​Even though a total knee replacement is an effective surgical treatment for end-stage knee osteoarthritis and the majority of patients report significant pain relief and functional improvement post-surgical, literature shows that up to 20% of patients undergoing a total knee replacement are dissatisfied and complain of persisting pain, functional disability and poor QoL ( Scott et al. 2010). 

Given the significant role of altered central pain modulation in a subgroup of patients with knee osteoarthritis (Lluch et al. 2013), it is not surprising that surgical interventions such as total knee replacements do not guarantee complete pain reduction or functional recovery. This underscores the need for a better understanding of the role of altered central pain modulation in predicting outcome after a total knee replacement. 
We aimed to systematically review whether the presence of altered central pain modulation pre-surgical influences outcome after a total knee replacement in patients with knee osteoarthritis, and if so which indices of central pain modulation predict poor outcome (Baert et al. 2015).

Most important results

• Strong evidence is available that presence of catastrophic thinking and poor coping strategies predict more pain after a total knee replacement and that there is no association between fear of movement and post-surgical pain or function. 
• Evidence on other psychosocial influences is limited or conflicting.
• Literature on the influence of other signs of altered central pain modulation is scarce. It is plausible that signs as joint pain at rest or widespread pain sensitization predict more post-surgical pain.

Conclusion 
As the economic impact of severe, unexplained pain after a total knee replacement is profound, surgeons should be attentive for patients with signs of altered central pain modulation before surgery as they might be at risk for unfavorable outcome after a total knee replacement. A broader therapeutic approach aiming to desensitize the central nervous system can be adapted in these patients. However, further research is needed to identify the role of central pain modulation in predicting outcome after a total knee replacement and to address questions concerning the effectiveness of interventions that target different aspects such as the central nervous system, in contrast to therapeutic modalities only directed to structural knee joint pathology. 

Isabel Baert 

2015 Pain in Motion

References and further reading: 

Baert IAC, et al., Does pre-surgical central modulation of pain influence outcome after total knee replacement? A systematic review, Osteoarthritis and Cartilage (2015) http://www.ncbi.nlm.nih.gov/pubmed/26382109