Evaluating the Association between Acute and Chronic Pain after Surgery: Impact of Pain Measurement Methods

There is a need to predict chronic (≥3▒mo) postsurgical pain (CPSP). Acute (<7▒d) pain is a predictor, i.e. more severe pain associated with higher CPSP risk. However, reported associations vary widely. Using a systematic search, we examined associations between two acute pain measures (pain at rest [PAR] and movement-evoked pain [MEP]) and CPSP outcomes (considering severity vs. any "non-zero" pain only) in 22 studies. Seven studies reported the relationship between CPSP and both PAR and MEP. Of these, 2/7 reported no association, 3/7 reported significant associations for both PAR and MEP, 1/7 reported an association for PAR only and 1/7 reported an association for MEP only. Six of another 7 studies reporting only the association for MEP found a significant relationship. Three of the 5 studies that did not specify whether acute pain outcomes were PAR or MEP reported a significant relationship. Another 3 studies reporting a relationship with CPSP did not specify whether this was for PAR, MEP or both. All investigations incorporating severity of CPSP in their analyses (n=7) demonstrated a significant relationship, whereas only 10 of the 15 studies that dichotomized CPSP outcome as "no pain" versus "any"/"non-zero pain" were positive. Overall, evidence for an association between acute and chronic pain is moderate at best. However, closer attention to pain measurement methods will clarify the relationships between acute pain and CPSP. We propose that future CPSP predictor studies assess both PAR and MEP acutely and also incorporate CPSP severity in their analyses.