Overview

Posterior lumbar interbody fusion (PLIF) after lumbar disk removal was first reported by Jaslow in 1946, and Cloward presented his first 100 cases at the Harvey Cushing Society meeting in 1947. More recently, Steffe, Brantigan, and Ray have reported on the use of posterior segmental instrumentation or cage implants for PLIF, a surgical technique that allows fusion across two adjacent vertebrae by inserting grafts, titanium-threaded cages, bone dowels, or carbon-fiber spacers filled with bone graft into the disk space. All PLIF techniques require removal of the disk material from within the disk space; bone grafts and spacing devices are then used to create a bony “bridge” that will fuse the two adjacent vertebral bodies.

PLIF is a valuable way of achieving a spinal fusion. If spinal instability is present (i.e., spondylolisthesis or slippage of the vertebrae), PLIF should be performed with spinal stabilizing instruments, such as pedicle screws or hooks and rods to immobilize the loose vertebrae. The many advantages in instrumented PLIFs, or 360-degree fusions, include a decrease in pain and an increase in functional activities. Compared with anterior-posterior (AP) fusions, instrumented PLIFs also have equal patient satisfaction, much lower costs, and faster return to work and other activities. Furthermore, a recent biomechanical study by Bennett and associates found that PLIFs double the spinal stiffness produced by transpedicular fixation following laminectomy and facetectomy. Other theoretical advantages of PLIF are technical and include the fact that a much larger area of bone surface exists for the fusion, with the fusion at the center of motion and at the site of maximum compression loading. The disk space is maintained in a distracted position without the collapse that is often seen in transverse-process fusion using transpedicular fixation. In addition, the blood supply is better at the decorticated end plate than at the transverse process.

Perhaps the greatest concern with a standard PLIF is the amount of neural retraction needed. An inappropriate amount could potentially lead to nerve root injury, cauda equina injury, dural laceration, and epidural fibrosis. Consequently, the unilateral posterior transforaminal lumbar interbody fusion (TLIF) was developed to address some of these problems. The concept of a unilateral approach to the anterior column was refined and popularized by Harms. The purpose of this approach was to obtain the same goals as a PLIF without the potential risks and complications.

The TLIF technique allows clearance of the entire intervertebral disk compartment by opening the neural foramen on one side. After appropriate clearance, it is possible to achieve further enlargement of the cleared intervertebral compartment by posterior transpedicular distraction. This enables definitive anterior column support and certain fusion by transforaminally introduced bone material and support structures. After the introduction of these anterior fusional elements, segment stability is restored by converting the distraction force into compression force. The TLIF approach helps to avoid damage to important anatomic structures, such as the nerve roots, dura, ligamentum flavum, and interspinous ligament.

Preservation of the ligamentous structures is of great importance to restoring biomechanical stability of the segment and its adjacent counterparts. The advantages of unilateral TLIF over the standard PLIF include the ability to provide bilateral anterior column support through a single posterolateral approach of the disk space. The transforaminal approach preserves the anterior and most of the posterior longitudinal ligamentous (PLL) complex, which provides a tension band for compression of the graft and prevents retropulsion of the graft. It avoids excessive soft-tissue dissection, which may help prevent scarring, instability of adjacent segments, and injury to the exiting nerve root. Epidural bleeding is less of a problem than with the standard bilateral PLIF because of the unilateral transforaminal approach, and with experience, proper cage placement within the disk space is consistently achieved.

Indications and Contraindications

Operative Technique