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Posterolateral Thoracolumbar Fusion


Summary of Key Points

  • The technique of posterolateral fusion is an essential part of a surgeon’s armamentarium.

  • Meticulous preparation of the fusion bed and placement of bone graft are important intraoperative steps for a successful fusion.

  • Pseudoarthrosis is a significant concern with noninstrumented fusions, occurring in 14% to 55% of these procedures. Pseudoarthrosis appears to occur less frequently with instrumented fusions (0%–18%).

  • Degenerative spondylolisthesis is one of the most studied indications for posterolateral fusion, and the role of fusion surgery continues to be evaluated in clinical trials.

  • Further studies are needed to better evaluate the cost effectiveness of noninstrumented fusions compared with instrumented fusions.

The technique of posterolateral lumbar fusion is an essential part of a surgeon’s armamentarium. In this chapter we review the surgical technique, the potential benefits and risks to this procedure, and the literature regarding indications, outcomes, and cost effectiveness.

Surgical Technique

The bony surfaces are exposed using a subperiosteal dissection. Levels are confirmed, and the lateral elements are identified. A posterolateral fusion includes the lateral facets, pars interarticularis, and transverse processes. If decompression is not needed, the medial structures—spinous processes, lamina, and medial facets—may be incorporated into the fusion mass and may bolster the posterolateral fusion.

Basic principles include creating a large surface area of cancellous bone (“bleeding bone”). Meticulous preparation of the fusion bed and direct contact of cancellous bone with graft material placed over the posterolateral vertebrae facilitates successful fusion ( Fig. 120.1 ). Care must also be taken to preserve the facet at the most superior level. The surgeon should also be aware of blood supply to the vertebrae to control intraoperative blood loss ( Fig. 120.2 ). Bone graft is packed into the bleeding fusion bed to create a scaffold over which bone may grow to fuse the articulations between the intended levels. The spinal canal and intervertebral foramina should be kept clear of bone graft.

Fig. 120.1, The joint surfaces are decorticated via high speed burr, rongeur, or osteotome. If a laminectomy is not performed, the posterior laminar surface can be decorticated to include in the fusion. The graft is packed over the decorticated areas.

Fig. 120.2, Lateral and posterior views of the arterial branches of the vertebrae.

Graft Materials

Osteoinduction, osteoconduction, and osteogenesis are needed for successful fusion to occur. The gold standard is iliac crest bone graft (ICBG), which was the foundation for successful posterolateral fusions in the 1920s and 1930s, and remains the standard to which other adjunctive therapies are compared. However, the harvest of ICBG is associated with complications such as surgical site infection, with a reported rate of 14.28% in a review by Calori et al., and donor site pain, with published rates ranging from 6% to 39% of cases.

Allograft and allograft-based materials are other grafting options that have osteoconductive properties. Some grafts, such as demineralized bone matrix (DBM), have a degree of osteoinduction owing to the bone morphogenetic proteins (BMPs) that they contain. A review by Buser et al. noted two comparable studies , of noninstrumented posterolateral fusion that compared allograft options, and found that the combination of DBM and lamina autograft had a fusion rate of 82.7%, compared with fresh frozen femoral head allograft, which had a fusion rate of 68%. DBM and autograft have not been compared head-to-head in the spine, and rates of fusion with DBM alone without additional autograft or allograft have not been assessed in noninstrumented fusion.

Synthetic scaffolding, which provides osteoconductive capabilities, has also been shown to be effective in fusions. When combined with recombinant human BMP-2, these scaffolds may outperform ICBG in terms of fusion rates. Boden et al. reported a fusion rate of 100% in 20 patients grafted with the scaffold/BMP combination—nine of which were noninstrumented fusions. In comparison, the instrumented fusion group with allograft only had a 40% fusion rate (two out of five patients with successful fusion, P ≤ .01).

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