October 2022

Limited prognostic value of pain duration in non-specific neck pain patients seeking chiropractic care

Guillén D, Guekos A, Graf N, Humphreys BK, Peterson C & Schweinhardt P

Faculty of Medicine, University of Zurich; Department of Health Sciences and Technology, ETH Zurich; Integrative Spinal Research, Department of Chiropractic Medicine, Balgrist University Hospital, University of Zurich, all in Switzerland

European Journal of Pain 2022; 26(6): 1333-1342.

Chronic pain has been defined as persistent or recurrent pain lasting longer than several months (typically, 3 months). The 3-month cut-off, however, has been challenged as a prognostic factor as well as its use in clinical decision making (1). Neck pain in general has been shown to be one of the leading causes of disability worldwide and its prevalence and ‘years lived with disability’ is increasing (2, 3).

Pain duration as a prognostic factor relating to clinical outcome in neck pain patients has been reported by several researchers. However, patients in these studies mainly had pain of any duration and were categorized into acute, sub-acute and chronic, but with categories defined as having varying durations. Cecchi et al. (4) found that pain duration was not a significant prognostic factor in chronic (6 months or more) neck pain patients.

Studies that reported pain duration as influencing outcomes typically determined whether there was an increased risk associated with longer pain duration versus a shorter pain duration, but this type of comparison does not inform about the amount of variance in outcome that is explained by pain duration. Variance is a measure of how much a data set is spread out. Because of this and other methodological weaknesses of previous studies, several questions remain.

The focus of the current study was to investigate whether pain duration has an influence on treatment outcome when only chronic patients with pain duration longer than 3 months are considered.

The authors also assessed in patients of any pain duration: 1) how much variance in outcome is explained by pain duration; and 2) whether a model identified in a training dataset predicts outcome in independent data.

Eighty-one chiropractors (31% of the Association of Swiss Chiropractors) contributed data on 851 neck pain patients, but only 720 were ultimately used because 131 patients overlooked the primary predictor of pain duration.

Patients’ average pain duration at baseline was 62 weeks and the average Numerical Rating Scale (NRS) pain intensity was 5.8. The influence of pain duration on outcomes was tested for all the follow-up time points as a statistical predictor of outcome, but pain duration was not significantly related to outcome in any of the analyses that were performed. Patients with short (3–6 months) and long (over 4 years) pain chronicity were compared, with no significant differences found except at the 1-week follow-up.

The amount of variance in outcome that was explained by pain duration when patients of any pain duration was calculated, showed that the amount of variance explained was small (between 3% and 33%). Nonetheless, most patients improved at all follow-up time points, indicated via the patient's global impression of change (PGIC) reported as ‘improved’ and/or a positive change in NRS score.

When only chronic patients were considered, pain duration was NOT a predictor of outcome in neck pain patients. In patients with pain of any duration, pain duration explained some of the variance in outcome, particularly for PGIC at the 1-week follow-up.

Given the large number of patients that participated in this study and the finding that neck pain duration was not an important predictor of pain outcomes in chronic patients, we as clinicians should remain optimistic with patients about their potential outcomes with treatment, regardless of their pain duration.

This was an observational prospective cohort study of neck pain patients in Switzerland which involved all active members of the Association of Swiss Chiropractors (260 members). The chiropractors received instructions on the study by email and had them explained during a mandatory annual continuing education convention. Data were collected between October 2009 and March 2015.

The chiropractors invited their new patients to participate in the study using the following inclusion criteria: over 18 years of age, neck pain of any duration, and not having undergone chiropractic or manual therapy in the previous 3 months. Patients with pathologies of the cervical spine that are contraindications to chiropractic manipulative therapy were excluded. Participating patients were thus considered to be suffering from ‘non-specific neck pain’.

The initial data were collected by the chiropractors and office assistants prior to the first treatment and then at 1 week, 1 month, 3 months, 6 months and 1 year. Research assistants at the university collected the follow-up data via telephone interviews. To reduce potential for response biases, the research assistants did not know the patients or the referring chiropractors.

Baseline clinical and follow-up data included measures such as pain duration, number of previous neck pain episodes, Numerical Rating Scale (NRS) of pain intensity, Bournemouth Questionnaire, patient's global impression of change (PGIC) scale, and percentage change score.

The participating chiropractors utilized the treatment methods they thought were indicated by the case history and physical examination findings. The most common treatment modality that is used by Swiss chiropractors is the diversified technique, which is a high-velocity and low-amplitude (HVLA) thrust type of spinal manipulation. Other commonly used modalities included advice on activities, trigger point therapy, therapeutic exercises, mobilization techniques and physical therapy modalities.

This study was relatively large and included chiropractic patients who were followed over a long period of time using valid outcome measures. Its findings are therefore applicable to practitioners who treat chronic neck pain patients when developing treatment plans and explaining expected outcomes to patients.

This was a pragmatic observational study in which Swiss chiropractors utilized their personal treatment regimens which may differ from other chiropractors in other locations. Patients were not randomized and there were no control or comparison groups. These factors limit the ability to generalize the results to other neck pain populations.