Systematic review of movement-evoked pain versus pain at rest in postsurgical clinical trials and meta-analyses: a fundamental distinction requiring standardized measurement.

To estimate frequency of movement-evoked pain (MEP) measurement in human postsurgical investigations, we reviewed thoracotomy, knee arthroplasty, and hysterectomy clinical trials and meta-analyses. Only 39% of trials measured MEP and 52% failed to identify pain outcome as pain at rest (PAR) or MEP. Temporal trending did not suggest that MEP measurement is becoming more frequent. Trials measuring both MEP and PAR suggest that MEP is 95-226% more intense than PAR in the first 3 postoperative days. Among trials measuring MEP, 38% did not specify the physical maneuver used to assess MEP. Five of 7 meta-analyses reviewed (71%) did not distinguish between PAR and MEP, and none of the 7 meta-analyses declared the 20-59% of reviewed trials that had failed to identify their pain outcome as PAR or MEP. These results suggest an unchanging neglect of MEP in postsurgical pain trials and frequent failure to identify pain outcome as PAR or MEP. This is an important problem because MEP is usually more severe than PAR; MEP exerts a more direct adverse impact on postsurgical functional recovery and several current and novel pain treatments differentially affect MEP vs PAR. Failure to distinguish between PAR and MEP and standardize their measurement threatens trial precision and ability to identify interventions with the most clinically relevant effects on pain. We therefore recommend developing consistent terminology regarding PAR and MEP, considering inclusion of MEP as a pain outcome in every postsurgical trial, and standardizing measurement of PAR and MEP on a procedure-specific basis.