Mechanisms of Chiropractic Spinal Manipulation for Chronic Low Back Pain

Pain intensity will be measured by showing patients a numerical rating scale from 0 (no pain at all) to 100 (maximum possible pain), and patients will rate with a number their current pain, highest, lowest and average during the 7 previous days (baseline) or the days following the previous session.

The Oswestry Disability Index (ODI) questionnaire provides the level of self-reported disability in activities of daily living (ADL) related to low back pain. It includes 10 items rated on a Likert scale from 0-5. The total range of possible scores is from 0-50, where 0 means no disability at all, and 50 is the maximal disability.

The Pain Catastrophizing Scale (PCS) provides the level of catastrophizing beliefs and emotions that a person has with regards to his/her own pain experience, in this case, low back pain. It includes 13 items rated on a Likert scale from 0-4. The total range of possible scores is from 0-52, where 0 is the lowest possible level of catastrophizing and 52 the highest. This scale will also be used in healthy participants.

The Central Sensitization Inventory (CSI) identifies key symptoms associated with central sensitization and provides a quantification for the degree of these symptoms, which help to identify a central sensitization phenotype patients with chronic pain. It includes 25 items rated on a Likert scale from 0-4. The total range of possible scores is from 0-100, where 0 is the lowest possible level of central sensitization symptoms and 100 the highest. Additionally, the CSI asks one more question related to the previous diagnosis of either one of 10 conditions that have been related to central sensitization. this part is informative and is not used for scoring purposes. This scale will also be used in healthy participants.

Pressure pain thresholds (PPTs) are part of quantitative sensory testing. The aim is to identify the threshold and the sensitivity to suprathreshold pressure stimulation in different areas of the patients' bodies. A digital algometer will be used (Wagner Force Dial FPX, Greenwich, CT, USA) to measure PPTs in the lumbar segment of greatest pain for each patient (2cm lateral to the spinous process or the posterosuperior iliac spine if applicable) locally, in the dermatome of this segment in the lower limbs, at the regional level four segments cranial from the segment of greatest pain, and remotely at the level of the thenar eminences. Measures will always be taken bilaterally two times, and averaged. At that time, the patient will rate in a numerical rating scale from 0 to 100 the intensity of the first painful stimulation (suprathreshold sensitivity). For healthy participants, pressure pain thresholds will be measured at every segment of the lumbar spine and in the thenar eminences.

Tumor Necrosis Factor alpha (TNF-a) is a pro-inflammatory cytokines that have been involved with different stages of low back pain. First morning urine samples will be taken from patients and healthy participants at the beginning and the end of the trial period. Samples will be stored at -20ºC and concentrations will be measured with a sandwich ELISA. TNF-a will be the only cytokine used for before and after changes.

The Beck Depression Inventory (BDI-II) identifies key symptoms associated with clinical depression and provides a quantification for the presence and severity of depressive symptoms. It includes 21 items rated on a Likert scale from 0-3. The total range of possible scores is from 0-63, where 0 is the lowest possible level of depressive symptoms and 63 the highest.This scale will also be used in healthy participants.

The Generalized Anxiety Disorder (GAD) identifies key symptoms associated with generalized anxiety disorder and provides a quantification for the presence and severity of these symptoms. It includes 7 items rated on a Likert scale from 0-3. The total range of possible scores is from 0-63, where 0 is the lowest possible level of depressive symptoms and 21 the highest. The threshold of 10/21 is used to diagnose generalized anxiety disorder. This scale will also be used in healthy participants.

Participants will rate in a numerical rating scale their expectations of pain relief at the end of the trial. It will consist on a scale from -100 (maximum reduction in current pain) to 0 (no change) to +100 (maximum imaginable pain increase).

Chronic pain patients will describe whether their pain is episodic (pain-free periods of at least 4 week duration) or fluctuating (no pain-free periods of at least 4 week duration)

Pain duration at baseline since the onset of low back pain, described in months

Patients will draw in a digital application (Symptom Mapper) the extent of their body affected by pain.

The presence of pain in the lower extremity concomitant or related to low back pain will be recorded as Yes/No answer.

The use of pain medication (apart from the ones referred to in the exclusion criteria) will be reported as Yes/No answer, and a description will be noted.

A set of clinical criteria (defined by Smart et al., Manual Therapy 2015 and Nijs et al., Pain Physician 2015) will be used to classify patients as having central sensitization pain, this first one will be answered with a "Yes" or "No" regarding whether their pain is disproportionate to damage to lumbar tissues.

A set of clinical criteria will be used to classify patients as having central sensitization pain, this second one will be answered with a "Yes" or "No" regarding whether their pain has a diffuse anatomical distribution.

Biological sex (Male or Female)

Age (measured in years)

Education level (3 categories: basic, high school or university level)

The presence of other chronic disease comorbidities will be assessed as Yes/No answer.

Type of adverse reaction to treatment (muscle stiffness, increased pain, radiating discomfort, and others - described by the patient)

Onset of adverse reaction to treatment (immediately, up to 24 hours, or more than 24 hours after the previous session)

Duration of adverse reaction to treatment (minutes, hours (< 24 hours), 24-48 hours, or > 48 hours)

Severity of adverse reaction to treatment (very mild, mild, moderate, severe, very severe)