This session of the First Annual Lumbar Total Disc Replacement Summit focused on discussions regarding possible complications with lumbar surgery, considering both surgeon experience and published evidence, and how such complications may be best addressed.
- 1. Five-year investigational device exemption (IDE) study data, which is long-term data, is readily available to support the utilization of lumbar total disc replacement (TDR) in the appropriately selected patient.
- 2. The published data on commercially available lumbar TDR technology used in treatment of degenerative disc disease (DDD) demonstrate:
Discussion topics that were included as part of the initial questionnaire, or discussed in-depth at the meeting, included observed challenges with lumbar TDR, patient selection factors and complications, comparative complication rates for TDR and fusion, timing of their occurrence, and techniques to help address complications. For this discussion piece, late complications are noted to include those such as wear debris-induced osteolysis, ASD, and device failures, including implant migration impingement and subsidence. Two consensus statements were developed from this session.
The definition of “long-term” data was deliberated extensively by the panel. Agreement on a definition for this was important for arriving at a consensus on matters pertaining to the complication risk for lumbar TDR. The panel communicated several stipulations that should be considered in defining long-term data, such as the time period when most complications are observed, the follow-up periods used in randomized trials, the need for data to be published, and Food and Drug Administration (FDA) criteria on timing for safety and durability of efficacy evidence. Results from the survey demonstrated that while TDR device-related complications are rare, surgeons typically observe them within weeks to a few months after the index procedure. One panel member noted that complications sometimes occur 1 to 2 years after the procedure in certain especially rare cases. An important point raised in the discussions was that most complications occur within 5 years; therefore, most ASD would be expected to occur within a 5-year follow-up period, which is 3 years longer than the FDA requirement for efficacy results. Through these deliberations, consensus was therefore reached that the 5-year data point should be considered as long-term data in regards to evidence for lumbar surgeries, and that such data are now readily available to support patient access to lumbar TDR as a surgical option.
Some coverage policies have made unsubstantiated claims regarding the long-term complications that could emerge and have raised unfounded questions regarding the biological effects of wear, as well as the effect of the artificial disc on progression of adjacent level lumbar DDD. In response to these concerns, the panel deliberated on the topic of lumbar TDR complications by considering both evidence and practice experience. One panel member stated: “I believe that there have been enough implants world-wide, and for a long enough time to mine that data appropriately.” Another panel member further noted that they “had not seen convincing data that wear of polyethylene inlay is a concern with lumbar TDR.” The survey revealed that certain complications, such as device failures that require revision surgery, were rare in most of the surgeon's practices, with some surgeons reporting zero complication rates. Furthermore, most panel members experienced a reduction in lumbar TDR complications in their practice over time, which was attributed to factors such as experience and advancement in TDR technologies and training.
The panel came to a complete consensus that the published evidence on commercially available lumbar TDR for use in DDD demonstrates significant reductions in ASD and reoperations compared with fusion. Other outcomes were discussed, but these were felt to be the most relevant from a comparative standpoint. The panel also agreed that they have no significant concerns regarding later onset complications with commercially available lumbar TDR devices. The panel stipulated that it was important to qualify these statements with the term “currently available” to eliminate concerns with respect to older, less advanced TDR devices that are no longer on the market. It was discussed that first-generation lumbar TDR technologies have several shortcomings. Comments cited in the survey included “prior generation TDR devices were more difficult to insert as more visualization was required,” and that the “first-generation designs were less forgiving and thus were not appropriate for mass adoption”. In addition, it was noted that “semiconstrained implants have proven to be more reliable than totally nonconstrained implants” and that “there is better initial fixation with newer TDRs.” Further detail on the evidence supporting the safety consensus statements is provided in the next sections.
