Local anesthesia is an important component of multimodal pain management during the perioperative period for total knee arthroplasty, particularly with increased emphasis on early mobilization and decreased length of stay. Periarticular injections and regional nerve blocks are both effective in providing short-term pain relief when administered in isolation, and multiple randomized controlled trials have demonstrated that when administered in conjunction with one another, they also provide a synergistic effect.~Periarticular injections are the simplest mechanism for infiltrating the surgical site with analgesic medications, and these provide effective pain relief. One described technique involves infiltrating this mixture into the lateral femoral periosteum, posterior capsule, medial periosteum, capsule and skin during various portions of a total knee arthroplasty. This is the technique used in our practice.~Regional nerve blocks also have beneficial effects on pain, early mobilization and length of stay. Traditionally, anesthesiologist-administered femoral nerve blocks were utilized for this purpose. The femoral nerve consists of 4 main branches:the terminal portion of the vastusmedialis branch innervates the medial collateral ligament (MCL). The terminal portion of the vastusintermedius branch innervates the anterosuperior aspect of the knee capsule. The terminal portion of the vastuslateralis branch does not innervate the knee capsule. The saphenous nerve is the terminal sensory branch of the femoral nerve and travels in the adductor canal. It gives off an infrapatellar branch which exits the adductor canal to innervate the skin on the anteromedial aspect of the knee and the anteroinferior aspect of the knee capsule. Blockade of the entire femoral nerve results in significant quadriceps motor deficits.~Adductor canal blocks can be targeted to anesthetize only the saphenous branch of the femoral nerve, however, and this spares the motor innervation to the quadriceps. Multiple randomized controlled trials have shown that these adductor canal blockades provide equivalent analgesic effects to femoral nerve blocks without associated deficits in quadriceps strength. In one study, quadriceps strength was measured immediately prior to and immediately following placement of femoral and adductor can blocks in patients undergoing TKA. After the femoral block, quadriceps strength decreased to 16% of the baseline pre-block value. After the adductor-canal-block, however, strength increased to 193% of the pre-block value. MRI measurements, cadaveric injections, and dissections have shown that a surgeon-performed injection of the saphenous nerve from within the knee after it exits from the adductor canal is a feasible procedure, and a randomized controlled trial found that a surgeon-administered adductor canal blockade was non-inferior to the traditional adductor canal blockade administered by an anesthesiologist. This technique is simple and can be easily performed during administration of a periarticular injection. It is unclear based on the current literature whether this surgeon-administered adductor canal blockade provides a synergistic effect on pain relief when combined with a periarticular injection.~Treatment Group:~The treatment group will consist of patients undergoing total knee arthroplasty who receive standardized 100 cc periarticular injection into the lateral femoral periosteum, posterior capsule, medial periosteum, capsule and skin. Patients will then receive 10cc of ropivacaine into their adductor canal. This will be administered by injecting into the adductor canal without dissecting down to the saphenous nerve and without ultrasound guidance.~Comparison (Control) Group:~The control group will consist of patients undergoing total knee arthroplasty who receive a standardized periarticular injection into the lateral femoral periosteum, posterior capsule, medial periosteum, capsule and skin. Patients randomized in this group will then receive 10cc of saline into their adductor canal. This will be administered by injecting into the adductor canal without dissecting down to the saphenous nerve and without ultrasound guidance.
The investigators aim to investigate whether the addition of a surgeon-administered adductor canal blockade to a multimodal periarticular injection cocktail provides additional pain relief for patients undergoing total knee arthroplasty. This study will help identify the effectiveness of surgeon-administered adductor canal blockade in perioperative pain control for patients undergoing total knee arthroplasty