TLIF: Distraction, Annulotomy, Endplate Preparation, and Interbody Template Use
Part Four of Five
The most efficient means of creating distraction across the disc space is to use a laminal spreader on the contralateral hemilamina, which remains intact during the procedure. This will give the greatest amount of distraction with the least amount of risk. However, in cases where it is necessary to perform a bilateral laminectomy, the surgeon is unable to use the inter-lamina or transverse-laminal spreader. In these instances, the preferred mode of distraction is through the disc space itself by performing an initial discectomy and annulotomy, remove and evacuate as much disc space as possible, and then place within the disc space through the foraminotomy and fasciectomy site the interbody spreader or various twist spreaders that have been used to sequentially distract disc spaces while performing more traditional Posterior Lumbar Interbody Fusion (PLIF) techniques and bilateral posterior interbody fusion techniques. Once the disc space is distracted, the pedicle screws are placed prior to manipulating the disc space. The pedicle screws can then be locked in on the contralateral side with the appropriate size rod. Distraction is maintained while the remainder of the discectomy is performed.
Least Advantageous Distraction
The least advantageous means of distraction across the disc space is to place pedicle screws, distract across the pedicle screws, and then maintain the distraction by fixing the rod in this position. The direct distraction on the pedicle screws certainly creates risk of pedicle fracture especially in osteoporotic bone or loosening of the pedicle screw fixation, which the surgeon will need to rely on at the completion of the procedure.
Annulotomy and Endplate Preparation
After the posterolateral disc space is exposed and distraction is adequate to enter the disc space, a complete annulotomy is performed, and the initial aspect of the disc removal is started. A box cutter is needed to open up the entrance to the disc space. In many cases, posterior osteophytes narrow the entrance and the surgeon must be careful to remove the osteophytes to obtain a clean parallel exposure of the endplates and to avoid typical concavity of the endplates.
Endplate preparation is extremely important in any interbody fusion. A complete disc resection is necessary to maximize the fusion surface area. The annularis and annulus is maintained intact, but the periphery of the disc is removed up to the annulus to provide as much distraction and release as possible. The structural integrity of the endplates must be preserved to allow for structural support of the grafts. Once a complete discectomy and curettage of the endplate is performed, copious irrigation is used. The anterior aspect of the disc space can be further curettaged and, in some cases decorticated to provide an anterior fusion, which would give the surgeon the best chance of seeing a sentinel fusion develop across the disc space.
If a box cutter or chisel is used to square off the posterior osteophytes, great care should be taken. This offers one of the greatest moments of risk to the medial dural elements, as well as the exiting and traversing nerve roots. This is a vital step in preparation of the parallel endplates to avoid a loose-fitting graft within the concavity of the central disc space and an appropriate sizing. Removal of the posterior osteophytes will allow the surgeon to size the graft and size the parallel endplates as close as possible to an appropriate fit.
The final endplate preparation is performed using a rasp and various curettes to smooth and make parallel the entire disc space. Once the disc space is prepared and maximally distracted, interbody spacer templates are used to determine the appropriate width of the graft necessary.
Interbody Template Use
It is important to use interbody templates to ensure appropriate sizing of the graft. Templating should be performed in such a way as to provide a line-to-line fit; not one that appears too tight. It is important to remember that in the distracted position, once the interbody grafts are placed, the surgeon will then compress posterior instrumentation and load the devices anteriorly, thereby producing lordosis in the construct and further compression across the anterior grafts.