Abstract
Objective
There is limited information about the extent to which the association between pre-operative and chronic post-operative pain is mediated via pain-on-movement or pain-at-rest. We explored these associations in patients undergoing total hip (THR) and total knee (TKR) replacement.
Methods
322 and 316 patients receiving THR and TKR respectively were recruited into in a single centre UK cohort (APEX) study. Pre-operative, acute post-operative and 12-month pain severity was measured using self-reported pain instruments. The association between pre-operative / acute pain and chronic post-operative pain was investigated using structural equation modelling (SEM).
Results
Patients with high levels of pre-operative pain were more likely to report chronic pain after THR (β=0.195; p=0.02) and TKR (β=0.759; p<0.0001). Acute post-operative pain-on-movement was not associated with chronic pain after TKR or THR after adjusting for pre-operative pain, however acute pain-at-rest was associated with chronic pain after THR (β=0.20; p<0.0002) but not TKR after adjusting for pre-operative pain. Analysis of pain-at-rest and pain-on-movement highlighted differences between THR and TKR patients. Chronic pain after THR was weakly associated with pain-at-rest during the pre-operative (β=0.11; p=0.068) and acute post-operative period (β=0.21; p<0.0001). In contrast, chronic-pain after TKR was strongly associated with the severity of pain-on-movement during the pre-operative period (β=0.51; p=0.001).
Conclusions
SEM illustrated the different patterns of association between measures of pain over time in patients undergoing THR and TKR for osteoarthritis. These findings highlight the importance of future work which explore the mechanisms underlying pain-on-movement and pain-at-rest.
Level of Evidence
2
Approvals
The APEX trials were registered as an International Standardised Randomised Controlled Trial (96095682), approved by Southampton and South West Hampshire Research Ethics Committee(09/H0504/94) and all participants provided informed written consent.
