TLIF: Indications for Pseudoarthrosis
Part Three of Five
Other indications include patients who at high risk for pseudoarthrosis due to a previously failed fusion, osteoporosis, concurred medical illness, or smoking history. These patients are also at greater risk of nonunion for a simple posterolateral intertransverse process fusion.
In these situations, the addition of the interbody fusion would certainly increase the viability and success of the overall fusion construct. In patients who have osteopenic bone and risk kyphotic potential with a large disc space, load sharing is improved and stress is removed from the pedicle screws by placing an anterior column construct to support the anterior two-thirds of the vertebral body. The Transforaminal Lumbar Interbody Fusion (TLIF) procedure is also suitable in cases where an Anterior Lumbar Interbody Fusion (ALIF) is not possible either due to previous anterior surgery, significant medical illnesses, obesity, or in a young male who does not want to entertain the risk of retrograde ejaculation.
Principles to Emphasize
The principles to emphasize while performing this procedure include the anatomical fine points of the exposure and then the biomechanical manipulation of sagittal contours throughout the procedure to maximize both the exposure and eventual surgical success. A wide hemilaminectomy is necessary, especially in a revision case, but even in the primary surgery to expose the lateral aspect of the lamina and facet joint foramen of the exiting nerve root, as well as proper visualization of the traversing nerve root.
It is within the safe zone of the posterolateral disc that the surgeon will encounter appropriate room to complete the discectomy, insertion of various instruments, and structural grafts. A foraminotomy is associated with either a partial or complete fasiectomy depending on the anatomy with exposure from the superior pedicle to the inferior pedicle. Once this is accomplished, the exiting nerve root must be manipulated as little possible as this is the location of the dorsal root ganglion, which exits in this lateral position. This is an extremely sensitive portion of the nerve and is prone to significant injury, which can result in long-term dysesthesias and post-operative pain.
With significant disc collapse or spondylolisthesis, it may be difficult to gain adequate exposure to the disc space with a simple fasciectomy and foraminotomy. It is in this situation that distraction across the disc space will provide its best and it's most advantageous participation in exposure. With distraction across the disc space, the exiting nerve root superiorly will be moved in a cranial direction in association with its pedicle, thereby widening the distance between itself and the distal traversing nerve root giving a greater window of exposure to the posterolateral disc space. Distraction not only facilitates entrance into the disc space, but also allows for a greater evacuation of the disc space, better visualization of the endplates, and a greater structural distraction of the disc space in the final construct.
Certainly there are risks to distracting across the disc space and this must be done gently. This can be accomplished by numerous mechanisms. The more common techniques involve direct manipulation of the disc space, easing interbody spreaders; either self-retaining or with twist spreader, and spatulas used with other TLIF sets. The surgeon can also use a laminal spreader if one is maintained in the contralateral lamina of the interval in question, or the surgeon can distract via the pedicle screws over the motion segment in question.
Risks of Distraction
The risks of distraction involve an inadvertent injury to the dorsal root ganglion, fracture of the bony anatomy, and neural injury to the midline dura due to manipulation.