Key Questions Addressed

We address four Key Questions in this report. These questions are presented below:

1. What are the patient inclusion and exclusion criteria used in studies of decompression therapy?
2. What are the efficacy or effectiveness outcomes measured in studies of decompression therapy? Are the efficacy/effectiveness outcomes measured in studies of decompression therapy comparable to those used in studies of other non-surgical modalities for chronic low back pain due to a herniated disc or degenerative disc disease?
3. Is decompression therapy a safe and effective treatment of chronic low back pain due to herniated disc or degenerative disc disease?
   1. Do patients with chronic low back pain (due to a herniated disc or degenerative disc disease) who are treated with decompression therapy have more, less, or the same level of pain relief than patients who are treated with other therapies?
   2. Do patients treated with decompression therapy for chronic low back pain due to a herniated disc or degenerative disc disease utilize more, less, or the same number of adjunct/chronic therapies, (e.g., medications, bracing) than patients treated with other therapies?
   3. Do patients treated with decompression therapy for chronic low back pain due to a herniated disc or degenerative disc disease return to work more quickly than patients treated with other therapy?
   4. If the therapy is effective, what is the duration of relief achieved?
   5. If the therapy is effective, what are the patient characteristics/indications of those for whom it appears to work? Is the therapy effective for the Medicare population (over 65 years of age)?
   6. If it works, which, if any, particular decompression protocol provides the most pain relief?
4. What complications, harms, and adverse events associated with decompression therapy have been reported?
   1. Do conditions prevalent in the older Medicare population (such as osteoporosis, etc.) increase the risk of adverse events with decompression therapy?

The four Key questions are depicted in the Figure as numbers within a circle.

Figure 1

Analytical Framework.

Study Inclusion/Exclusion Criteria

We selected the studies that we consider in this report using a priori inclusion criteria. As mentioned above, arriving at these criteria before beginning the analysis is one way of reducing bias. We developed different inclusion criteria for each question that this report addresses.

Literature Searches

One characteristic of a good technology assessment is a systematic and comprehensive search for information. Such searches distinguish systematic reviews from traditional literature reviews. Traditional reviews use a less rigorous approach to identifying and obtaining literature and allow a reviewer to include only articles that agree with a particular perspective, and to ignore articles that do not. Our approach precludes this potential reviewer bias because we obtained and included articles according to explicitly determined a priori criteria. This was particularly important for Key Question 3, the assessment of efficacy. We discuss articles that we included in the Synthesis of Results section.

Identification of Evidence Bases

The selection process used to identify the articles that comprise the evidence base for the key questions addressed in this report is presented in Figure 2. Our searches identified ten articles that potentially addressed Key Questions 1 through 4. Of these ten articles, we retrieved seven. Three additional studies(8–10) were brought to our attention by reviewers, for a total of ten included studies (Table 3). These three additional studies did not meet criteria for Key Question 3 as they were not comparative studies and two had fewer than 10 patients, but we did review them for information relevant to the other Key Questions. Eight included articles addressed Key Question 1, nine included articles addressed Key Questions 2, three included articles addressed Key Question 3, and all ten articles were reviewed for adverse events, Key Question 4.

Figure 2

Summary of Article Selection Process.

Table 3

Evidence Base.

Evaluating the Strength of the Evidence

We used the ECRI strength-of-evidence system to evaluate the stability and strength of a body of literature (shown in Appendix B). This system considers numerous components of the evidence, including the internal validity of the trials, the size of the evidence base, consistency and robustness of trial results, and magnitude of the effect size. The system outputs two ratings. One is a stability rating (high, moderate, low, unstable) for a quantitative estimate addressing the question “How well does it work?” The other is a strength rating (strong, moderate, weak, inconclusive) for the evidence about the qualitative question “Does it work?” This distinction allows an evidence base to be considered weak in terms of the quantitative estimate of effect (e.g., if estimates vary widely among trials) but strong or moderate with respect to the qualitative conclusion (e.g., if all trials nevertheless demonstrate the same direction of effect). The system also employs a priori judgments, meta-analyses, and sensitivity analyses to provide sound bases for evidence ratings. Interpretations of the terms that define the strength of evidence (strong evidence, moderate evidence, weak evidence, and inconclusive evidence) and stability ratings (high stability, moderate stability, low stability or unstable) are presented in Table 4.(43)

Table 4

Definitions of Strength and Stability of Evidence.

The 10 decision points that comprise the ECRI strength-of-evidence system address five general aspects of the evidence (domains): quality, quantity, consistency, robustness, and magnitude of treatment effect. Quality refers to the degree of potential bias in the design or conduct of studies. Quantity refers to the number of studies and the number of patients enrolled in the studies. Consistency addresses the degree of agreement among the results of available studies. Robustness refers to the degree to which the findings are susceptible to being overturned by future studies. Magnitude of treatment effect concerns the quantitative amount of benefit (or harm) that patients experience after treatment. The ECRI strength-of-evidence system includes all five of these aspects when assessing the strength of the evidence (see Appendix B).

We apply each kind of rating to the body of evidence that addresses each outcome, not to individual studies. We also rate on an outcome-by-outcome basis. Four primary factors determine our ratings for both strength and stability; the quality, quantity, robustness, and consistency of the evidence. Under certain circumstances, the size of the treatment’s effect, and whether mega-trials are available also influence our ratings of the evidence underlying qualitative conclusions.

Statistical Methods

The current evidence base was too small to allow us to employ statistical methods such as meta-analysis.

Characteristics of Included Studies

Information on study characteristics is presented in Table 5. We present more complete details of these studies (study design details, information on enrolled patients, outcome data, and other relevant information) in the evidence tables that comprise Appendix D.

Table 5

Characteristics of Included Studies.

We reviewed a technology assessment prepared for the Australian Medical Services Advisory Committee (MSAC) in support of health care financing decisions.(4) Three of the studies included in this report were controlled trials: a randomized controlled trial (RCT), a controlled trial with an inappropriate (sequential) method of randomization, and one non-randomized controlled trial.(1,3,6) One included study was a case series that reported on outcomes from 778 patients who received vertebral axial decompression therapy in one of 22 centers across the United States.(5) Another case series sought to examine long-term (12-month) outcomes in a group of patients who underwent IDD Therapy® in conjunction with “an expanded physical therapy component.”(10) Three additional case series reported physiological outcomes. These included current perception threshold (CPT) as an indicator of nerve root decompression,(7) changes in intradiscal pressures during decompression therapy(8), and dermatomal somatosensory evoked potentials.(9) Finally, we included a case report describing an adverse event that occurred during vertebral axial decompression therapy.(2)