A Comparison of the Effects of Continuous and Single-Shot Adductor Canal Blocks on Analgesia and Knee Flexion Following Total Knee Arthroplasty

Introduction

Total knee Arthroplasty (TKA) is the standard treatment for knee osteoarthritis, which affects millions of people world wide. In 2008, more than 600,000 TKAs were performed in the United States. This number represents more than double the number performed in 1999 and is estimated to increase by more than 500 % (from the 1999 value) by 2020.

Severe postoperative pain occurs in 60% and moderate pain in 30% of patients undergoing TKA. In addition, the intensity of acute postoperative pain correlates with the risk of developing a persistent post surgical pain which can be chronic and debilitating. Thus, the management of pain following TKA is an important determinant of a patient's long term functional outcome. In addition, recovery from TKA requires extensive and effective postoperative physiotherapy (PT), itself a painful event following TKA. Physiotherapy ensures good range of motion and prevents complications such as tissue retraction, adhesion formation and muscle atrophy, all of which may compromise achievement of long term recovery milestones. Thus, the anesthesiologist caring for patients undergoing TKA attempts to provide a postoperative analgesic regimen which ensures that the patient is as pain free as possible while ensuring that the patient has sufficient motor strength to participate actively in PT.

The need to find non-narcotic alternatives for post surgical pain management has become even more urgent recently due to the recent epidemic of narcotic-related deaths. In the United States the number of opioid related deaths since 1999 has reached almost half a million which represents a four fold increase in incidence, and at least half of opioid related deaths involve prescription drugs. Hence effective non-narcotic approaches to pain management hold great importance not only for clinical care but also for public health on a larger scale.

Previously, intravenous, intrathecal or oral opioids were the mainstay of postoperative analgesia following TKA. Although variably effective, the resulting analgesia is associated with well recognized adverse effects including nausea, vomiting, pruritus and sedation. Each adverse effect is unpleasant and likely to impede recovery and participation in PT. Epidural catheters and femoral nerve blocks have both been used for postoperative analgesia in this setting, but each is associated with lower limb motor weakness which hinders early implementation of PT and may increase the risk of falls.