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Minimally invasive scoliosis surgery: an innovative technique in patients with adolescent idiopathic scoliosis
© Sarwahi et al; licensee BioMed Central Ltd. 2011
Received: 22 September 2010
Accepted: 11 August 2011
Published: 11 August 2011
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.
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 instrumented are longer (7-13), the deformity exists in three planes, and the vertebral rotation can be significant. Placement 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 (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 . 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 morphogenic protein can be utilized, but is an off-label indication 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 percutaneous 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 typically have the ability to utilize multiple reduction maneuvers, including rod translation, rod derotation, in situ bending, direct vertebral rotation, and spine translation [8, 9]. Only limited reduction maneuvers can be carried out with the present minimally invasive spine surgery instrumentation systems . These instrumentation systems fall short in their ability to reduce a contoured rod into the pedicle screw heads. This is especially true when attempting to restore normal thoracic 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 limits incision length as well as soft-tissue dissection while allowing for deformity correction.
Materials & methods
Since May, 2008, we have been utilizing minimally invasive 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.
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 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). Postoperative 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 follow-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 deformity correction as a standard open posterior spinal fusion .
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 addition, 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 technique. The operative time needed to complete this surgery is longer. However, this is expected in the learning of a new technique. We have found that the scar in 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 efficacy 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 complications. Additionally, they found a 94% fusion rate over 118 levels using 5.9 mg/level of BMP-2 (INFUSE - Medtronic 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 . 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 population are not yet known, however, the short-term data is promising.
The efficacy of ketorolac in postoperative pain management in pediatric surgical populations has been assessed, and its benefits in adolescent spinal fusion surgery significantly outweigh its risks. Ketorolac effectively controls pain in pediatric surgery, and does not share the adverse effects of opioids, which include nausea and vomiting, respiratory depression, constipation, drowsiness, and potential for abuse . Furthermore, patients treated with ketorolac have less postoperative pain resulting in a shorter hospital stay, leading to lower hospital costs overall . One retrospective study examining the effect of NSAIDs in adult spinal fusion patients demonstrated that ketorolac has a significant inhibitory effect on spinal fusion . 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.
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.
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