Key Question 1. What are the patient inclusion and exclusion criteria used in studies of decompression therapy?

Eight articles addressed Key Question 1.(1,3,5–10) The only patient inclusion criterion consistently listed across of these studies was that enrolled patients must have suffered from chronic low back pain related to radiographically confirmed disc degeneration or herniation. Some studies included patients with facet joint arthritis or facet syndrome. Common exclusion criteria described in the three studies reporting them were tumor, infection, spinal instability, and surgical implants. Other reported inclusion/exclusion criteria were unique to individual studies.

Of particular relevance to the Medicare population is the fact that one included study specifically excluded patients with “severe osteoporosis,”(1) and the presence of osteoporosis is considered a contraindication. Two studies indicated that patients over the age of 65 were included.(1,10)

Key Question 2. What are the efficacy or effectiveness outcomes measured in studies of decompression therapy? Are the efficacy/effectiveness outcome 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?

Eight included studies that enrolled a total of 1,032 patients and the health technology assessment(4) addressed Key Question 2.(1,3,5–10) The most frequently reported health outcomes evaluated by these studies of decompression therapy were change in pain score or percent improvement in pain (six studies) and functional outcome (three studies). These outcomes are also commonly assessed in studies of other non-surgical modalities for chronic low back pain due to herniated disc or degenerative disc disease. Other vertebral decompression studies reported possible surrogate outcomes such as intradiscal pressure(8), current perception threshold (CPT),(7) and dermatomal somatosensory evoked potentials (DSSEPs)(9) as indicators of nerve root decompression.

A number of outcomes which were evaluated in studies of other non-surgical modalities for chronic low back pain were not evaluated by studies of decompression therapy. These include: absenteeism, return to work, overall health, analgesic consumption, disability rates, and quality of life.

Key Question 3. Is decompression therapy an effective treatment for chronic low back pain due to herniated disc or degenerative disc disease?

1. Do patients with chronic low back pain (due to 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 adjunctive 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 therapies?
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?

Three studies that enrolled a total of 225 patients met inclusion criteria and addressed Key Question 3.(1,3,6) Two of the studies evaluated the VAX-D system(1,3); the remaining study evaluated the Decompression Reduction Stabilization (DRS®) system.(6) One included study was a randomized controlled trial,(6) one was an unblinded controlled trial with an inadequately described method of randomization,(3) and the third study was a non-randomized controlled trial that evaluated the effect of different “doses” of VAX-D) therapy.(1)

An evaluation of the quality of the three included studies found two of the studies to be of low quality.(3,6) The remaining study(1) was found to be highly susceptible to bias (e.g., did not ensure baseline comparability of the groups) and was not considered further in addressing Key Question 3.

One of the remaining two studies compared VAX-D therapy to transcutaneous electrical nerve stimulators (TENS) therapy and the other compared DRS® to traction therapy. Although both studies reported evidence in favor of decompression therapy (significant reductions in pain scores or patient reports of improvement in symptoms), the low quality and low quantity of evidence precludes us from drawing an evidence-based conclusion concerning the efficacy of decompression therapy for treating chronic low back pain at this time. One study described six-month follow up for a subset of patients(3), otherwise, none of the sub-questions could be answered. Neither study included any patients over the age of 65 years.

Key Question 4. What complications, harms, and adverse events associated with decompression therapy have been reported?

1. Would the characteristics of the Medicare population (osteoporosis, etc.) increase the likelihood of adverse events compared to the trial populations?

All ten studies were evaluated for reports of adverse events associated with VAX-D or decompression therapy. The quality and generalizability of the information was not formally evaluated because we included case reports and case series in this evidence base. Uncontrolled studies cannot be used to determine causality or to estimate frequencies of adverse events; they can only be used to generate a list of adverse events possibly attributable to the device.

Adverse events were reported to occur in association with decompression therapy (one case report of an enlargement of an existing disc protrusion and several reports of treatment-related pain). However, inconsistencies in the reporting of adverse events limits one’s confidence in the true extent of treatment related adverse events. For example, according to a Medical Services Advisory Committee (MSAC) report presented to the Australian government, which included unpublished studies provided by the manufacturer,(4) approximately 10% of individuals who undergo VAX-D therapy are unable to tolerate the procedure. None of the clinical trials included in the present report, including the large case series of Gose et al.(5) (which enrolled 778 patients), reported that any patients were unable to tolerate treatment. Of note, however, this case series was limited to patients who had received at least 10 treatments. Currently there is no evidence to establish whether the common characteristics of the Medicare population (such as the presence of undiagnosed osteoporosis) would increase the likelihood of adverse events when compared to the trial populations. It should be noted that the literature produced by providers of decompression therapy lists osteoporosis as a contraindication for this therapy.