A Comparative Study Between Continuous Epidural Analgesia Versus Ultrasound Guided Continuous Femoral Nerve Block (CFNB) Versus Ultrasound Guided Continuous Adductor Canal Block (ACB) for Post-operative Pain Management After Total Knee Replacement (TKR).

All patients will be assessed preoperatively, and will be instructed to fast for 8 hrs. On arrival to the operation theatre, Intravenous access will be established, and Ringer's solution will be infused as a co-load fluid bolus. Monitors for non-invasive blood pressure, heart rate, electrocardiogram (ECG), and pulse oximetry (SpO2) will be used to monitor the perioperative vital parameters of patients.

Before the spinal anesthesia, the epidural catheter will be inserted, while the femoral and adductor canal catheters will be inserted under ultrasound guidance before spinal anesthesia according to patient group allocation by single operator.

Group A: As for the epidural analgesia, it will be performed under complete aseptic precautions, by introducing a needle between the lumbar vertebrae at level of L3-L4 or L4-L5 and injecting anesthetic medication into the epidural space, via the epidural catheter inserted through the needle into the epidural space.

The epidural needle (typically 18-gauge and 8.89 cm (3.5 inches) in length) is inserted in the midline of the patient's back, defined by the spinous processes at the chosen spinal level. A skin wheal is raised with 1% lidocaine using a 25-gauge needle in the midline of the spine, in the lower third to half of the interspace. The subcutaneous tissue is infiltrated with lidocaine and is continued through supraspinous ligament down to the interspinous ligament.

The epidural needle is inserted with stylet at a straight or slight cephalad angle or at steeper cephalad angle. The needle bevel is oriented cephalad while the patient is in a sitting position. The needle is advanced through the supraspinous ligament and into the interspinous ligament. A firmness in the tissue suggests that the tip of the needle is in the supraspinous or interspinous ligament. Lack of firmness may indicate a paraspinous position of the needle tip, and the needle should be adjusted.