Pain after total knee arthroplasty (TKA) is usually severe. It causes a state of discomfort that may directly influence patients' functional recovery. The pain involved has specific characteristics: a 55 to 60% incidence at rest and up to70% upon mobilization; high or very high intensity; and pain peaking at 3 to 6 hours after surgery and continuing for the following 72 hours [1, 2]. Anesthetic techniques such as epidural analgesia or peripheral nerve block may reach effective analgesic levels [3–5] in combination with opioid analgesics and non-steroidal anti-inflammatory drugs. Both techniques either have significant demands on technical skills, have potential side effects, or are costly [6–8]. Recently, local anesthesia techniques have become popular, including: (1) periarticular infiltration with or without local intermittent administration of anesthetics with an intra-articular catheter [6, 7, 9–12]; and (2) a combined technique with infiltration plus continuous infusion [8, 13, 14]. Local anesthesia has shown several advantages (less intensity of postoperative pain, less consumption of rescue analgesics and earlier discharge) when compared to other regional or purely systemic approaches [15–17].
There is some controversy surrounding periarticular infiltration anesthesia. Some studies, using single-dose or combined-dose periarticular infiltration, have shown transient effects, “rebound pain”, or no effectiveness in pain control [12, 18–21]. The continuous intra-articular infusion technique has been introduced to improve these transient effects. Two previous studies [8, 14] using continuous intra-articular infusion anesthesia showed better pain relief and less opioid use than a control group using saline infusion. Further investigation is needed to assess the efficacy of continuous intra-articular infusion anesthesia. One of the most concerning issues is whether continuous intra-articular infusion would increase the risk of early periprosthetic joint infection (PJI). Early diagnosis of PJI is challenging; at the present time, diagnosis of PJI remains dependent on clinical judgment and reliance on standard clinical tests including serologic tests, analysis of aspirated joint fluid, and interpretation of intraoperative tissue and fluid test results.
For this purpose, the aims of our study were: (1) to analyze the efficacy of continuous intra-articular infusion anesthesia in postoperative pain control and functional recovery compared with epidural analgesia; and (2) to investigate PJI markers, such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), synovial fluid cell count and culture during follow-up, to determine whether the risk of early PJI increases with a continuous intra-articular infusion procedure.