Is inpatient rehabilitation a predictor of a lower incidence of persistent knee pain 3-months following total knee replacement? A retrospective, observational study

BACKGROUND: Moderate to severe levels of persistent knee pain have been estimated to affect up to 25% of people 3-months or more after a total knee replacement. It is unknown whether the type of rehabilitation pathway is associated with persistent high pain after surgery. Using a prospectively followed Australian cohort who underwent total knee replacement for knee osteoarthritis, this study aimed to i) report the incidence of high-intensity knee pain (defined as a score ≤ 15 on the Oxford Knee Score pain subscale) across time and ii) identify whether referral to inpatient rehabilitation was one of the predictors of persistent pain at 3-months post-surgery. METHODS: A retrospective analysis of a large prospective study was conducted using the Oxford Knee Score pain subscale to determine if participants had high pain at 3-months, 12-months and 36-months post-surgery. Relative risks for high pain at 3-, 12- and 36-months between the type of rehabilitation pathway were determined using Poisson multivariable regression with robust standard errors. The same technique was also employed to determine potential predictors, including rehabilitation pathway, of high pain at 3 months. RESULTS: The incidence of high pain in all participants was 73% pre-surgery and 10, 5 and 6% at 3-, 12- and 36-months respectively following knee replacement. There was a significant interaction between time and rehabilitation pathway, suggesting that the effect of the rehabilitation pathway varied across time. The incidence of high pain at 3-months did not significantly differ between those who attended inpatient rehabilitation (11.6%) and those discharged directly home (9.5%). Multivariable Poisson regression analysis identified the pre-surgical presence of high pain, co-morbid low back pain or other lower limb problem, younger age and having a major complication within 3-months following surgery as significant predictors of persistent pain whilst discharge to inpatient rehabilitation was not. CONCLUSION: A small but clinically significant minority of people continued to have high pain levels at 3-, 12- and 36-months following a primary total knee replacement for osteoarthritis. Participation in an inpatient rehabilitation program does not appear to be an important predictor of ongoing knee pain. TRIAL REGISTRATION: The data were collected in the Evidence-based Processes and Outcomes of Care (EPOC) study, ClinicalTrials.gov Identifier: NCT01899443.