## 4 Local Anesthetics  
(1) Periarticular injection  
Local infiltration analgesia (LIA) is based on the injection of an anesthetic cocktail into periarticular regions (multiple punctures into posterior capsule, collateral ligaments, capsular incision, quadriceps tendon, and subcutaneous tissues), near the end of a surgical procedure, with the aim to prevent generation and conduction of pain signals from incision. LIA significantly reduces pain scores and opioid consumption and improves functional outcomes and range of motion in the early postoperative period after TKA [23; 24; 25; 26]. Single femoral nerve block and LIA provide equally satisfying analgesia, but the well-known risk of motor blockade with block may render this method less attractive [26; 27]. The composition of LIA includes a combination of local anesthetic (ropivacaine 150-400 mg or bupivacaine 20-400 mg), ketorolac (15-30 mg), morphine (4-10 mg), clonidine (80 mg), corticosteroid (methylprednisolone 40 mg or betamethasone 1-4 mg), and epinephrine (300-600 mg). However, the combination of medications is heterogeneous and varies according to the surgeon's habits. The lack of comparative studies makes it difficult to define the most effective analgesic dosages. The use of LIA with liposomal bupivacaine does not appear to improve the duration of pain control in patients undergoing TKA. If periarticular injection is performed in addition to peripheral nerve blockade, the total dose of LIA should be calculated to avoid excessive dosing and to minimize the risk of local and systemic anesthetic toxicity [28; 29; 30]. (2) Neuraxial anesthesia  
Epidural analgesia was used as a postoperative analgesic regimen for patients after TKA, consisting of a local anesthetic agent and an opioid. Compared with parenteral opioids, epidural analgesia provides better postoperative analgesia with less nausea, vomiting, and pruritus [31]. However, some studies show that epidural anesthesia has many adverse effects, such as urinary retention, hypotension, pruritus, and motor blockade, which preclude rapid functional recovery [32; 33]. Epidural analgesia provides no additional analgesic benefit when compared with peripheral nerve blocks or LIA. Continuous epidural analgesia may be added to a multimodal analgesic regimen for patients who undergo complex TKA or are expected to have difficulty with pain control. Intrathecal morphine injection reduces postoperative pain significantly early (first 12 to 24 h), but does not seem to provide superior control of pain to LIA. It is easier to perform and less time-consuming than the regional blocks. The side effects (such as epidural analgesia) could interfere with postoperative recovery, therefore this technique is indicated when TKA surgery is performed under spinal anesthesia and neither peripheral nerve blocks nor LIA is possible [34; 35]. (3) Peripheral nerve blocks  
The use of peripheral nerve blocks (PNBs) is a common practice in orthopedic surgery, but it is limited by availability of a trained regional anesthesia team. PNBs provide excellent pain management after TKA, promote early mobilization, and reduce the consumption of opioids, the incidence of opioid-related adverse effects, and the hospital stay [36; 37]. Femoral nerve blocks (FNBs) have been widely accepted as the gold standard for TKA postoperative pain relief. Although FNBs may provide effective analgesia (antero-medial part of the knee, leaving the posterior knee untargeted), they reduce the muscle strength postoperatively, increasing the risk of falling. Adductor canal blocks (ACBs) reduce the same pain scores as FNBs (anteroomedial part of the knee, leaving the lateral and posterior compartments uncovered), but preserve quadriceps strength, thus preventing falls and facilitating early mobilization in patients after TKA. A single-shot ACB results in a better early rehabilitation, a longer ambulatory distance, and a reduction in length of hospital stay compared with FNB. Continuous catheter ACBs are not recommended because of inconsistent benefits [19].