Thirty patients (52.6%) stated that they would choose the same treatment again if they were faced with the same problem. Seven patients (12.3%) would probably choose the same treatment again, seven patients (12.3%) would probably or definitely not choose the same treatment again, and 13 patients (22.8%) were indecisive (SDC Table 6, http://links.lww.com/BRS/B268). The distribution of responses between the revision and no revision groups was not statistically significantly different (P = 0.730).
Several publications on clinical outcomes after lumbar TDR have been reported2,6–10,14,16–18,20 including results from randomized controlled trials comparing TDR to fusion1,3,13 and systematic reviews and meta-analyses on the topic.26–29 However, the number of studies on the long-term efficacy of TDR are still limited. This study aims at assessing the long-term clinical outcomes after TDR with ProDisc II.
Several short-term and mid-term studies on TDR have reported statistically significant improvement in clinical outcomes after TDR.2,6,7,9,10,14,18,19 Scott-Young et al18 reported statistically significant improvements in VAS, Oswestry Disability Index (ODI), and SF-36 PCS. Park et al2 also reported significant improvement in VAS, ODI, and SF-36 at all follow-up stages compared to baseline. However, they observed a maximal effect at 2 years’ follow-up and a slight decline in outcome at the last follow-up compared to 2 years’ follow-up. In addition, Lazennec et al14 found an early significant improvement of VAS at 3 months and at 6 months for ODI. VAS and ODI remained stable hereafter.
A number of randomized controlled trials have reported similar result after TDR compared to fusion at short-term follow-up.1,3,13 Clinical outcomes improved significantly at follow-up compared to baseline for both groups, suggesting either TDR or fusion as treatment option for patients with DDD.1,3 Berg et al13 found a better outcome at 1-year follow-up for patients treated with TDR, whereas patients treated with fusion improved during the second year postoperatively, although TDR had a larger number of pain-free patients at all follow-up stages. Furthermore, the majority of systematic reviews and meta-analyses reported superior or equal improvement in clinical outcomes after TDR compared with fusion.26,28,29 However, Hiratzka et al27 were unable to make a clear recommendation of TDR over fusion, owing to an inadequate and high variation in reporting of adverse events following TDR and fusion.
In a long-term study, Siepe et al17 found a highly significant improvement of VAS and ODI at all follow-up stages after TDR compared to baseline scores. ODI remained stable throughout the entire follow-up period, but a slight deterioration of VAS at the last follow-up was reported, although VAS was still well below baseline level. Other long-term studies have reported similar results with significant improvement in VAS and ODI and overall excellent clinical outcomes.8,16,20
The overall data from this study also reveal highly satisfactory clinical results at follow-up compared to baseline. VAS back pain and leg pain and SF-36 PCS improved significantly at follow-up compared to baseline. The improvement of DPQ D, DPQ P, and DPQ AD was also statistically significant, but DPQ S was not different at follow-up compared to baseline. The SF-36 MCS was worse at follow-up compared to baseline.
Comparing the patients who had a revision with those who did not have a revision, all variables at follow-up, except DPQ AD and SF-36 MCS, were significantly better in the nonfusion group compared to the fusion group (P < 0.05) (Table 5). According to Park et al20 and Siepe et al,17 long-term follow-up is more likely to compromise clinical results. This might explain the less improvement of the variables of the fusion group in relation to its slightly longer follow-up period compared to the nonfusion group. Although the difference in mean follow-up rates between the two groups was little over a year, this was statistically significant. The differences in outcomes between the subgroups might also be because of patient selection before TDR, as patient selection criteria has been clarified since the first TDR in this study was implanted—the patients in the fusion group might not have been appropriate candidates for TDR because of current knowledge.
