The recent success of adductor canal block in providing post-operative analgesia, along with the prospects of early ambulation has evoked interest in studying the effects of local anesthetics like ropivacaine, and some adjuvants like dexmedetomidine. Both ropivacaine and dexmedetomidine have been effectively and safely used in the past in other peripheral nerve blocks.The aim of this study is to compare the duration of analgesia of adductor canal block using ropivacaine with and without dexmedetomidine after unilateral total knee arthroplasty.

Written informed consent will be taken from all patients meeting the inclusion criteria. They will be randomized into two groups, group A and group B on the basis of a computer generated randomization table. After standard overnight fasting, all the patients will be given a subarachnoid block with 2.5 ml 0.5 % hyperbaric bupivacaine and 25 μg fentanyl for the surgery. Intravenous (iv) dexamethasone 8 mg and 0.02 mg/kg midazolam will be given to all patients. Standard monitoring and iv fluids (balanced salt solution) will be continued during the surgery. After the completion of surgery, the patients will receive ultrasound guided adductor canal block (needle in-plane with the transducer) in the post-operative room using 21 G 10 cm short bevel needle with a 25 cm long injection line. Group A will be given 20 ml of 0.375% ropivacaine with 5 ml saline and Group B will receive 20 ml of 0.375% ropivacaine with 0.25μg/kg dexmedetomidine diluted in a 5 ml volume saline. The drug will be injected below the sartorius and lateral to the femoral artery and the drug spread will be confirmed real time on the ultrasound monitor.

Intravenous paracetamol 15 mg/kg will be given in the ward and repeated orally 8 hourly. One dose of iv diclofenac 50 mg will be given to all patients 2 hr after they reach the ward. Oral pregabalin and etoricoxib will be repeated in the evening.

The ward nurse who is blinded to the study groups will collect the data in the post-operative period. Heart rate, NIBP and SpO2 will be noted every 15 min for the first hour, and every 2 hr till 24 hr. Bradycardia and hypotension will be considered as 20% decrease from baseline and will be treated with iv atropine and mephentermine respectively. Any adverse event such as nausea vomiting, giddiness, signs of local anesthetic toxicity etc. will be noted. Pain will be assessed by the Numeric Rating scale (1-10, 1 being the least and 10 being the worst pain described by the patient). Motor strength will be assessed as per the Medical Research Council Scale as 0-5 at 6, 12, 18 and 24 hr after the block.

Time to first rescue analgesia (in the form of iv tramadol 50 mg) will be noted along with the total tramadol consumption in 24 hr. The physiotherapist will assess the patients on POD1 and assist them to ambulate with support. The time to ambulate will be noted by the nurse. She will also note the patient satisfaction score at 24 hr post operatively; 1-not satisfied, 2-satisfied. The data will be compiled and appropriate statistical tests will be used to analyze it.