RRS Education Research Reviews DATABASE

Research Review By Dr. Michael Haneline©

Date Posted:

Feb. 2009

Study Title:

Benign adverse events following chiropractic care for neck pain are associated with worse short-term outcomes but not worse outcomes at three months


Rubinstein S et al.

Author's Affiliations:

VU University Medical Center, Amsterdam, the Netherlands

Publication Information:

Spine 2008; 33(25): E950-E956.

Background Information:

The type, frequency, duration, and intensity of benign adverse events following neck and back manipulation have previously been described in the literature. However, little is known about the association of these benign adverse events to patient outcome.

The one study that did look into this relationship by Hurwitz et al. (1) reported that patients who experienced adverse events were less satisfied with care and less likely to have clinically meaningful improvements in neck pain and disability at every follow-up measurement throughout the 6-month study period.

However, the findings of the Hurwitz et al. study contradicted other studies, which have for the most part reported that adverse events following neck manipulation were of short duration and did not have significant effects on patients’ activities of daily living.

Because of this discrepancy, the current study was designed to examine the relationship between benign adverse events and outcomes (perceived recovery, neck pain, and neck disability) in a group of neck pain patients who received chiropractic care.

Pertinent Results:

A total of 529 patients were included in the study (529 qualified out of 579 recruited). Almost all of the patients (96%) returned for a second visit, most (87%) returned a fourth visit, and 90% of them returned the follow-up questionnaire at 3 months.

Adverse events after any of the first 3 treatments were reported by 56% of the study population. A much smaller percentage (13%) reported an adverse event that was considered to be severe in intensity. Musculoskeletal or pain-related adverse events were the most common type reported. None of the reported events were considered serious.

In general, patients with more neck pain and/or stiffness after the first visit were less likely to report recovery.

Patients who experienced an adverse or intense adverse event after any of the first 3 visits reported significantly more neck pain at the fourth visit, and were less likely to experience recovery. However, the difference in neck pain between those who experienced an adverse event and those who did not was so small that it was not clinically meaningful.

When only considering those patients who had an intense adverse event after any of the first 3 visits, they had significantly more neck pain and disability at the fourth visit and were less likely to report recovery. This difference was clinically meaningful regarding neck disability at the fourth visit.

Overall, patients who experienced an adverse event following their first visit were less likely to report recovery at the fourth visit. However, they did not have significantly more neck pain or disability than those who did not report adverse events. At 3 months follow-up, patients who experienced an adverse or intense adverse event after any of the first 3 treatments were not more likely to experience increased neck pain or disability, nor were they less likely to report recovery.

The authors conducted a post hoc sensitivity analysis of the data to determine whether inclusion of the independent variable “worsening of the neck pain” influenced the association between the central determinant, “any type of adverse event following any of the first 3 visits,” and the outcome variables neck pain and neck disability. However, no statistically significant associations were found.

Clinical Application & Conclusions:

The “take home” message from this article is that while patients in this study commonly noticed adverse events following chiropractic care for neck pain, they were benign and did not negatively affect outcomes at 3 months. None of the adverse events were serious (i.e. 0 out of 4,891 treatment sessions). These findings add strength to a statement made in one of the authors’ previous reports on this data that “the benefits of chiropractic care for neck pain seem to outweigh the potential risks.” (2)

Moreover, it was only the “intense” variety of adverse events that were found to be associated with clinically-relevant increased neck disability in the short term (i.e. at the fourth visit), and, as was mentioned earlier, only 13% of the patients experienced an intense adverse event.

The authors concluded that their findings differed from those of Hurwitz et al. (1) who found that neck pain patients receiving chiropractic care who had adverse events reported worsening of symptoms not only in the short-term, but also worse outcomes at 6 months. Their findings were in agreement several other studies, however, which in general reported that adverse events following chiropractic or spinal manipulative therapy are common, but they mostly resolve in less than 24 hours and have little effect on activities of daily living.

