize drains. In our more recent
`cases, we excise the wound edges to prevent hyper-
`trophic scar formation (Figure 8). While the patient is
`still on the operating table, anteroposterior and lateral
`X-rays are taken to confirm adequate correction in both
`planes. Our postoperative protocol is fairly routine. We
`do not routinely use a brace. Patients must be able to
`walk up a flight of stairs prior to hospital discharge, and
`are to remain out of school for six weeks to three
`months. At two weeks post-op, patients may go outside
`their residence, and at three weeks post-op, they may
`travel short distances. We allow activity as tolerated
`within the limits of pain. Patients can return to gym
`class between four and six months post-op, and may
`participate in contact sports and perform heavy lifting
`after six months. We prefer to use Ketorolac (Toradol,
`Roche Laboratories, Nutley, NJ) rather than morphine
`for analgesia purposes.
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`left-sided main thoracic (T8-L2) and a 38° (T4-T8) upper
`thoracic curve. The patient can be seen to have a 24° thor-
`acolumbar kyphosis (Figure 9). The classic 3-3-3 pedicle
`instrumentation pattern (three levels instrumented per
`skin incision) was utilized. Postoperative X-rays are shown
`(Figure 10 &11). 6-0 × 40 mm screws were used at all
`levels and were placed using a freehand anatomic techni-
`que. Postoperative CT-scan is used to evaluate adequacy
`of pedicle screw placement (Figure 12).
`In our second case a 13.5 year-old girl with a 57°
`right-sided main thoracic curve (T6-T12) underwent
`minimally invasive surgery for correction of her spinal
`deformity. A slightly different variation of screw place-
`ment was utilized (Figure 13). Four levels were instru-
`mented through the distal incision, while three levels
`were instrumented through the proximal and middle
`incisions. The postoperative X-rays demonstrate this
`variation and show good correction in the coronal and
`sagittal planes (Figure 14 &15).
`Two-year follow-up data for 7 patients with AIS who
`underwent posterior spinal fusion with our minimally
`invasive technique was obtained. The average age in this
`cohort was 15.6 (range: 12.6 - 20.5) years. 4 patients had
`Lenke type 1 curves, 2 had Lenke type 2 curves, and 1
`
`Figure 8 “The wound after skin closure.” The wound after skin
`closure. The wound, as a standard, is closed in layers. We now
`prefer to excise the wound edges prior to closure to prevent
`hypertrophic scar formation.
`
`Results
`Two case examples are illustrated here to show the degree
`of correction that can be achieved with the MIS technique.
`In our first case, the patient is a 14 year-old girl with a 52°
`
`Figure 9 “Patient 1 - Anteroposterior and lateral preoperative radiographs.” Patient 1 - Anteroposterior and lateral radiographs show a 52°
`main thoracic curve and a 38° upper thoracic curve, with 24° dorsolumbar kyphosis. MIS technique was utilized (Figure 10 & 11), and both of
`the curves were instrumented.
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`Figure 10 “Patient 1 - 2-year postoperative anteroposterior
`and lateral radiographs.” 2-year postoperative correction
`anteroposterior and lateral X-rays of the patient in Figure 9. A 3-3-3
`pattern of instrumentation was utilized. The patient shows good
`correction, is well balanced in the coronal plane, the shoulders are
`level, and the dorsolumbar kyphosis has been restored to normal.
`
`had a Lenke type 5 curve. The cohort (6 female; 1 male)
`had a mean preoperative Cobb angle of 47.7° (range: 40°
`- 54°) and a mean preoperative kyphosis angle of 20.4°
`(range: 11° - 28°). The mean length of surgery was 8.71
`± (range: 7.25 - 9.66 hours), and average estimated
`blood loss was 564.3 (range: 100 - 1000 cc). Postopera-
`tive radiographic evaluation revealed a mean 8.66°
`(range: 4° - 11°) curve postoperatively, translating to an
`81.67% (range:75.8% - 92.6%) curve correction, with
`good maintenance of correction over the course of fol-
`low-up. CT based evaluation showed complete facet
`joint arthrodeses and revealed that 90.70% of pedicle
`screws were accurately placed within the cortical walls.
