Head repositioning accuracy is influenced by experimental neck pain in those most accurate but not when adding a cognitive task.

Background and aims Neck pain can impair perception of cervical movement, but how this is affected by attention is unknown. In this study, the effects of experimental neck pain on head repositioning accuracy during standardized head movements were investigated. Methods Experimental neck pain was induced by injecting hypertonic saline into the right splenius capitis muscle in 28 healthy participants (12 women). Isotonic saline was used as control. Participants were blindfolded while performing standardized head movements from neutral (start) to either right-rotation, left-rotation, flexion or extension, then back to neutral (end). Movements were triplicated for each direction, separated by 5-s, and performed with or without a cognitive task at baseline, immediately after the injection, and 5-min after pain disappeared. Repositioning accuracy was assessed by 3-dimensional recordings of head movement and defined as the difference between start and end position. Participants were grouped into most/least accurate based on a median split of head repositioning accuracy for each movement direction at baseline without the cognitive task. Results The most accurate group got less accurate following hypertonic injection during right-rotation without a cognitive task, compared with the least accurate group and the isotonic condition (p < 0.01). No group difference was found when testing head repositioning accuracy while the participants where distracted by the cognitive task. Conclusions Experimental neck pain alters head repositioning accuracy in healthy participants, but only in those who are most accurate at baseline. Interestingly, this impairment was no longer present when a cognitive task was added to the head repositioning accuracy test. Implications The results adds to our understanding of what factor may influence the head repositioning accuracy test when used in clinical practice and thereby how the results should be interpreted.

Light Touch Contact Improves Pain-Evoked Postural Instability During Quiet Standing.

Objective: To investigate if attention to additional sensory information from the fingertip can improve postural stability during pain, which is known to impair balance. Methods: In 16 healthy volunteers, experimental pain was induced by intramuscular injection of hypertonic saline in the right vastus medialis muscle (isotonic saline used as nonpainful control, intramuscular injection in the same location). Pain intensity was assessed on an 11-point numeric rating scale (NRS; 0 representing "no pain" and 10 "maximum pain"). Subjects were asked to stand as still as possible on a force plate for 40 seconds with their eyes closed. Their postural stability was quantified by the area and velocity of center of pressure (CoP) displacement. The CoP was recorded with and without pain during two different conditions: 1) no touch and 2) the subjects were asked to lightly touch a curtain with their right index finger and focus their attention on keeping it as still as possible. Results: Hypertonic injections induced higher NRS scores compared with control injections (P < 0.05). During the hypertonic injection condition, the CoP area and velocity in both directions increased during no touch compared with the light touch condition (P < 0.05). No differences were found during light touch between the hypertonic and isotonic injection conditions. Although experimental knee-related pain impaired postural stability, lightly touching a curtain with the fingertip decreased postural sway during painful conditions. Conclusions: Providing additional sensory information while pain patients are performing balance exercises may improve postural stability and increase the quality of exercise, consequent rehabilitation protocols, and clinical outcomes.