Association of preoperative pain in knee and external to knee with postoperative pain outcome after total knee arthroplasty

BACKGROUND: Preoperative pain in the symptomatic knee may predict postoperative pain severity in patients undergoing total knee arthroplasty (TKA). However, the effect of preoperative pain external to the knee on postoperative pain is unclear. This study evaluated postoperative pain outcomes in TKA patients according to the presence of preoperative pain in the knee only or in the knee and external to the knee. METHODS: We retrospectively assessed medical records of patients who underwent unilateral TKA. The relationship between reported preoperative pain characteristics and morphine equivalent consumption or numerical rating scale (NRS) pain scores on postoperative day (POD) 0–3 was assessed using a multivariable generalized linear model. RESULTS: In total, 3,429 adult patients who underwent their first TKA were included; 2,864 (83.5%) patients preoperatively experienced only knee pain and 565 (16.5%) knee pain with external to knee pain. Preoperative pain in the knee and external to the knee was associated with 5% higher morphine equivalent consumption on POD 0–3 compared to preoperative knee pain only (exponentiated regression coefficient: 1.05; 95% confidence interval: 1.02 to 1.09; P = 0.004). However, the NRS pain scores on POD 0, 1, 2, and 3 and adjuvant analgesics consumption (acetaminophen and ketorolac) on POD 0–3 were not significantly different between the two groups (P > 0.05). CONCLUSIONS: This study showed that there was an increase of morphine equivalent consumption during POD 0–3 in patients with preoperative knee pain with external to knee pain than in patients with preoperative only knee pain.