Evidence & Methods
Surgical manipulation, scarring, and bone formation near the dorsal root ganglion have been concerns when considering the TLIF procedure. The off-label use of rhBMP-2 in TLIF has become increasingly popular, though the effects of this technique, compared with autograft use, are not well studied.
In this retrospective case series from one institution, the authors have found a relatively high complication rate using the TLIF technique, with specific complications associated with both rhBMP and autograft methods. Osteolysis and radiculitis rates in the rhBMP group (6% and 14%, respectively) are reported.
While TLIF technique is in some ways attractive, this study indicates adverse events are common. Operating through the foramen adjacent to sensory ganglion is associated with the risk of both direct intra-operative injury and the delayed radiculitis. The use of rhBMP in this area has additional unique problems, as noted in this study. The sobering complications reported in this study suggest the popularity of the TLIF, with or without rhBMP, may need reassessment and comparative studies evaluating competing strategies.
—The Editors
Prior studies have reported overall complication rates of up to 35% after the use of rhBMP-2 in the TLIF procedure [2], [3], [7], [10], [11]. These complications include pedicle screw malposition, interbody cage migration, hematoma, infection, CSF leak, transient and persistent nerve-related symptoms, heterotopic bone formation, and vertebral osteolysis.
Villavicencio et al. [7] reported a 12.7% (9/71 patients) incidence of postoperative neural injury after TLIF performed with rhBMP-2. Although most had resolution of their symptoms within 3 months, two of these patients had radiculopathy that persisted at most recent follow-up [7]. Potter et al. [2] in a retrospective study of 100 TLIF procedures performed with bone morphogenetic protein (BMP), reported a 7% incidence of postoperative transient radiculopathy. The most common nerve root affected was L5. Most cases resolved completely between 1 and 6 weeks postoperatively [2].
The use of rhBMP-2 for interbody fusion has raised concern for heterotopic bone formation in the epidural space. In a study by Paramore et al. [12], a canine model was used to investigate the effect of BMP that was intentionally placed into the subarachnoid space and fusion bed. At 16 weeks, new bone had developed in the subarachnoid space of all animals. Spinal cord compression and mild spinal stenosis were detected in all treated animals, but no clinical or pathological features of neurotoxicity were noted [12]. A recent study by Joseph and Rampersaud [13] assessed the incidence and clinical sequelae of heterotopic bone formation with the use of rhBMP-2 for posterior lumbar interbody fusion (PLIF) and TLIF. Heterotopic bone formation occurred in 20.8% with the use of BMP compared with 8.3% without the use of BMP. Despite the higher incidence, there does not seem to be any associated clinical sequelae [13]. Several past studies have demonstrated similar findings [3], [12], [13], [14], [15].
The reported rate of vertebral end plate resorption and osteolysis after TLIF using rhBMP-2 varies widely. This variability is likely because of differences in surgical technique, diagnostic imaging, and the definition of vertebral osteolysis used to make the diagnosis. A 2006 study by McClellan et al. [16] demonstrated vertebral bone resorption at 22 lumbar levels of the 32 reviewed by computed tomography (CT) scan (68.8%). The defects were characterized as severe in 31% (7 of 22), which were often associated with graft subsidence and loss of end plate integrity (5/7, 74%) [16]. Lewandrowski et al. [10] reported a 7.4% incidence (5 of 68) after single-level TLIF using cages and rhBMP-2. Each patient reported worsening back pain with variable radicular pain as early as 4 weeks and as late as 3 months from his or her date of surgery. The defects filled in spontaneously, and symptoms typically resolved within an additional 3 months of nonoperative care [10]. A study by Vaidya et al. [17] evaluating the complications with the use of rhBMP-2 in polyetheretherketone (PEEK) cages for interbody fusions noted an 82% (41/50) rate of lumbar end plate resorption. In this study, the diagnosis and extent of resorption was based on plain radiographic findings and even minor indistinctness of end plates was considered a positive finding [17]. Most studies report that vertebral osteolysis is a self-liming phenomenon that does not affect fusion rate or clinical outcome.
Most existing studies on the TLIF procedure are limited in that they contain small and/or heterogeneous groups of patients. It is important to study the complications of such a procedure that is increasingly using rhBMP-2 in an “off-label” fashion. The purpose of this study was to document the complications that occur after a single-level TLIF procedure performed at a single institution. A comparison of the rate and type of complications that occur with the use of iliac crest autograft versus rhBMP-2 will be made. We hypothesize that the two study groups will have similar complication rates.
