Spinal Fusion

Modern Spine Fusion Techniques

By: John E. Sherman, MD
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post lateral fusion
Fig 1: Posterolateral gutter fusion surgery (view larger)

The two primary types of medical devices used in a spinal fusion surgery include pedicle screws and anterior interbody cages or spacers. When it has been determined that a spine fusion is appropriate, the surgical technique utilized may vary.

There are several types of spinal fusion, including:

  1. Posterior approaches to spine fusion
     The surgical techniques that have historically been used the most comprise spine fusion surgery that is approached posteriorly, or from the back (vs. anteriorly, or through the abdomen). There are three main posterior fusion techniques( all three are usually performed with pedicle screw fixation):
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      • Posterolateral gutter fusion surgery. This type of spinal fusion involves placing bone graft in the posterolateral portion of the spine (a region just outside the back of the spine). This type of fusion has a long history and has been the most commonly used approach (see Figure 1).
      • Posterior lumbar interbody fusion (PLIF) surgery. A PLIF involves placing bone graft and/or spinal implant (e.g. cage) directly into the disc space in the front of the spine.
      • Transforaminal lumbar interbody fusion (TLIF) surgery. A TLIF is essentially like an extended PLIF, as it also involves expanding the disc space by removing one entire facet joint (whereas a PLIF usually involves gaining access to the disc space by removing a portion of the facet joints on each side of the spine).

    1. Anterior approaches to spine fusion
       An anterior approach (from the front) to spine fusion allows the surgeon to place bone directly in the space between the vertebrae where the disc had been. Because approximately 80% of the forces of the spine are borne through the disc space, it is much more likely that a solid fusion will be achieved and patients will have pain relief if the fusion includes the disc space. There are two primary techniques to accomplish this.

      2. More Spinal Fusion Info:

      Lumbar Spinal Fusion

      Elements of Spinal Fusion

      Spinal Fusion Recovery

      Spinal Fusion History

      • Anterior/posterior lumbar fusion
        An anterior/posterior fusion surgery is typically performed through an incision in the abdomen, with removal of the disc and placement of bone graft where the disc material has been removed. A separate incision is made in the back to place the pedicle fixation and bone graft. This approach may include a large amount of trauma to the muscles, a long hospital stay, and may at times be associated with a fair amount of blood loss. However, in cases where there is a lot of instability, an anterior/posterior fusion surgery can be necessary as it provides the greatest amount of stability.
      • Anterior lumbar interbody fusion
        An anterior lumbar interbody fusion is a surgery technique that involves the placement of bone graft with a plate or secored spacer or bone graft with an anterior interbody cage within the disc space. The most efficient way to place this is through the abdomen into the disc space. Most commonly, persons who have undergone this spine fusion surgery are able to return to their activities more rapidly. This type of approach can be used in cases where there is not a lot of associated instability and the disc space is narrow. The results of stand alone anterior fusions are not as good for multilevel constructs.

    Additional factors for spinal fusion surgery:

    In addition to the approach used, there are a number of other factors to be considered before spine fusion surgery. The following discusses several other considerations.

    PLIF and TLIF surgery

    The PLIF and TLIF allow for placement of bone or a cage in the disc space, increasing the fusion rate and hopefully a better clinical outcome. There is more neurologic risk because of the need to retract the nerve roots, however, major nerve injury is unusual. It has the advantage of placing a structural graft or device in the major weight-bearing part of the spine while avoiding a separate incision.

    Bone graft

    Traditionally bone graft has been harvested from the patient’s own iliac crest (pelvis) to stimulate the fusion site. Cadaver bone often is useful in anterior fusions, but it works poorly in posterior applications. Recent advances have allowed spine surgeons to decrease the need for bone graft harvest by using substitutes, e.g., collagen sponges, demineralized bone matrix, platelet derived growth factors and, most promising, bone morphogenic protein (BMP). The bone morphogenic protein currently in use (Infuse) has FDA approval for anterior application only. Further research is ongoing to document the utility of these products, which allow for diminished patient trauma that can occur from harvesting bone graft from the patient's own hip.

    Minimally Invasive Surgery (MIS)

    Much work is in development to try to decrease the trauma patients incur by placing pedicle screws through smaller incisions. This is thought to result in less muscle trauma and allow for more rapid recovery after spine surgery. Caution needs to be exercised, however, as even though a technique is less traumatic, if the spine fusion rate is much lower, then there is really not an advantage. Also, it has yet to be demonstrated that minimally invasive spine fusion systems actually cause better outcomes than some other surgical techniques used in the traditional open approach.

    John E. Sherman, MD
    September 8, 2006
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