Level 1 evidence, published in the form of numerous meta-analyses comparing lumbar TDR with fusion, demonstrates a similar or lower risk of complications with lumbar TDR.1–5Table 1 provides a summary of effect estimates for the outcomes of general complications or adverse events, as well as reoperations. At 2 years, the risk of complications was consistently lower for lumbar TDR than for fusion in all published meta-analyses, as indicated by odds or risk ratios less than 1.0. Reoperation rates were aligned with the overall complication findings. Hiratzka et al2 recently conducted a long-term meta-analysis and reported that the risk of adverse events related to surgery for TDR patients was half the rate observed for fusion, and this difference was maintained at 5 years. The relative risk (RR) of reoperation was also 1.7 times higher for fusion than for TDR at 2 years (RR = 1.7; 95% confidence interval [CI] 1.1–2.6), although reoperation risk was comparable at 5 years (RR = 1.1; 95% CI 0.57–2.1).2 However, the authors noted that there were inconsistencies in the definition and reporting of adverse events across studies, making conclusions difficult. More recently, Zigler et al5 conducted a 5-year meta-analysis of four randomized trials. The safety outcome assessed was risk of reoperations, defined as device-related failures resulting in the subsequent surgical interventions of reoperation, revision, removal or supplemental fixation. Using this definition, the study reported that there was approximately half the risk of reoperations with lumbar TDR than with fusion over time.5 Another qualitative systematic review reported a lower range for reoperation rates with lumbar TDR (3.7%–11.4%) than with fusion (5.4%–26.1%).6 Furthermore, two meta-analyses reported a significantly reduced risk of ASD with lumbar TDR versus fusion1,7 (see Figure 1). These low rates of ASD with TDR are corroborated by a systematic review of 3 to 22 years of pooled follow-up data from single-arm studies.8
Long-term observational studies are generally aligned with findings from the recent meta-analyses and 5-year randomized controlled trials (RCTs). As indicated previously, there are numerous studies that evaluate lumbar TDR for 5 or more years in duration. Several of these are observational studies, including commercially available lumbar TDR implants, which have reported a low risk of long-term complications with lumbar TDR (e.g., device migration, subsidence, reoperations).9–12 Siepe et al13 conducted a long-term study of the ProDisc-L implant, with a mean follow-up of 7.4 years, and concluded that “fears of excessive late complications or reoperations with TDR cannot be substantiated with the present data.” In a 6-year single-center post-hoc analysis of IDE data including both the activL and ProDisc-L devices, implant subsidence was reported to be low for both devices (activL: 1.4%, ProDisc-L: 1.9%).14
There are now six RCTs, five of which are IDE trials, of lumbar TDR for the treatment of DDD with long-term 5-year follow-up data. Although definitions of adverse events varied across studies, the body of evidence demonstrates a good safety profile for lumbar TDR devices over this follow-up duration. Overall, very low device migration or subsidence rates were observed. In fact, in one RCT, lumbar fusion was reported to have a significantly greater number of severe or life-threatening adverse events compared with TDR (i.e., 0.58 vs. 0.38 per patient respectively; P = 0.0364).15 In this same study, lumbar fusion patients were three times more likely to have ASD than TDR (see Figure 1). Across trials, low rates of reoperations, and extremely low levels of particulate wear debris complications, were observed over 5 years.
Although the focus of the panel discussions was on the evidence that supports the long-term safety of lumbar TDR, additional complication considerations arose as part of discussion and questions within the survey. In brief, the evidence demonstrates that success with lumbar TDR is improved with appropriate patient selection.16,17 For example, Park et al16 reported that there is a higher risk of revision surgeries in those not adherent to strict selection criteria for lumbar TDR. Many panel members confirmed the importance of adhering to selection criteria to minimize patient complications. A common theme generated through discussions and survey results was the use of experienced access surgeons, as well as tailored small incisions to help address complication risk. Common procedural challenges, when they do occur, included gaining full access to the disc space, ensuring an adequate release, and precisely positioning and sizing the implant. Use of experienced and trained surgeons for access was considered important to address these challenges. Additional techniques suggested to help minimize risk included having good intraoperative imaging, and maintaining appropriate imaging follow-up with specific measurements for potential migration. A detailed guideline of optimal techniques is not within the current scope of this article; however, as one surgeon noted, “good access, good visualization, a good release, and good judgment” are the bases for successful TDR procedures in the subpopulation of DDD sufferers who are candidates for TDR.
In summary, in reviewing the body of short and long-term evidence on lumbar TDR technology and considering the panel members’ practical experience, consensus opinion of experienced spinal surgeons was that lumbar TDR is well tested with a sufficient evidence base to support the safety of this technology for patients meeting well-established selection criteria.
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