Paralysis of the joint being operated on is important for placement of a prosthesis and passive ROM, so spinals or epidurals are typical choices for regional anesthestia in total knee arthroplasties. Although both are appropriate techniques, your choice could be based on the patient’s age, as younger patient’s have a higher risk of spinal headaches following a dural puncture (i.e. you may decide to do an epidural for younger patients). Coverage from T12 to S2 is adequate, but you may want to extend up to T8 for a tourniquet.
Typical drugs would be: Spinal: 15 mg 0.75% bupiv w/ 0.2 mg morphine. Epidural: 15-20 ml 2% lidocaine w/ epi 1:200,000 in divided doses.