Our patients’ attitude toward TDR was less positive than reported by Siepe et al17 and Lu et al8 (SDC Table 6, http://links.lww.com/BRS/B268). In Siepe et al's study,17 79.3% of the patients would have the same surgery again if faced with the same condition, 13.0% were unsure, and 7.7% refused. In Lu et al's study,8 78.1% answered “yes,” 15.6% “probably yes,” and 6.3% “definitely not.” The difference might be explained by our revision surgery rate that was higher than reported by Siepe et al.17
Disc Prostheses Survival
Siepe et al17 reported an overall reoperation rate of 16.0% (2.2% owing to adjacent level disc degeneration). However, no data on the level of reoperation are available. David16 reported a reoperation rate of 7.5% for index-level arthrodesis. These rates are similar to that of Sköld et al’ study.1
In this study, 19 patients (33%) had arthrodesis at index level at mean duration 3.5 years (0.5–8.8 years) after index surgery (Table 2). The relatively higher reoperation rate might be because of patient selection criteria for index surgery; thus, many studies highlight that careful patient selection is essential to ensure best possible outcomes after surgery. Improvements in the use of TDR will be further discussed later in the article.
Limitations and Forces
SDC Table 7, http://links.lww.com/BRS/B268 summarizes the essentials of four previously published studies (Park et al's, Siepe et al's, Lu et al's, David's16), addressing the long-term clinical outcomes after TDR. The four studies have some limitations in contrary to the current study with regard to study design, patients enrolled, and follow-up duration.
The number of patients enrolled in a study has a vital influence on the outcome. A larger cohort is therefore preferable in terms of whether the cohort is representative or not. In this study, we had a total of 57 patients, similar to that of Park et al's study20 (54 patients). Our patient cohort was larger than that of Lu et al's8 (32 patients), but smaller than that of Siepe et al's17 (181 patients) and David's16 (106 patients). Although Siepe et al's cohort17 had a larger number of patients, our cohort might be more representative in relation to assessment of long-term follow-up given the mean follow-up period. Our study has a mean follow-up period of 10.6 years (8.1–12.6 years), whereas the follow-up period of Siepe et al's study17 was widely spread, including patients with mid-term follow-up (7.4 years [5.0–10.8 years]). Park et al's study20 also had a widespread follow-up duration, although to a lesser extent (mean 10.0 years [5.1–12.0 years]).
Looking at the study design, Park et al's20 and David's studies16 both have a retrospective design, whereas the current study, Siepe et al's17 and Lu et al's studies8 are prospective cohort studies. The lack of control group and randomization can be prescribed to all the studies, including the current study.
The majority of the studies are expressing clinical outcomes in form of VAS and ODI8,17,20. The current study makes use of VAS, DPQ, and SF-36. Preoperative ODI was not available. In the study of David,16 clinical data on functional status were collected using the Stauffer-Coventry Scale. Given the age of the article, VAS, ODI, and SF-36 were neither validated nor in widespread use at the time of these surgical events.
Many improvements have been made in the use of TDR, since the introduction of arthroplasty in the 1980s16,17. Instruments for implanting the prosthesis and imaging of the spine have improved considerably, as well as patient selection criteria have been assessed.16,17 Indications and contraindications for TDR have been outlined, and some outcome-determining factors have been identified.16,17,20 Also tools for assessment of, for example, clinical outcomes have been developed and validated. This given might explain the tendency of older studies to report less favorable outcomes than that of newer studies.17 Siepe et al17 proposed that the current data of long-term follow-ups have to be interpreted as a “worst case scenario” that includes the initial clinical and technical learning curve during the last 2 decades. Therefore application and comparison of current data to future data should only be made carefully and with the current knowledge in mind.17
Encountering the overall improvement in clinical outcomes of this study and other long-term studies, long-term results of TDR are encouraging and indicate that TDR may be an effective alternative in management of lumbar DDD. Thus, proper patient selection is mandatory. To data, there is still a lack of well-designed, long-term evidence, requiring further investigations addressing both clinical and radiological outcomes. In a future study, we will assess radiologic material collected alongside the clinical data in this study.
- TDR is an alternative surgical treatment for patients with CLBP owing to DDD in the lumbar spine.
- The study revealed overall satisfactory clinical results with statistically significant improvement in VAS and DPQ (except sociability).
- Thirty-three percent of the patients had fusion revision surgery at index level at follow-up.
- The lack of well-designed long-term studies is scarce, thus requiring further studies assessing both clinical and radiological outcomes.
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alternative surgical treatment; arthrodesis; chronic low back pain; degenerative disc disease; clinical follow-up; disc survival; fusion; lumbar spine; spine arthroplasty; surgical intervention; total disc replacement
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