OBJECTIVES: Pain relief is a strong predictor of patient satisfaction after total knee arthroplasty (TKA). Despite the limitations in self-reported measures, specific pain performance assessments may provide health providers a more distinct impression of pain among TKA population. This study aims to establish the average pattern of self-reported-face-rating pain score using linear mixed modeling and to explore pre-operative predictors of post-operative pain following primary TKA.

METHODS: Through data partnership with Mercy-Technology-Services, the IT arm of St. Louis-based Mercy health system, patients who underwent TKA surgery were extracted from 2011-2018 Mercy electronic health records, which is one of the most comprehensive real-world databases including preoperative and intraoperative information. Around 1,368, 956, 1,529, 1,141, and 1,152 out of 24,830 TKA patients were with both baseline and follow-up pain score at 2-week, 1-month, 3-months, 6-months and 12-months after surgery, respectively. Average pain relief curve was characterized using linear mixed regression modeling. Predictors associated with no-pain-relief (no-change/increased pain score) three-months after surgery were investigated using machine learning algorithms. The model accuracy was measured by area under the curve (AUC).

RESULTS: Although patients started with different levels of pain score, similar pain relief patterns were observed (age-mean 67y (SD: 10); 63% female; 45% Medicare). The study population started with an average pain score of 6.4 and changed by -0.2 per month. Both intercept and slope of time were statistically significant. Around 64.4% patients reported pain relief three-months after surgery. Predictive preoperative variables for no-pain-relief were lower provider’s TKA surgery volume, lower baseline pain level, female, current smoking and illicit drug use. The test and training data resulted in similar AUC (test: 0.75, training:0.72).

CONCLUSIONS: Over 60% of the study TKA population reported pain relief three months after surgery. Controlling baseline pain score and social behavior intervention before surgery may increase the chance of pain relief after TKA surgery.