Direct Lateral Approach to the Lumbar Spine

Extreme lateral interbody fusion (XLIF) (NuVasive Inc., San Diego, CA) and direct lateral interbody fusion (DLIF) (Medtronic Sofamor Danek, Memphis, TN) are novel minimally invasive transpsoas approaches to the lumbar spine for performing interbody fusions. Advantages of interbody fusions over posterolateral fusion have been detailed and include theoretically higher fusion rates, the possibility of achieving better sagittal alignment, and even possibly better outcomes. Anterior lumbar interbody fusion (ALIF) provides a theoretical advantage over posterior methods of interbody fusion by allowing a greater extent of discectomy, avoiding entry in to the spinal canal and subsequent scarring adjacent to the neural elements and sparing of the posterior elements of exposurerelated damage. Despite its advantages, the ALIF approach is also associated with several serious complications including visceral and ureteral injury, vascular injury, and sexual dysfunction among others. Various minimally invasive techniques have been developed to perform ALIF including laparoscopic and endoscopic techniques and the miniopen approach. These, however, require a steep learning curve and the potential for serious complications remain. In addition, an endoscopic minimally invasive transpsoas approach has also been described. This, however, is of historic value and represents a technique that eventually evolved into both the XLIF and the DLIF. For the purpose of this discussion, we will reference the XLIF approach. The discussion, however, does apply also to the DLIF. XLIF uses a minimally invasive, transpsoas approach to the spine (Fig. 19.1). The surgeon uses his or her fi nger to perform blunt dissection through a posterior paraspinal incision to escort dilators and a guide wire into position directly over the psoas muscle. Using his or her fi nger the surgeon is able to create a retroperitoneal space and protect the viscera and prevent possible injury. With the DLIF technique, some surgeons have chosen to perform this procedure through a single miniopen lateral approach without the use of the posterior incision to create the retroperitoneal space. With the single incision, the layers of the abdominal wall are directly visualized, and the retroperitoneal space is created under direct vision with passage of instruments through the psoas. In addition, the use of electrophysiological monitoring, including triggered and freerunning electromyography (EMG), reduces the likelihood of injury to the lumbosacral plexus when accessing the disc space through the psoas muscle. Dilators, which contain insulated tips allow for EMG monitoring as they are introduced via the transpsoas approach to the disc space. If a dilator passes in proximity to the lumbosacral plexus, the surgeon is warned both visibly on a graphic display and also via auditory feedback. The surgeon can then adjust his or her trajectory to reduce the likelihood of neural injury. Given the location of the lumbosacral plexus described by Moro et al, a more anterior trajectory is safer especially at the L4-5 interspace. Nevertheless, genitofemoral nerve injuries can still occur. Simply using fl uoroscopy and serial dilatation of the psoas muscle, the surgeon readily and safely can access the disc space. The major advantage of XLIF/DLIF is the fact that the procedure does not require a second access surgeon. Other advantages are reduced incidence of ileus, the anterior longitudinal and posterior longitudinal ligaments remain intact, the lack of need for bony resection as performed when posterior approaches for interbody fusion are being used, reduced operative time in comparison to other anterior approaches, and reduced postoperative hospital stay and analgesic requirements (Table 19.1). In deciding to use this approach over others, a fl owchart is included to assist the reader in decision making versus other techniques (Fig. 19.2).