This study was designed to investigate the effect of hot pack or cold pack application on the soreness after injection into a myofascial trigger point of the upper trapezius muscle in 45 patients.

All patients were injected on the trigger points and divided into 3 groups: hot pack, cold pack and control groups. Hot and cold packs were applied in each 15 patients of hot and cold pack groups, respectively for 20 minutes after trigger points injection, and no pack was applied in 15 patients of control group.

A degree of improvement of postinjection soreness was assessed by the subjective pain intensity(visual analogue scale; VAS) and the pressure pain threshold of trigger point using pressure algometer. The VAS was assessed 20 minutes, 24 hours, 48 hours, and 72 hours after trigger point injection with hot pack or cold pack application. The pressure pain threshold was assessed before injection, immediately, 20 minutes, and 3 to 7 days after injection with hot pack or cold pack application.

Significant improvement of pressure pain threshold was observed at 3 to 7 days after injection in the hot pack group. On the other hand, the VAS was significantly decreased at 20 minutes, 48 hours, and 72 hours after injection in the hot pack group.

Therefore, hot pack application after injection is helpful to decrease the post injection soreness.