January 2, 2001
This was initially presented as a poster exhibit at the September 2000 Scoliosis Research Society annual meeting held in Cairns, Australia. Some of the statistics have been updated and will continue to be updated as time permits.
At this time we have performed the minimally invasive procedure on over 60 patients at Children's Hospital. Curves have ranged from 80 degrees to 37 degrees and from ages 10 years to 19 years. In addition the senior author has been co-surgeon on cases in other parts of the USA and prior to moving to Children's Hospital has done three patients over the age of 21.
The indications for a successful fusion is a healthy active person over the age of 9 or 10 with a single thoracic curve. There is always a compensatory thoracolumbar curve and if this is a secondary curve then it will often "bend out" with correction of the thoracic curve.
We usually brace adolescents with curves between 20 and 40 degrees and operate on those over 40 degrees but occasionally drop the indications to 35-37 degrees depending on age and deformity.
Our first case was done in January 1997 and as we looked at our initial results the correction was excellent averaging 62 degrees which equaled or exceeded results reported for posterior hooks and rods.
But the results in surgery are measured by time and looking at results over a two year period can significantly change the results compared to 6 months or 12 months.
At 12 months after surgery we had correction of 60% and no broken rods and basically no failures other than 2 patients who had severe curves and in whom the upper screws pulled out early in the post-operative time. This was not a disaster but certainly a disappointment.
Before we had developed the endoscopic techniques we would go in front and take out the discs to "loosen" the spine and then go posterior putting in the rods and hooks. If, now, we are successful in the correction of the curve through the anterior approach only - then we have saved a step - and if not, then unfortunately we're back to the standard front and back approach.
Because all metal will break and/or hardware loosen with motion it is essential that a solid fusion happens. If one takes a paper clip and bends it back and forth ten times, it will break. If the 3/16th inch rod bends ever so slightly 800,000 times it too may break. A solid fusion or connection between the bones will eliminate motion and the tendency for the rod to break.
At 12 months after surgery we had no broken rods. But by the longer time of greater than 24 months of follow-up we had 7 broken rods and those patients required re-operation by a posterior fusion and definitely were regarded as failures.
Of the remaining 21 patients followed for greater than 2 years our results generally were excellent. In all scoliosis fusions whether done in front or in back, there is a drop-off in the correction with time; and our successful results mimicked those reports for posterior fusion. Initial correction was 62%; at one year 60% correction and at 2 years 58% correction.
The reason for the failures could be due to our reliance on a bone graft material commercially available which normally does a good job of stimulating the bone to produce a fusion. It may be that after placing it in between the discs it "washed" away- or perhaps in this instance it was just ineffective. Regardless, looking at the decreased fusion rates [even in open procedures the failure to fuse rate is 12% ] we have significantly changed this part of the procedure and now use a calcium sulfate/bone graft with inductive bone stimulating capacity as a thick gel that really stays in place. In addition bone chips are packed into the disc space so that as the curve is corrected the bone graft is compressed into the disc space. Preliminary observation of the fusion would indicate better fusion results. In addition, compared to the extent of the discectomy done two years ago compared to the present, we are doing a far better discectomy as a result of experience which should significantly help both in the amount of correction and the ability to fuse.
In summary: Of 60 or more patients operated on for idiopathic scoliosis 7 of 28 had a failure at 2 years - 25%. On the other hand 75% were successful and those who failed the anterior part all had successful posterior fusion re-operations.
There were no disasters associated with this procedure, though the risks of pneumonia, screw loosening, hardware coming apart - were isolated events that occurred and were disappointing but not calamitous.
There were many outstanding corrections and results and as time and our experience increase we are constantly changing the details of the procedure to make it more efficient and successful, while at the same time maintaining the basic premise of a technique using three or four small incisions to loosen the spine, fuse it and correct the scoliosis.
Ronald G Blackman MD