Papers of the Week

Shoulder surgery is a primary intervention for shoulder pain, yet many individuals experience persistent post-operative pain. Previously, we found individuals categorized as having a high-risk phenotype (comprised of COMT variation and pain catastrophizing) had approximately double the chance of not reaching a 12-month pain recovery criterion. As a means to better understand the development of persistent post-operative shoulder pain, this study advanced our previous work by examining temporal ordering of post-operative shoulder recovery based on potential mediating factors, and expansion of outcomes to include movement-evoked pain and shoulder active range of motion. Before surgery, individuals were categorized as either high-risk (high pain catastrophizing, COMT-genotype linked to low enzyme activity (n=41)) or low-risk (low pain catastrophizing, COMT-genotype linked to normal enzyme activity (n=107)). We then compared potential mediating variables at 3, 6, and 12 months post-operatively: 1) endogenous pain modulation defined by a conditioned pain modulation paradigm (CPM); and 2) and emotion factors such as anxiety, fear of movement, and depressive symptoms. At 3 months, the high-risk subgroup had higher fear and movement-evoked pain, and causal mediation analysis confirmed the direct effect of risk subgroup on 12-month movement evoked pain. However, 12-month depressive symptoms were found to mediate 53% of the total effect of risk subgroup on 12-month movement-evoked pain. This study introduces potential temporal components and relationships to the development of persistent post-operative shoulder pain, which future studies will confirm and assess for potential therapeutic targets. Perspective: This study expands upon post-operative shoulder recovery measures to include movement-evoked pain and depressive symptoms, and provides preliminary indication of temporal ordering to post-operative shoulder recovery for a pre-identified high-risk subgroup. Future studies will distinguish temporal components of shoulder surgery that may optimize treatment targets of post-operative recovery.