Tactile Acuity in Experimentally Induced Acute Low Back Pain
Condition: Acute Pain; Low Back Pain
MeSH terms: Back Pain; Low Back Pain; Acute Pain
Study type: Interventional

Summary: 
      The purpose of this study is to determine whether experimentally induced acute low back pain
      might lead to alteration in lumbar tactile acuity measured in region affected by pain
      compared to pain-free side and pain-free controls.
    

Detailed description: 
      Healthy male participants will be recruited at the Academy of Physical Education in Katowice.
      Each participant will be assessed only once. All participants will be asked to provide
      written informed consent for participation prior to the experimental procedure and will be
      naïve to the experimental hypothesis. The plan for this research project has been previously
      approved by the local bioethical committee.

      Between-subject (real-injection, sham-injection and control group) and within-subject
      (assessment 1 versus assessment 2 and 3) design will be used for the purpose of this
      experiment. After the screening procedure and preparation phase, participants will be
      randomly assigned to one of three groups: control, saline injection or sham-injection. Groups
      will differ only in terms of the specific manipulation: the experimental group will receive
      intra-muscular saline injection, the sham-injection group will be stimulated by pinprick
      sensation produced by a PinPrick device. No manipulation will take place in the control group
      allowing to control for the learning effect. In fact, participants will be informed that the
      study includes only two branches so they can be assigned either to the group with pain evoked
      as a result of an injection or to the control group without any noxious stimuli. Not
      revealing the sham-injection condition will allow for comparison between nociceptive
      (injection) and non-nociceptive (sham-injection) condition.

      Because no previous studies have investigated tactile acuity changes in acute low back pain,
      the sample size calculation was based on the data from our own systematic review and
      meta-analysis (Adamczyk et al., under review) and previous cross-sectional data among healthy
      controls (Adamczyk et al., 2016). Based on reported mean difference of 9.49mm between chronic
      low back pain patients and healthy controls and standard deviation of 9.90mm, a total sample
      size of 57 participants (19 per group) is required to detect a significant effect. Power
      calculation was performed for specific planned-comparison tests that were described in
      detailed under 'statistical analysis' section below. Calculation was performed in G*Power
      (G*Power 3.1.9.2 statistical software) with the alpha level set at =0.05 and 80% power.

      Baseline differences in descriptive statistics will be analysed by one-way analysis of
      variance (ANOVA) with 'group' as the between-subject factor. Further statistical comparisons
      will be performed using a repeated-measures ANOVA design, with 'group' (real-injection,
      sham-injection, and control group) as between-subject factor and repeated measures
      (assessment 1, 2 and 3) as a within-subject factor. In order to test hypothesis on tactile
      acuity alteration during pain induction, F-tests will be followed by planned comparisons on
      data from assessment 1 versus assessment 2 in experimental group. To determine whether the
      magnitude of tactile acuity alteration has differed between the groups, planned comparisons
      will be performed on the difference in tactile acuity (assessment 1 vs. assessment 2) between
      real-injection and sham-injection group and between real-injection and control group.
      Bonferroni correction will be used for multiple planned comparisons. Forward, stepwise
      multiple regression will be performed to determine the degree to which tactile acuity change
      is predicted by either pain intensity or the size of its distribution. All the analyses will
      be conducted using the STATISTICA data analysis software, version 12 (StatSoft Inc., Tulsa,
      OK, USA). The level of significance will be set at p < 0.05.
    

Intervention name(s): Saline injection; Sham injection
Intervention type(s): Other; Other
Intervention description(s): In the saline injection group, low back pain will be induced via 1.0 ml hypertonic (5% NaCl) saline bolus injection which is a commonly used model of acute low back pain. Saline will be injected into the right (or left) lumbar longissimus muscle 50 mm lateral to the spinous process just above (5 mm) previously marked point. Injections will be performed by a physician under ultrasound imaging guidance to ensure that each single injection will be equally placed at a depth of 30 mm. The side for the pain induction will be randomised across subjects. The place of needle insertion and corresponding point on the opposite side of the body will be covered by placing a small piece of adhesive plaster.; In the sham-injection group (placebo comparator), a real needle will be shown to the participants to imitate and produce the anticipation of a pain experience. A pinprick sensation will be produced by a weighted stimulus applied perpendicularly to the skin just above without piercing the skin. A stimulus of 512 mN will be used to produce a pinprick sensation and activation of cutaneous nociceptors. Adhesive tapes covering stimulation points will also be provided.
Other intervention name(s): Experimental pain; Sham pain
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: Tactile acuity; Chronic pain; Two-point discrimination; Point-to-point test; Two-point estimation; Body image