ASRA Pain Medicine Update

This article originally appeared in the February 2019 issue of ASRA News.

Introduction

Controlling posterior knee pain after total knee arthroplasty is an important component of the comprehensive strategy for providing postoperative analgesia. This pain is mediated by articular branches that originate primarily from the tibial component of the sciatic nerve with contributions from the obturator nerve (Figure 1) ^[1],[2]. Posterior knee pain can be controlled by sciatic nerve block, but leads to undesirable foot drop and may delay diagnosis and treatment of surgically induced common peroneal nerve injury. A selective tibial nerve block in the popliteal fossa is an alternative to sciatic nerve block and can provide analgesia without causing a foot drop, but it decreases sensory perception in the sole of the foot and causes weakness of plantar flexion ^[3].

The goal of iPACK is to selectively block only the innervation of the posterior knee joint while sparing the main trunks of tibial and common peroneal nerves, thereby maintaining the sensorimotor function of the leg and foot.

The articular branches, after arising from the main trunks of the tibial and obturator nerves, travel through a tissue space between the popliteal artery and the femur to innervate the posterior capsule of the knee (Figure 2). These articular branches can be blocked by infiltrating this tissue plane between the popliteal artery and the capsule of the knee (iPACK) with local anesthetic solution under ultrasound guidance. The goal of iPACK is to selectively block only the innervation of the posterior knee joint while sparing the main trunks of tibial and common peroneal nerves, thereby, maintaining the sensorimotor function of the leg/foot. We introduced the iPACK technique at the American Society of Regional Anesthesia (ASRA), Spring meeting in 2012 ^[4].

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