"Comparison of Intra-articular of 0.2% Ropivacaine vs. 0.75% Ropivacaine in Postoperative of Knee Arthroscopy"

All patients with acute lesions that attend the orthopedic and trauma center of the ABC medical center are invited to participate in the study. Those that meet the inclusion criteria and later sign an informed consent are randomized to receive 10 ml of a solution with ropivacaine at 0.75% and 0.2% intraarticular for the first 5 minutes after the end of surgery (closing of surgical wounds). Both the patient, the physician who applies it and the evaluator of outcomes remain blinded to the dose of ropivacaine the patient receives.

Two hours after the end of the surgery, while the patient is in his room, the presence of pain is evaluated by a visual analog scale (VAS), while the patient is asked to flex and extend his knee. The result is quantified continuously, to later categorize the pain in none to slight pain (0-3 points) and moderate-severe pain (4-10 points). All the information is recorded on established forms in the clinical file (general data), that includes the variables of interest for the study, and is reported by the physicians after standardization of all those in charge with collecting information to comply with the conceptual and operative operationalization of the variables described in the research protocol. In addition to the evaluation of pain, the administration of opioids to patients for necessary reasons (presence of pain) by the physicians in charge is recorded.

It is hoped that, in patients with knee arthroscopy for acute lesion, there is a difference in the frequency of moderate-severe pain of 30% in the post-operative (frequency of 37.5% in patients with ropivacaine at 0.2% and frequency of 0.75% in patients with ropivacaine at 0.75%).

In previous studies the prevalence of moderate-severe intensity pain in patients post knee arthroscopy is 71.2%, and the prevalence of acute pain in post-operative is 37.5%, surpassing the prevalence when compared with other surgical procedures of various specialties.

The administration of opioids is part of common practice in managing pain. However, it represents a risk for patients due to adverse effects and the high risk of dependence. It is necessary to seek alternatives that reduce the consumption of opioids in patients post knee arthroscopy.

Characteristics of the patients reported in other studies, such as sex, body mass index, sedentarism, the cause, duration and use of tourniquet in surgery, in addition to the type of lesion of articular cartilage and the presence of neuropathies, may influence in the presence of pain severity.

Eligibility Criteria:
Inclusion Criteria:

* Mental health: healthy (not taking any medication)
* Articular cartilage lesion Grade I, II or III by Outerbridge
* Elective knee surgery
* Patients with any of the following diagnoses:
* Simple meniscal lesion
* Lesion of a single knee (unilateral)

Exclusion Criteria:

* Neuromotor diseases (alterations in step, strength or sensitivity)
* History of knee surgery (orthopedic)
* Instability that includes knee ligament lesions
* Addictions
* Mental diseases in medical treatment
* Hepatic diseases
* Allergy to any of the medications used in the study
* Epidural or peridural anesthesia
* Chronic pain in treatment
* Postoperative drain of knee arthroscopy
* Pregnant or lactating