Comparison of Acetaminophen and Platelet-rich Plasma Therapy for the Treatment of Knee Osteoarthritis.

This is a randomized controled study. Patients enroled in the study will be divided into two groups (calculated n=30 per group). One group will be treated with acetaminophen (500 mg/8 h) for 6 weeks, the experimental group will receive a total of 3 intra-articular injections of PRP, one injection every 2 weeks. The intake of any other analgesic or anti-inflammatory drug will be prohibited in patients from two groups.

For those who received the infiltrations, the procedure consist of a 27-mL venous blood sample in 6 vacutainer tubes with sodium citrate 0.109 M for each injection. Samples are gently agitated to ensure mixing the anticoagulant with the blood. An extra tube with anticoagulated EDTA blood is obtained for initial platelet count. Blood samples are centrifuged for 10 minutes at 1800 rpm to separate the erythrocyte layer. The upper plasma layer is carefully collected in a new sterile propylene tube trying not to remove the leukocyte layer. Plasma from all tubes is centrifuged again for 12 minutes at 3400 rpm to obtain a two-part plasma: the upper part consisting on platelet-poor plasma and lower part consisting of platelet-rich plasma (PRP). The platelet-poor plasma is discarded to obtain a final volume of 3 mL. This volume, consisting of PRP, is mixed carefully through pipetting to resuspend platelets and it was then transferred to a new sterile glass tube. An aliquot of the final PRP is sent to the laboratory for platelet count. All open handling sample procedures are performed within a high-efficiency particulate air-filtered laminar flow hood.

Application of injections is carry out after disinfection of skin in the knee joint area. After local anesthesia with lidocaine chlorohydrate, platelets are activated using 10% calcium gluconate solution and the liquid PRP is injected in a sterile condition using a 22 G needle. The needle is inserted using the superolateral approach in an angle of approximately 45°.

Patients from PRP group will be asked to flex and extend their knees immediately after injection so that PRP could distribute adequately across the joint space. After 5-10 minutes of observation the patients are sent home with written indications including to have relative rest 24 to 48 hours after the injection, the use of cold therapy for 15 minutes three times a day and 500 mg of acetaminophen in case of pain and inflammation.

The use of NSAIDs or any steroids is prohibited. All the patients will be evaluated before the beginning of their respective treatment and at 6, 12 and 24 weeks after. Three different scales are used to evaluate clinical outcome, the VAS (Visual Analog Scale) that scores pain level, the WOMAC (Western Ontario and McMaster Universities Arthritis Index) which assesses pain, articular stiffness and functional limitation, and the Spanish (México) version of the SF-12 (Short Form-12) for assessment of quality of life.