Soft Tissue Stiffness Before and after Trigger Point Injections in Neck–Shoulder Myofascial Pain Syndrome: A Double-Blind, Randomized, and Controlled Crossover Trial with Botulinum Toxin A and Saline Injections

ABSTRACT

Objectives: To determine values of soft tissue stiffness [STS] before and after injection treatment in neck–shoulder myofascial pain and to correlate them with self-reported and clinically assessed pain and disability.

Methods: Thirty-one patients recruited by newspaper advertisement were screened by a physician. The subjects received either botulinum toxin A [BTA] or saline injections on two occasions four weeks apart. The volume of each injection was 0.05 ml of either normal saline [without preservative] or saline containing five units of BTA. The total dose varied from 15 to 35 U of BTA [total volume 0.15 to 0.35 ml]. The follow-up measurements were performed at four weeks after each treatment. The STS of trigger points [TrPs] and a reference point was determined using the STS meter [STSM]. The pressure-pain threshold [PPT] was determined using the dolorimeter. The subjective severity of neck–shoulder pain [SSNP] and the neck pain and disability scale [NPDS] were assessed with questionnaires. The active and passive range of motion [ROM] of cervical spine was determined.

Results: The mean STS of all TrPs showed a slight but statistically significant decline during the whole study period [P = 0.040], but there were no statistically significant changes in the individual STS values of TrPs after the injections although pain [measured by SSNP, NPDS, and PPT] was reduced. The STS values differed significantly [P < 0.001] depending on the site of measurement. There was no clear consistent correlation between STS and SSNP, NPDS, PPT or ROM measurements.

Conclusions: The STS of single neck muscles is not changed after injections of physiological saline or small doses of BTA. There is no clear consistent correlation between STS and self-reported or clinically assessed pain and disability.

KEYWORDS. :

• Neck muscles
• myofascial pain syndrome
• botulinum toxin type A
• tissue stiffness
• trigger point injection
• dolorimeter

ACKNOWLEDGEMENTS

The authors would like to thank Pirjo Halonen, PhD, for her technical assistance. This study has been supported by an EVO grant [5041705] from Kuopio University Hospital.

Declaration of interest: The author reports no conflict of interest. The author alone is responsible for the content and writing of this paper.