Fifteen RCTs were included in the review. Four trials had good external validity and 11 trials had moderate external validity. For internal validity, two trials were rated good, 11 were rated moderate and two were rated poor. No relevant systematic reviews were identified.
Head, neck, shoulder and back pain (10 RCTs, 439 patients): Five RCTs evaluated trigger point injections with local anaesthetic. One RCT showed lidocaine trigger point injection was more effective in relieving myofascial pain up to one week than either SPGB or placebo SPGB. A second RCT found similar reductions in pain scores for prilocaine trigger point injections and tropisetron trigger point injections after seven days, but greater pain relief in the tropisetron group at eight weeks. A third RCT found adding lidocaine trigger point injections to neck stretching improved pain symptoms more than adding ultrasound at two weeks and three months. A fourth RCT found no detectable difference at six months between adding prilocaine trigger point injections or laser treatment to stretching exercises. A fifth RCT reported significant benefits of lidocaine trigger point injections over dry needling in terms of pain, fatigue and work disability four weeks after treatment.
Six RCTs evaluated trigger point injections with botulinum toxin. Three RCTs reported saline trigger point injections and botulinum type A trigger point injections to be equally effective in reducing pain and disability at four months and one reported equivocal results. One trial reported no differences between botulinum toxin trigger point injections and bupivicaine trigger point injections. One RCT reported similar findings for botulinum toxin trigger point injections and lidocaine trigger point injections when added to stretching exercises.
Whiplash syndrome (two RCTs, 66 patients): One RCT reported a significant improvement in whiplash syndrome symptoms at three months and in pain scores and mobility at eight months for sterile water trigger point injections compared to saline trigger point injections. A second RCT reported no difference between botulinum toxin trigger point injections and saline trigger point injections in terms of pain, function or range of motion at four weeks.
Craniofacial pain (one RCT, 30 patients): One RCT reported that procaine trigger point injections combined with simulated dry needling offered little beyond a placebo effect.
Cervicogenic headache (one RCT, 33 patients): One RCT reported no differences between the addition of botulinum toxin trigger point injections or saline trigger point injections to physical therapy.
Knee osteoarthritis (one RCT, 33 patients): One RCT reported significant benefits in terms of pain and knee function for addition of lidocaine trigger point injections to intra-articular injection in selected older patients.
Very few adverse events were reported among the included RCTs of trigger point injections.