After removing the final dilator, very little muscle tissue should be seen within the confines of the retractor blades. Expansion of the retractor blades in modular systems should be limited to prevent muscle creep. Over-expansion of the retractor blades should be avoided as it does not improve exposure and causes more muscle creep. We use limited monopolar electrocautery to clear residual muscle, being careful not to create excessive tissue necrosis. Once the facet joint is encountered, this is marked for level confirmation on lateral fluoroscopy. Once the retractor is in good position and at the correct level avoid the temptation of moving the retractor frequently as this leads to muscle creep.

Now that the facet joint is exposed, osteophytes are resected and the joint line is identified (Fig. 15.3). It is important to use the facet joint for orientation. This is a standard anatomical guide for the remainder of the surgical procedure including the decompression, TLIF, and pedicle screw placement. There is no need to expose the transverse process as this leads to unnecessary surgery trauma of the soft tissues and more bleeding.

The facetectomy side for the TLIF is chosen on the more symptomatic side. If the symptoms are bilateral, then the side of more advanced anatomical stenosis is chosen. The pars inter-articularis and lamina are identified and cleared of all soft tissue. At this point a half-inch osteotome or high-speed burr is used to complete the osteotomy of the descending articular process. The resection of the descending articular process should be such that the underlying ascending articular process should be exposed enough to visualize its medial and superior border (Fig. 15.4). The ascending articular process is then resected to expose the working TLIF portal between the exiting and traversing nerve roots. Significant epidural bleeding can be encountered while removing the ascending articular process. This can be controlled using bipolar cautery and/or collagen/thrombin paste product. The ligamentum flavum is not removed at this time and is left intact during the TLIF, as it provides protection to the underlying dura and traversing nerve root while the interbody work is being performed (Fig. 15.5). The exiting nerve root normally lies in the upper half of the foramen even in low-grade spondylolisthesis. This exiting nerve root need not be visualized and the overlying cranial pars inter-articularis is preserved to protect this nerve during interbody work.

A standard inter-laminar spreader or distractor cannot be used in this MIS approach as is commonly performed in the open technique. Hence, slight kyphotic positioning on a Wilson frame allows for entry into the disc space and protection of the exiting nerve root. A 15-number surgical blade is used to make a 1 cm² annulotomy in the TLIF access portal. A subtotal discectomy is done in the usually fashion using a combination of curettes and paddle shavers. Adequate time should be spent preparing the disc space since this is critical in obtaining a solid interbody fusion.

In certain cases, the disc space is severely collapsed making entry into the disc space difficult. In these cases a quarter inch osteotome can be used to gain entry into the disc space followed by serial dilation. The space can be further distracted using rotating paddle shavers. Another option is to distract on the pedicle screw instrumentation on the contralateral side of the TLIF to attempt to restore disc space height while performing the TLIF.

Reduction of the spondylolisthesis is accomplished in several ways. The first is postural. Oftentimes when placing the patient in the prone position under general anesthesia with muscle relaxation partial reduction the spondylolisthesis occurs. In addition, disc height restoration most often improves the slip magnitude, as well as the slip angle. Finally, reduction instrumentation can be employed. If instrumented reduction is planned, this is done prior to placement of the interbody cage device and interbody bone grafting.

Several types of structural interbody supports are commonly used based on the surgeon’s preference. Shape configurations commonly include bulleted and kidney-bean shape made of PEEK, titanium, or allograft. There are many bone graft options available. Products of decompression (local autograft) are an excellent source of bone if properly cleaned of all soft tissue. This bone is morselized and placed into the disc space and potentially the cage device. Bone graft extenders can be used in addition to the local bone.

Once the interbody work is completed, formal decompression is carried out as required on a case-by-case basis. This is done after the TLIF so that the lamina and the ligamentum flavum protect the dura and traversing nerve root from iatrogenic injury during the interbody preparation. In many cases the dura expands laterally after removal of the ligamentum flavum into the TLIF working zone. Once the ipsilateral decompression is completed the contralateral side is addressed as needed.

When contralateral decompression is required this is routinely preformed from the TLIF side. The retractor is gently redirected to the junction of the lamina and spinous process. The remaining ipsilateral lamina and the base of the spinous process are resected. The interspinous ligament is kept intact. The contralateral ligamentum flavum is now well visualized. To initiate the “over-the-top” decompression, a plane is created between the ligamentum flavum and dura. The dura and neural elements are protected and gently retracted with cottonoids as required. This is followed by using straight Kerrison ronguers for resection of any lateral recess stenosis caused by the arthritic facet joint to decompress the traversing nerve root. A formal foraminotomy can be preformed to decompress the exiting nerve root as well. Hemostasis is critical during this focused decompression and is best accomplished with judicial use of bipolar electrocautery and collagen/thrombin hemostasis products. The completed contralateral decompression is confirmed using direct visualization and a ball-tip probe (Fig. 15.6).

At this point pedicle screws are placed on the side of the TLIF and decompression (Fig. 15.7). When using a tubular retractor system, direct visualization of the anatomy for screw placement is possible. Lateral expose to the transverse processes is not generally required. The mammillary process, facet joint anatomy, and the lateral pars inter-articularis provide enough information to identify the pedicle screw starting point. Good three-dimensional orientation is a must for safe pedicle screw insertion with this technique. A standard pedicle probe is used to cannulate each of the pedicles. All pedicle sites are cannulated prior to screw placement. This allows for maximal visualization of the anatomy prior to introduction of the pedicle screws. There is no need for the use of K-wires or cannulated pedicle screws with this direct insertion technique. Lateral fluoroscopy is occasionally used during placement; however, judicial use is important. An AP is typically obtained only after all screws are placed.