Arthroscopic knee surgery is commonly performed as an outpatient procedure and is often associated with postoperative pain. Intraarticular (IA) local anesthetics (LA) are often used for prevention of pain after arthroscopic knee surgery; however, the degree of postoperative pain varies. In an effort to find the ideal regime for sufficient, long-lasting postoperative analgesia, many different drugs, including opioids, nonsteroidal anti-inflammatory drugs, ketamine, clonidine, and neostigmine, have been added to the IA LAs The investigators designed this study to compare the efficacy of intra-articular administration of neostigmine versus ketamine as adjuvant analgesics after knee arthroscopy.