The Association Between Pre-operative Pain Psychology and Hypersensitivity With Poor Functional Outcome After Knee Replacement

Knee osteoarthritis (OA) is a major cause of disability around the world; it is the most common chronic condition in primary care in the UK. By 2030 it is predicted to be the greatest cause of disability in the general population. An effective end-stage treatment for knee OA is knee-replacement surgery, which was first done in the 1970s and 1980s.

In England and Wales, the number of knee-replacement procedures recorded by the National Joint Registry in 2013 was 91,703, which represents an increase of 0.9 % over 2012. The data analysis by the National Joint Registry and the Office of National Statistics suggests that, by 2030, primary TKAs will increase by 117% from the 2012 level. Subsequently, TKA revision surgeries are expected to increase incrementally by 332%. There is a similar estimation of demand for revision TKA surgeries in the United States; by 2030, they are expected to rise by 601% from the 2005 level. The United States estimation of primary TKA is for growth of 673% from the 2005 level, which is similar to England and Wales's upper-limit projections.

Post-TKA, 75-85% of patients report satisfaction with surgery outcomes, while the remaining 15-25% are dissatisfied . Total knee arthroplasty's success has traditionally been evaluated from the surgeon's perspective, e.g. the presence of surgical complications or implant survival. This is gradually changing to involve the patient in measuring health outcomes and decision-making processes. Patient-reported outcome measures (PROMs) have evolved to explore patient perspectives by monitoring the quality of care in health organizations and conducting clinical trial outcomes.

Worldwide National Joint Registry summarise the common indication for TKA revision are; 29.8% due to aseptic loosening, 14.8% infection and 9.5% due to pain. Most prediction studies show that pain and psychology pre-operation may predict poor outcomes post-TKA. A systematic review by concludes that pain catastrophizing predicts chronic pain post-TKA. Pain catastrophizing is defined as a construct that reflects anxious preoccupation with pain, an inability to inhibit pain-related fears, amplification of the significance of pain vis-à-vis health implications, and a sense of helplessness regarding pain.

Chronic post-surgery pain is significantly associated with preoperational central sensitisation as in post-shoulder subacrominal decompression and hernia repair. Regarding post-TKA, a study by Lundblad et al. (2008) concluded that the preoperational hand electrical pain threshold significantly predicts pain outcomes one year post-TKA. The study explored the association between chronic pain post-TKA and preoperation widespread pain sensitisation using pressure algometry. Both study association without control the psychological confiding factor. The correlation with Western Ontario and McMaster Universities Osteoarthritis Index pain score (WOMAC) is questionable due to weakness of WOMAC with post TKA population such as low sensitivity of WOMAC's stiffness subscale reduces the overall standardized response mean and high ceiling effect Psychological pain thinking is assessed using the most widely used measuring scale: Pain Catastrophizing Scale (PCS). PCS assesses pain thinking in three dimensions: rumination ("I can't stop thinking about how much it hurts"), magnification ("I worry that something serious may happen") and helplessness ("It's awful and I feel that it overwhelms me").