`A 2-year follow-up study by our group indicates that
`this minimally invasive technique provides similar defor-
`mity correction as a standard open posterior spinal
`fusion [13].
`
`Discussion
`Currently, we have limited use of this technique to
`curves which are less than 70° and reasonably flexible in
`
`Figure 11 “Patient 1 - 2-year postoperative anteroposterior
`and lateral radiographs.” 2-year postoperative correction
`anteroposterior and lateral X-rays of the patient in Figure 9. A 3-3-3
`pattern of instrumentation was utilized. The patient shows good
`correction, is well balanced in the coronal plane, the shoulders are
`level, and the dorsolumbar kyphosis has been restored to normal.
`
`order to limit the difficulty of these initial cases. For less
`flexible curves, we have utilized a transforaminal
`approach to a Smith-Peterson type osteotomy. This
`transforaminal osteotomy allows excision of the entire
`facet, facet joint capsule, and ligamentum flavum, while
`preserving the midline ligamentous and bony structures
`(Figure 16).
`Our initial results indicate that comparable correction
`can be achieved to the standard pedicle screw technique
`both in the coronal and sagittal planes. In flexible
`curves, correction of 75-80% can be achieved. In addi-
`tion, multiple other advantages to a minimally invasive
`technique include: less blood loss, shorter hospital stay,
`earlier mobilization, as well as less pain and need for
`pain medication [3,14]. However, further investigation is
`needed before similar claims can be made for this tech-
`nique. The operative time needed to complete this sur-
`gery is longer. However, this is expected in the learning
`of a new technique. We have found that the scar in
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`Figure 12 “Patient 1 - postoperative axial CT-Scan.“ The postoperative CT-scan of the patient shows adequate placement of the pedicle
`screws (6-0 × 40 mm screws were commonly utilized). Also notice that the lowest instrumented vertebra (L2) has been restored to nearly
`neutral rotation.
`
`Figure 13 “Patient 2 - Anteroposterior and lateral preoperative radiographs.” Anteroposterior and lateral radiographs show a 57° main
`thoracic curve which was corrected using the MIS technique. A slightly different pattern of pedicle screws was utilized in this patient, as shown
`in Figure 14 & 15.
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`Figure 14 “Patient 2 - Postoperative anteroposterior and
`lateral radiographs.” Postoperative images of the patient in Figure
`13. A slightly different instrumentation pattern has been used (3-3-4
`levels have been instrumented per incision). A good correction in
`both planes has been obtained, the shoulders are nearly level and
`the patient is balanced in the coronal plane.
`
`Figure 15 “Patient 2 - Postoperative anteroposterior and
`lateral radiographs.” Postoperative images of the patient in Figure
`13. A slightly different instrumentation pattern has been used (3-3-4
`levels have been instrumented per incision). A good correction in
`both planes has been obtained, the shoulders are nearly level and
`the patient is balanced in the coronal plane.
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`significantly outweigh its risks. Ketorolac effectively con-
`trols pain in pediatric surgery, and does not share the
`adverse effects of opioids, which include nausea and
`vomiting, respiratory depression, constipation, drowsi-
`ness, and potential for abuse [16]. Furthermore, patients
`treated with ketorolac have less postoperative pain result-
`ing in a shorter hospital stay, leading to lower hospital
`costs overall [17]. One retrospective study examining the
`effect of NSAIDs in adult spinal fusion patients demon-
`strated that ketorolac has a significant inhibitory effect
`on spinal fusion [18]. However, more recent studies on
`the adolescent population indicate that ketorolac does
`not influence the development of pseudoarthrosis after
`posterior spinal fusion in adolescent idiopathic scoliosis
`and does not increase risk of reoperation in children who
`underwent spinal surgery [16,17]. The clinical evidence
`that ketorolac is superior to morphine in terms of side
`effects and cost suggest that it be the analgesic of choice
`for minimally invasive scoliosis surgery.
