Lumbar Interbody Fusion

Interbody Fusion Approaches and Techniques

Interbody fusion can be performed via several surgical approaches including anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF) ( Fig. 24.2 ). The ideal setting for fusion to develop across the disk space is a clean bone surface across apposing endplates. Therefore regardless of the surgical approach, a total diskectomy is performed at the level of concern through a surgical window in the annulus fibrosus. An osseous substrate is then implanted into the disk space in between the decorticated bleeding surfaces of the adjacent endplates, which serves as a favorable environment for fusion by means of bone formation and healing. The insertion of bone graft material may be conducted with or without interbody spacers (to achieve ligamentotaxis). The implanted osseous substrates placed in the disk space are generally in the form of interbody spacers that are either solid or openwork structures usually filled with bone graft material. The spacer is meant to maintain alignment, provide spinal column support, and promote fusion. Fusion may be attempted at a single or multiple spinal segments.

In addition, supplemental segmental hardware instrumentation (posterior rods and pedicle screws, plates, and intervertebral implants) may accompany the interbody fusion ( Fig. 24.3 ). Instrumentation itself is not meant to fuse but to stabilize, so that osseous fusion may develop. The aim of the hardware is to immediately stabilize the spine, maintain alignment, limit postoperative segmental motion, and replace excised anatomic components. The hardware limits motion by acting as a rigid internal fixation device and thus provides the stability that favors osseous fusion. An understanding of this point is essential, since it is acknowledged that instrumentation without osseous fusion will be generally unsuccessful. In other words, hardware itself is insufficient for fusion.

Anterior Lumbar Interbody Fusion

If an interbody fusion is large enough, it can on its own provide sufficient motion limitation and biomechanical stability to promote fusion. ALIF provides optimal disk space access allowing for complete anterior and central disk removal, which in turn allows for an optimally sized device to be placed. Therefore ALIF is the only approach that does not require supplemental posterior hardware to ensure stability and motion limitation throughout the fusion process. ALIF utilizes single large cages typically supplemented by an anterior plate ( Fig. 24.4 ). The ALIF approach avoids damage to the motion limiting posterolateral vertebral elements, avoids damaging the posterior musculature, and decreases the risk of epidural fibrosis. If delayed arthrodesis is evident after stand-alone ALIF, a second posterior instrumentation procedure can be performed to further promote solid arthrodesis. Importantly, the approach requires skilled surgical expertise to avoid abdominal and vascular complications.