Validation of an index of Sensitivity to Movement-Evoked Pain in patients with whiplash injuries.

Sensitivity to Movement-Evoked Pain is a pain summation phenomenon identified in various chronic pain populations. This study investigated the validity of a procedure used to assess pain summation in response to a repeated lifting task in individuals with whiplash injuries. Sixty-five participants completed measures of pain severity and duration, Temporal Summation (TS) of pinprick pain, pain catastrophizing and fear of movement, and work-related disability before lifting a series of 18 weighted canisters. An index of Sensitivity to Movement-Evoked Pain was computed as the increase in pain reported by participants over successive lifts of the weighted canisters. An index of TS was computed by dividing the pain reported in response to the final pinprick by the pain reported in response to the 1st pinprick in a train of 10 pinpricks. Analyses replicated previous findings showing a repetitive lifting task-induced pain summation in approximately 20% to 25% of a sample of individuals with whiplash injuries. Analyses also revealed significant correlations between SMEP, TS, and pain-related psychological variables. Hierarchical regression analyses showed that TS and pain catastrophizing made significant unique contributions to the prediction of SMEP. These findings join a growing body of research on movement-evoked pain in persistent spinal pain conditions. The repeated lifting task used in this study successfully induced pain summation in a group of patients with whiplash injuries.