Total disc replacement for chronic low-back pain

Artificial joints have had a remarkable impact in reducing pain and improving function in the knee and hip. But what about joint replacement in the spine? This systematic review set out to determine how total disc replacement compares with other treatments for chronic low-back pain in randomised controlled trials.

The disc is a strong but flexible structure that cushions and separates the bony vertebrae of the spine. Disc degeneration is a nearly universal feature of the aging process. Though there are many theories about the causes of low-back pain, chronic symptoms are often attributed to disc degeneration. So when patients do not improve after nonsurgical care, they sometimes consider surgery to remove a degenerated disc.

The traditional surgical approach in this area is spinal fusion, which involves removing all or part of a degenerated disc and joining the vertebrae above and below it. Previous reviews suggest that fusion surgery can lead to moderate pain relief and modest gains in function.  It appears to be superior to traditional physical therapy—but no better than an intensive rehabilitation program.

An alternative surgical approach is total disc replacement, which involves removing the disc and replacing it with an artificial implant made out of metal and plastic.

We identified seven randomised trials—involving a total of 1474 patients. Only one study compared total disc replacement with nonsurgical treatment, suggesting that surgery resulted in slightly better outcomes than intensive rehabilitation. But this did not translate into a clinically significant advantage that would make a major difference in patients’ lives.

Six randomised trials compared disc replacement with spinal fusion surgery. Most of these studies had a high potential for bias, raising the possibility that they might not have provided a fair test of the treatments under study. These trials found that patients who underwent total disc replacement had slightly better outcomes in terms of back pain and function than those who had fusion surgery. But again the differences did not appear clinically significant.

The review could not find evidence of any other benefits of total disc replacement, and the studies provided no insights on the long-term risks associated with it. Given the gaps in the evidence, the review concluded that the spine surgery community should be prudent about adopting this technology on a large scale.

Authors' conclusions: 

Although statistically significant, the differences between disc replacement and conventional fusion surgery for degenerative disc disease were not beyond the generally accepted clinical important differences with respect to short-term pain relief, disability and Quality of Life. Moreover, these analyses only represent a highly selected population. The primary goal of prevention of adjacent level disease and facet joint degeneration by using total disc replacement, as noted by the manufacturers and distributors, was not properly assessed and not a research question at all. Unfortunately, evidence from observational studies could not be used because of the high risk of bias, while these could have improved external validity assessment of complications in less selected patient groups. Non-randomised studies should however be very clear about patient selection and should incorporate independent, blinded outcome assessment, which was not the case in the excluded studies. Therefore, because we believe that harm and complications may occur after years, we believe that the spine surgery community should be prudent about adopting this technology on a large scale, despite the fact that total disc replacement seems to be effective in treating low-back pain in selected patients, and in the short term is at least equivalent to fusion surgery.

Read the full abstract...
Background: 

In the search for better surgical treatment of chronic low-back pain (LBP) in the presence of disc degeneration, total disc replacement has received increasing attention in recent years. A possible advantage of total disc replacement compared with fusion is maintained mobility at the operated level, which has been suggested to reduce the chance of adjacent segment degeneration.

Objectives: 

The aim of this systematic review was to assess the effect of total disc replacement for chronic low-back pain in the presence of lumbar disc degeneration compared with other treatment options in terms of patient-centred improvement, motion preservation and adjacent segment degeneration.

Search strategy: 

A comprehensive search in Cochrane Back Review Group (CBRG) trials register, CENTRAL, MEDLINE, EMBASE, BIOSIS, ISI, and the FDA register was conducted. We also checked the reference lists and performed citation tracking of included studies.

Selection criteria: 

We included randomised controlled trials (RCTs) comparing total disc replacement with any other intervention for degenerative disc disease.

Data collection and analysis: 

We assessed risk of bias per study using the criteria of the CBRG. Quality of evidence was graded according to the GRADE approach. Two review authors independently selected studies and assessed risk of bias of the studies. Results and upper bounds of confidence intervals were compared against predefined clinically relevant differences.

Main results: 

We included 40 publications, describing seven unique RCT's. The follow-up of the studies was 24 months, with only one extended to five years. Five studies had a low risk of bias, although there is a risk of bias in the included studies due to sponsoring and absence of any kind of blinding. One study compared disc replacement against rehabilitation and found a statistically significant advantage in favour of surgery, which, however, did not reach the predefined threshold for clinical relevance. Six studies compared disc replacement against fusion and found that the mean improvement in VAS back pain was 5.2 mm (of 100 mm) higher (two studies, 676 patients; 95% confidence interval (CI) 0.18 to 10.26) with a low quality of evidence while from the same studies leg pain showed no difference. The improvement of Oswestry score at 24 months in the disc replacement group was 4.27 points more than in the fusion group (five studies; 1207 patients; 95% CI 1.85 to 6.68) with a low quality of evidence. Both upper bounds of the confidence intervals for VAS back pain and Oswestry score were below the predefined clinically relevant difference. Choice of control group (circumferential or anterior fusion) did not appear to result in different outcomes.

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