Experimental neck muscle pain increase pressure pain threshold over cervical facet joints.

Aims Evaluate pressure pain threshold (PPT) over cervical facet joints before and after injection of experimental pain in the trapezius and multifidus muscles. Methods Fourteen healthy subjects (6 women) received randomized ultrasound-guided injections of hypertonic saline (5.8%), in the right multifidus muscle medial to C4/C5 facet joint and in the right trapezius muscle at the midpoint between C7 spinous process and acromion. The saline-induced pain intensity was assessed on a VAS scale. Before and during saline-induced pain PPTs were assessed by pressure algometry bilaterally over C2/C3 and C5/C6 facet joints. Three-way repeated-measures ANOVA with factors PPT location, injection site, and time was used for analysis. Post-hoc analysis was done by Bonferroni. Results Saline-induced trapezius muscle pain increased PPTs over all facet joints (P < 0.05) compared with before pain. Saline-induced multifidus muscle pain increased PPTs bilaterally over C2/C3 facet joints and over the left C5/C6 facet joint (P < 0.05) compared with before pain. Conclusions Trapezius muscle pain increased PPT over assessed facet joints. Similar results were found for multifidus muscle pain except for the right C5/C6 facet joint, which was close to the injection site. Such findings may reflect descending inhibitory control acting on structures furthest away from the painful structure.