Minimally Invasive Surgery for Adolescent Idiopathic Scoliosis Shows Same Efficacy as Open Approach with Less Transfusion Needs

Peer Commentary by Baron S. Lonner, MD and Author's Response by Vishal Sarwahi, MD

Use of minimally invasive surgery (MIS) for management of adolescent idiopathic scoliosis (AIS) resulted in similar rates of deformity correction and adequate fusion compared with standard open posterior spinal fusion (PSF), but with some shortcomings related to learning curve and instrumentation, according to a retrospective controlled study in the October issue of Clinical Spine Surgery. The study is the first published case series of the MIS approach to treating AIS, the investigators noted.

minimally invasive surgical technique for adolescent idiopathic scoliosis

“Standard open AIS surgery is highly successful. To replicate that efficacy with the advantage of needing less blood transfusion and less disruption to the normal anatomy is a major milestone,” said lead author Vishal Sarwahi, MD, Associate Surgeon-in-Chief and Chief of Spinal Deformity and Pediatric Orthopaedics at Cohen’s Children Medical Center, in New Hyde Park, NY, and at Northwell Hofstra School of Medicine, in Hempstead, NY.

Retrospective Controlled Study
The investigators compared follow-up data from 7 patients with AIS who underwent MIS and 15 patients who underwent PSF. The two groups were similar in terms of age, sex, height, weight, levels instrumented, and preoperative curve. All patients were followed for a minimum of 2 years postoperatively.

Radiographic outcomes showed a median curve correction of 79.25% and 84.78% in the MIS and PSF groups, respectively (P=0.503). Screw placement accuracy also was similar between the two groups with rates 90.7% and 90.8% in the respective groups. In addition, all 5 of the 7 patients in the MIS group who underwent CT scans postoperatively showed solid fusion at the facet joint as well as at the intervening uninstrumented level.  

Minimally Invasive Approach Negated Need for Intraoperative Blood Transfusion
Estimated blood loss was lower in the MIS group than in the PSF (600 vs 800 mL), but the difference was not statistically significant (P=0.051). Intraoperative blood transfusion was used in 7 patients (47%) in the PSF group compared with none of the patients in the MIS group (P=0.02).

The MIS group showed a longer median operative time (P=0.011) despite having fewer fixation points (P=0.015). Postoperative recovery was similar between the groups, including the number of ICU days, length of hospital stay, time to mobilization, pain scores, and use of patient-controlled analgesia.

The complications occurred more frequently in the MIS group than in the PSF group (71.4% vs 33.3%), but the overall complication rate was not significantly different (P=0.56). Major complications in the MIS group included one case each of rod dislodgment, wound infection, and implant prominence causing wound dehiscence.

Improved Instrumentation and Implant Design for MIS Approach Needed
Dr. Sarwahi said that increased surgical experience and modification of instrumentation and implants may improve the complication rate with MIS in the management of AIS. Currently, surgeons are using implants and instruments in MIS that are meant for open standard surgery, “which is less than ideal,” Dr. Sarwahi told SpineUniverse.

“Evolution of the technique and modification of the implant and instrument design will decrease the complication rate substantially,” Dr. Sarwahi added. “It is our experience and that of others utilizing MIS technique that the learning curve for this approach is approximately 20 to 25 cases, he noted.

MIS Approach May Benefit Patients With Neuromuscular Scoliosis
Dr. Sarwahi and colleagues have begun using the MIS approach to treat more severe forms of scoliosis, including neuromuscular and syndromic scoliosis, and found that patients are discharged within 4 to 5 days of MIS as opposed to 2 to 3 weeks following standard open surgery. In addition, the MIS approach requires markedly fewer units of blood transfused in these patients, typically only 1 unit of blood, shorter ICU stay and lesser amount of pain medication according to Dr. Sarwahi.

postoperative clinical image of child treated using MIS for AIS


Baron S. Lonner, MD
Chief of the Division of Spine Surgery
Professor of Orthopaedic Surgery
Mount Sinai Hospital
New York, NY

Sarwahi et al are to be commended for critically assessing their patient outcomes in MIS surgery for AIS compared to the standard open posterior approach. The authors have found similar curve corrections for both MIS and open procedures in this small series of patients with moderate curves. Similar postoperative pain scores and hospital length of stay were noted between groups, and operative time was nearly two hours longer for the MIS procedure. Blood loss was slightly less for the MIS procedure.

