Microsurgery in the lumbar intertransverse interval.

Abstract

The intertransverse interval has long been known as a place to lay bone graft in hope of achieving a solid arthrodesis. Opening it to use the interval to gain access into the foraminal and extraforaminal regions of the spinal canal has only recently been done. The anatomy is simple and embodies a common lumbar spine principle, which is to find a pedicle, because medial to it will be a nerve root. In the intertransverse interval, the lateral border of the pars interarticularis is on the same sagittal plane as the medial border of the pedicle (except for L5). Once through the interlaminar window, the anatomy is very simple--there is only one nerve root to find. The limited ability to manipulate instruments and the increased depth of the exposure make the use of the operating microscope very important. More so than axial MRI cuts and far more so than axial CT cuts, parasagittal MRI cuts reveal a true picture of the openness of the foramen. The type of pathology, whether E/FLDH or foraminal stenosis, can be clearly delineated on parasagittal MRI. It is important, however, that radiologists not overcall foraminal stenosis on axial cuts, either CT or MRI. Foraminal stenosis is easily decompressed by a lateral approach and is very difficult to completely decompress from within the spinal canal. If foraminal stenosis has been left behind from a previous midline SCS decompression, and if the patient has continuing leg pain, then it is easy to avoid the previous midline surgical route and take a paraspinal muscle-splitting approach to complete the foraminal decompression. Other, as yet undiscovered uses for the intertransverse window approach likely exist. The senior author has used this approach to remove a third- or fourth-time recurrent canalicular disk herniation where the fragment is opposite the disk space (the usual situation). By avoiding the previous scarred-in canal and nerve root, it has been possible to remove the ruptured disk. Visualization, however, is not good with this approach.