Table 9

Randomized studies evaluating a placebo response rate using saline control injections

StudyNumber of patientsStudy designType of blocks (placebo arm)Placebo response or false-positive rate*Comments
Revel et al 45 80–38 who received placeboRandomized, parallel groupIA with 1 mL saline18% placebo responseResponse defined as >75% relief.
Cohen et al 18 229–47 who received placeboRandomized, three-arm parallel groupMBB with 0.5 mL saline30% placebo responseResponse defined as >50% relief.
Lord et al 209 50 patients with whiplashRandomized, three-period crossoverCervical MBB with 0.5 mL bupivacaine, lidocaine and saline40% placebo response, false-positive rate (concordant relief with LA blocks but positive response to placebo) 19%Response defined as longer pain relief (complete or profound) with bupivacaine than lidocaine, and a negative response to saline. False-negative rate (positive but discordant response to LA injections but negative response to placebo) 32%. Sensitivity 54%, specificity 88%.
Dias da Rocha et al 173 104Patient-blinded, one-way crossoverLumbar MBB with 0.5 mL saline, and if negative, lidocaine16% placebo responseResponse defined as ≥50% relief. All patients received saline and if negative, lidocaine MBB after 10 min.
Schütz et al 146 60Single-blind, three-way crossoverBilateral lumbar IA injections with 1.5 mL of mepivacaine (verum), saline (placebo) or extra-articular needle placement without injection (sham)Sham and placebo groups had 20% and 38% response rates, respectively, at 1 hourResponse defined as >2-point decrease in back pain. Non-inferiority shown between placebo and verum injection.
  • Injections in lumbar spine unless specified.

  • *False-positive rate based on positive response to verum and negative response to sham injection.

  • IA, intra-articular; LA, local anesthetic; MBB, medial branch block.