Study Methods:

This was a practice-based study made up of 79 volunteer chiropractors who were solicited from members of the Netherlands Chiropractors’ Association. The participating chiropractors recruited neck pain patients from their practices on their first visit and then followed up with evaluations at the second and fourth visit, as well as at 3 months. The type, as well as the number of treatments provided was at the discretion of each individual chiropractor.

Patients were included in the study if they had neck or neck-related pain, were between 18 and 65 years of age, and had not received chiropractic care or manual therapy in the previous 3 months. Patients were excluded if they had a red flag condition (e.g., tumor or infection) or any other condition thought to be a contraindication for cervical spine manipulation.

The participating chiropractors completed questionnaires at the beginning of the study regarding their age, gender, college of chiropractic education and year of graduation, years of experience, and types of techniques and/or therapies commonly used.

The patients provided information at baseline regarding their self-reported general health, expected treatment effectiveness, and fear of or apprehension about treatment. The study’s outcome measures were as follows:
  • neck pain in the 24 hours preceding the initial visit on an 11-point numerical rating scale (NRS)
  • disability via the Neck Disability Index (NDI)
  • perceived recovery, ranging from the patient being much worse to completely improved on a 6-point Likert scale
  • treatment satisfaction
  • adverse events following treatment
The patients were queried about adverse events at their second and fourth visits. The definition of an adverse event included either a new related complaint that was not present at baseline, or a worsening of neck pain or any other existing complaint by >30% over the previous visit. An adverse event was considered to be “intense” when it resulted in pain that was >8 in intensity on the 11-point NRS.

A list of potentially confounding variables were selected for inclusion in the statistical analysis based on the authors’ previous work (2). Examples of some of these variables included patient variables (e.g. age and gender), practitioner variables (e.g. age, years of experience and chiropractic school attended), as well as treatment variables (e.g. the number of manipulative attempts, whether upper cervical manipulation was used, and whether rotation was used).

Study Strengths / Weaknesses:

The researchers did an excellent job of carrying out the practice-based research (PBR) design that was utilized; a research design that is often difficult for researchers to implement. Participating practitioners typically donate their services in PBR. Accordingly, some of them, for various reasons, do not feel the need to fulfill their commitment to recruit and/or evaluate patients. In spite of these obstacles, both the rate of practitioner participation and patient follow-up were very high in this study.

The group of patients was large (529) and follow-through was excellent. For comparison, the only other study that has looked at adverse events in a population of neck pain patients treated by chiropractors only included 48 patients who were randomized to manipulation and reported an adverse event.

The authors pointed out several limitations of this study, including the lack of a control group, which they indicated was the most important one. Without a control group it is not possible to completely rule out natural history as the cause of the observed outcomes.

Respondent bias by the participating chiropractors was another potential limitation, wherein the participating chiropractors may have been more cautious and conservative than those who did not participate. Participants may have been more cautious because they did not want to bring about an adverse event in their patients, knowing the results might reflect poorly on the chiropractic profession, as well as on themselves.

Another weakness concerns the fact that a PBR design was utilized. PBR has several strengths, including its economic feasibility and the way patients are managed, which is usually similar to how typical chiropractors manage their patients. This makes the study’s external validity high, which means the results of the study are applicable in other circumstances. However, PBR is strictly an observational research design, as compared with randomized controlled trials (RCTs) which qualify as experiments and are capable of showing cause and effect relationships. There is also much less control over the practitioners in PBR than in a RCT.

As a result of PBR’s weaknesses, it is generally more difficult for practitioners to rely on the evidence that results from PBR studies. Moreover, they are usually thought of as preliminary investigations, to be confirmed by follow-up studies using more rigorous research designs.

Additional References:

  1. Hurwitz EL, Morgenstern H, Vassilaki M, et al. Adverse reactions to chiropractic treatment and their effects on satisfaction and clinical outcomes among patients enrolled in the UCLA Neck Pain Study. J Manipulative Physiol Ther 2004; 27:16–25.
  2. Rubinstein SM, Leboeuf-Yde C, Knol DL, et al. The benefits outweigh the risks for patients undergoing chiropractic care for neck pain: a prospective, multicenter, cohort study. J Manipulative Physiol Ther 2007; 30:408–18.

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