Given these findings, one must question what advantage the MIS approach has in the AIS population in which outcomes have been historically excellent with relatively low complication rates and low operative morbidity. In fact, a relatively high revision surgical rate was reported, with 3 out of 7 patients requiring additional surgery because of infection, implant problems, and a third condition that was not clearly stated in the study. The benefits of MIS surgery in this patient group are unclear as opposed to the potential benefits that may be seen in the adult population in which greater blood loss, higher infection rates, and junctional deformities have been a problem with standard open posterior approaches. Thoracoscopic anterior instrumentation procedures in vogue 10-15 years ago held a lot of promise and were associated with shorter fusions than open posterior surgery, but came at the cost of higher revision rates for implant breakage, pseudarthrosis, and loss of correction.

A number of questions and concerns arise in relation to the performance of posterior MIS procedures for AIS:

  • Firstly, what is the learning curve for the surgeon? How many cases are required before the surgeon becomes proficient and what complications arise as one progresses through the learning curve?
  • Can these techniques be readily applied to larger and more rigid curves and will correction of spinal deformity for these more severe deformities be equivalent to those performed in an open fashion?
  • Are the costs associated with MIS implants much more substantial than with the standard implants and if so, how can one justify the use of these implants in this day of cost and value quality metrics?
  • How can one justify the use of BMP-2 in the pediatric population with its increased cost and unknown risk in the skeletally immature population, again when open surgery results in reproducible outcomes with equivalent recovery time?
  • Will fusion occur as reliably in patients treated with MIS compared to open posterior surgery? Only 5/7 patients had postoperative CT scans demonstrating solid fusion. Much larger series are required in order to be adequately powered to determine whether or not this is reliably achieved with MIS procedures. 

This initial report shows little benefit of MIS surgery over standard technique except for a smaller overall incision length divided into three incisions.

The authors involved in this study have done an excellent job of collecting data and studying their patients. If they continue to utilize the MIS approach, they should follow larger cohorts out to a minimum of two years and report on their outcomes. No doubt, improvements in the instrumentation and techniques will occur, possibly resulting in more efficient operations with shorter lengths of stay and lower complication rates than what is being reported currently.

Author’s Response

Vishal Sarwahi, MD
Associate Surgeon-in-Chief
Chief of Spine Deformity Surgery and Pediatric Orthopaedics
Steven and Alexandra Cohen's Medical Center of New York
North Shore Long Island Jewish Health System
New Hyde Park, NY

We appreciate Dr. Lonner’s thoughtful insight. We could not agree more that minimally invasive scoliosis surgery in AIS patients is still evolving, and thus it is not surprising that surgery takes longer, and has a steep learning curve. We did not find immediate perioperative benefits of MIS that have been reported in adults. However, avoidance of blood transfusion and associated risks is a significant advantage all in itself, and its importance cannot be minimized in the adolescent population. The study reviewed patients operated 7-8 years ago and represents our earliest experience, and we continue to offer this to our patients. Our philosophy is to continue advancement in the pediatric deformity surgery, although as pointed out by Dr. Lonner, the standard operation is a very safe and successful procedure. The MIS approach is through pre-existing muscle planes, and is minimally disruptive allowing for soft tissue preservation. It achieves a similar degree of correction and comparable accuracy rate while saving levels. Additionally, in this adolescent population, cosmesis is a major concern. If similar deformity correction results can be achieved, while allowing for smaller scars, then this is something we would like to continue to develop.

In response to Dr. Lonner’s concerns:

  1. We estimate 25 MIS cases in AIS will allow a surgeon to be proficient.
  2. Complications in our original study were statistically comparable to the standard approach, and in our continuing experience, the complications have decreased. We have recently submitted our updated case experience documenting these results.
  3. We have previously recommended utilizing MIS in curves up to 70-degrees, however, we have continued to challenge the limits and have operated on 90-degree AIS curves. Larger and more rigid curves often need complete facetectomies, which has been previously described by us (Scoliosis. 2011; 6:16). This allows for similar curve correction.
  4. Cost is an important issue, and for our technique, we utilize standard implants and not MIS implants. Cost analysis, as part of our recent study, shows MIS to be less expensive than the standard because of fewer screws being utilized.
  5. At present, we do not use BMP-2 for MIS procedures. We utilize autograft and allograft and have not found a difference in fusion as confirmed on CT scan and clinical follow-up. These results have been submitted for publication.

Our published study represents a very early experience with its own limitations. Over the last few years, outcomes of subsequent patients and data from spinal surgeons have corroborated our findings that MIS is a viable alternative to the standard approach. We continue to develop the procedure, and have a multi-institutional prospective study in place. As our experience grows, we have expanded the technique to larger curves and neuromuscular patients, and are convinced that the MIS approach will be the preferred approach in the future.

Updated on: 01/19/17
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