`
`Conclusions
`We feel that a minimally invasive approach, although
`technically challenging, is a feasible option in patients
`with adolescent idiopathic scoliosis. Although there are
`multiple perceived benefits, long term data is needed
`before it can be recommended for routine use.
`
`Authors’ contributions
`VS was responsible for designing the instrumentation technique, data
`review, and draft and review of the manuscript.
`AW was responsible for designing the instrumentation technique and
`manuscript review.
`ES was responsible for data collection and review, manuscript drafting, and
`manuscript review.
`JH was responsible for manuscript revision, and data collection.
`MG was responsible for data collection and review.
`TA was responsible for designing the instrumentation technique, and
`manuscript review.
`All authors read and approved the final manuscript.
`
`Competing interests
`The authors declare the following competing interests:
`AW: Consultant/Speaker - Depuy Spine, Inc.
`VS: Consultant/Speaker - Depuy Spine, Inc.
`Consultant - Medtronic, Inc.
`AW, VS, TA: Research Grant - Stryker Corp.
`
`Received: 22 September 2010 Accepted: 11 August 2011
`Published: 11 August 2011
`
`2.
`
`References
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`3.
`
`Figure 16 “A trans-foraminal modified approach to a Ponte
`type osteotomy.” A trans-foraminal modified approach to a Ponte
`type osteotomy. We use this trans-foraminal osteotomy (TFO) for
`larger and less flexible curves. This approach allows for resection of
`the entire facet joint and ligamentum flavum. In the figure, notice a
`wide bone resection has been carried out while preserving the
`midline osteo-ligamentous complex. The tip of the suction is resting
`on the dura. In idiopathic cases, the ligamentum flavum can be left
`behind after resection of the facet joint.
`
`some patients may be, paradoxically, broader. This may
`be due to constant retraction of the wound edges. We
`now excise the wound edges prior to closure, with
`improved results postoperatively.
`The dosage and long term effects of using BMP in
`patients of childbearing age have not yet been fully
`established. Mulconrey and Lenke et al. ("Safety and effi-
`cacy of bone morphogenetic protein [rhBMP-2] in a
`complex pediatric spinal deformity at a minimum 2-year
`follow-up.” Presented at International Meeting on
`Advanced Spine Techniques, July 8-11, 2008, Hong
`Kong) assessed the safety and efficacy of BMP in 20
`patients treated for complex pediatric spine deformity
`with a minimum 2-year follow-up. One incidence of
`infection was reported, but there were no other compli-
`cations. Additionally, they found a 94% fusion rate over
`118 levels using 5.9 mg/level of BMP-2 (INFUSE - Med-
`tronic Sofamor Danek, Memphis, TN). In a recent
`review of the literature, Betz et al. concluded that BMP
`may be promising for enhancing fusion or as a bone
`graft substitute [15]. We have elected to use one large
`kit of BMP (12 mg total dose of INFUSE (1.5 mg/cc) -
`Medtronic Sofamor Danek, Memphis, TN) in these
`patients in order to ensure adequate fusion takes place.
`The long-term non-union rates in our patient popula-
`tion are not yet known, however, the short-term data is
`promising.
`The efficacy of ketorolac in postoperative pain manage-
`ment in pediatric surgical populations has been assessed,
`and its benefits in adolescent spinal fusion surgery
`
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`17.
`
`doi:10.1186/1748-7161-6-16
`Cite this article as: Sarwahi et al.: Minimally invasive scoliosis surgery:
`an innovative technique in patients with adolescent idiopathic scoliosis.
`Scoliosis 2011 6:16.
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