CHAPTER 58 Minimally Invasive Posterior Lumbar Fusion Techniques
Despite these advances, the morbidity of spinal fusion surgery remains significant. The standard posterior midline exposure is notorious for paraspinal muscle stripping and denervation leading to significant postoperative scar formation. The limitations of this approach for spinal fusion have been well documented, especially regarding a prolonged recovery period and muscle damage that may affect a patient following surgery.1–5
In recent years, less invasive surgical approaches have been developed to minimize damage to the paraspinal soft tissues during surgical exposure. These “minimally invasive” surgical approaches are becoming more popular because they offer the surgeon a method to achieve the goals of spinal surgery while minimizing some of the perioperative morbidity inherent to the classic posterior approach.6,7
Posterior Interbody and Transforaminal Interbody Fusion
When performing a posterior or transforaminal lumbar interbody fusion (PLIF and TLIF) via a minimally invasive approach, it is important to align the tubular retractor collinear with the disc space on the lateral view (Fig. 58–5). When performing a TLIF procedure, the tubular retractor must be aligned with enough lateral to medial angulation to allow the surgeon to reach the contralateral side of the disc space for preparation of an adequate fusion bed (Fig. 58–6). During the exposure, adequate facet joint must be removed to minimize retraction of the neural elements and provide working access to the disc space.8
The detrimental effects of over-retraction of the neural elements with the PLIF procedure have been well documented in the literature.9 Facet removals for a PLIF or TLIF can be achieved with either osteotomes or a high-speed burr. It is helpful to skeletonize the upper and medial portions of the caudal pedicle (e.g., L5 pedicle for a L4-5 TLIF) to gain adequate access to the disc space and allow safe retraction/protection of the dural/neural elements.
After disc space preparation, the interspace should be packed with autogenous bone graft or an adequate fusion substrate. An interbody fusion cage, of appropriate size, is selected and packed with the graft material, before impacting the cage into the disc space. The optimal position of the cage is toward the anterior portion of the disc space.10,11 This produces better reconstruction of the sagittal contour of the spine and allows ample bone graft material to be packed around and behind the cage.
Posterolateral Fusion (Intertransverse Onlay Fusion)
From the traditional midline approach, access to the intertransverse region for onlay fusion requires complete stripping of the paraspinal muscles to the tips of the transverse processes, an act that causes destruction, or at least disruption, of the multifidus muscle and significant postoperative scarring.5 Using the paraspinal muscle-splitting approach (Wiltse approach), exposure of the intertransverse region is simple to achieve without major muscle stripping. This provides direct access to the intertransverse region for fusion.

FIGURE 58–7 The use of an expandable tubular retractor allows simultaneous exposure of both transverse processes.
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