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Synopsis: Preemptive analgesia and postoperative multimodal analgesic techniques should be used to minimize pain for patients undergoing arthroscopic surgery of the knee.
Source: Reuben SS, Sklar J. Pain management in patients who undergo outpatient arthroscopic surgery of the knee. J Bone Joint Surg Am 2000;82-A:1754-1766.
Although arthroscopic knee surgery is a commonly performed procedure, perioperative pain management varies widely among surgeons. Many surgeons still perform anterior cruciate ligament (ACL) reconstruction with an inpatient hospital stay. Advances in perioperative analgesia techniques allow this procedure now to be done as an outpatient routinely and also help to minimize pain in all patients undergoing arthroscopic knee surgery. Strategies to help minimize pain in the safest and most efficient manner are outlined in a recent "Current Concepts Review" by Sklar and Reuben.
Many factors contribute to pain following arthroscopic knee surgery, including surgical trauma with direct input to the central nervous system (CNS). Prolonged inflammation can contribute to hypersensitivity of the nerve endings in the area and subsequent reduction in the threshold of the afferent nerve terminals. Central sensitization can also result from persistent exposure to painful input from the peripheral neurons. Together, the peripheral and central sensitization can lead to a postoperative hypersensitivity state or "spinal wind-up" that is most unpleasant for the patient and the surgeon.
To help prevent this, preemptive analgesia with intra-articular local anesthetics or morphine can be very helpful. Studies have demonstrated that even one to two milligrams of morphine injected intra-articularly can provide effective postoperative analgesia for several hours without any systemic side effects. The mechanism of action appears to be through binding specific receptors in the nerve terminals within the joints. A low level of inflammation appears to increase the affinity for binding and the effect. The addition of an oral nonsteroidal antiinflammatory agent can suppress benefits of the intra-articular morphine administration, but the downside of this is probably outweighed by the benefit of reduced inflammation and potential for the hypersensitivity state. Combining intra-articular morphine with long-acting bupivacaine is an effective way to block patient’s pain for the initial four to eight hours after surgery. The addition of intra-articular Ketorolac provided similar benefit in analgesia but no additive effect when combined with intra-articular morphine. Intra-articular corticosteroids can be used in similar fashion but there are safety concerns regarding potential infection. Adding intra-articular clonidine to bupivacaine and morphine appears to potentiate the effects of these drugs when used individually.
Regarding oral narcotic administration, long-acting opioids with controlled release formulations provide increased convenience as well as pain relief for the patients, especially during sleep. Side effects including sedation, sleep disturbance, and vomiting are also reduced. This in combination with a potent anti-inflammatory agent such as ketorolac can be very beneficial in the first few days following outpatient ACL reconstruction. The newer Cox-2 inhibitors are also effective at reducing pain while avoiding gastrointestinal side effects. It appears that the Cox-2 pathway is specific for pain, whereas, the Cox-1 pathway, which is also addressed by other anti-inflammatory drugs, is responsible for more of the toxicity. Additional modalities include administration of a femoral nerve block intra-operatively with a long-acting agent such as ropivacaine or bupivacaine. The maximum safe dose of bupivacaine for peripheral nerve block is 2 mg/kg of body weight. Lastly, cryotherapy can decrease pain, swelling, inflammation and bleeding postoperatively. Cooling can also depress the neuronal pain signal transmission and reduce muscle spasm. Ideally, the skin temperature should be lowered to about 20°C to obtain measurable changes in intra-articular temperature.
Optimal pain relief allowing normal function is difficult to achieve with a single drug or single method. It is currently recommended that combined regimens or multi-modal analgesia be used following arthroscopic knee surgery. This is especially important following ACL reconstruction to allow this procedure to be performed as an outpatient. Preemptive analgesia can include administration of the Cox-2 anti-inflammatory agents, which do not have any antiplatelet or bleeding effects. This in combination with femoral nerve blocks and intra-articular administration of bupivacaine plus morphine is very effective in the immediate postoperative period. Multi-modal oral medications to include long acting opioids plus an anti-inflammatory preparation and cryotherapy are also important additions in the postoperative phase. This combination can help us keep our patients comfortable, happy, and deliver care in a cost efficient manner.