Analgesic Benefits of Genicular Nerve Blocks of the Posterior Knee for Patients Undergoing ACL Reconstruction

Overview

Outpatients scheduled to have ACL surgery typically receive a femoral nerve block to provide analgesia for the front of the knee. Postoperatively, these patients will often report pain in the back of the knee. Local anesthetic infiltration of the posterior aspect of the knee results in blockade of the genicular nerves of the posterior knee. These nerves originate off of the tibial and common peroneal nerves and their blockade will result in improved posterior knee pain relief and may decrease narcotic consumption compared to patients who receive the same infiltration with normal saline.

Femoral nerve blocks are commonly used to provide postoperative analgesia for ACL surgery. The limitation of these blocks is the incomplete analgesia they provide of the knee joint subjecting the patient to posterior knee pain. As a result, some of these patients receive rescue sciatic blocks in the postoperative care unit to cover posterior knee pain. The sciatic block provides excellent analgesia for the posterior knee; however its blockade invariably affects other territories of the sciatic nerve such as the lower leg and foot. For ACL surgery, the loss of sensation and/or motor strength to this area is unnecessary and may make ambulation more difficult. The ability to ambulate with minimal assistance may be more important for a patient undergoing an outpatient surgery when compared to an inpatient surgery. At the posterior knee, the sciatic nerve branches off into the tibial and common peroneal nerves which give rise to sensory fibers that innervate the posterior knee. We propose targeting these terminal fibers in the popliteal fossa by infiltrating local anesthetic between the distal femoral shaft and popliteal artery thereby providing posterior knee analgesia without affecting the lower leg.This application of this block has not been studied in patients having ACL surgery. A single interim analysis is scheduled after the data for 50 cases are available.