Key points

Introduction

Total knee arthroplasty (TKA) is a frequently performed procedure, and its incidence is expected to increase 673% to 3.48 million procedures annually by 2030. Current literature confirms that TKA is an effective treatment for osteoarthritis with excellent outcomes. Despite these results, current postoperative pain management may be insufficient and prevent patients from sleeping, ambulating, and participating in physical therapy. Numerous strategies have been devised to control postoperative pain and reduce opioid consumption, including neuraxial anesthesia and peripheral nerve blocks. Continuous femoral nerve blockade, in particular, is associated with a 1.0% to 2.5% incidence of muscle weakness, nerve damage, and local infection, with 57% of catheters colonized at 48 hours.

In addition to peripheral nerve blocks, parenteral narcotics continue to be a mainstay of postoperative pain management despite significant side effects. Oderda and colleagues demonstrated that opioid-related adverse drug events after surgery were associated with significantly increased length of stay and hospitalization costs. With the goal of decreasing these adverse drug events, multimodal pain pathways have been developed to block pain at its source. Furthermore, a successful multimodal pathway should control pain but also maximize muscle control, promote rehabilitation, and decrease venous stasis. Periarticular injection (PAI), as an adjunct to multimodal pain management pathways, accomplishes these goals.

Evidence from the literature supports the use of PAI. In a study by Vendittoli and colleagues, morphine consumption was lower in the PAI group compared with the control group for up to 40 hours postoperatively. Other authors have compared different PAI protocols and reported that these are associated with lower narcotic consumption and pain scores compared with use of a femoral nerve block. In a recent prospective randomized trial by Chaumeron and colleagues, PAI provided equivalent pain control for up to 120 hours without the 37% incidence of motor blockade experienced by the group receiving a femoral nerve block. Patients who received PAI had an increased capacity to perform a straight leg raise, better active knee extension, and an increased ability to ambulate than those receiving a femoral nerve block. This article reviews the relevant neuroanatomy of the knee, with specific attention to the areas that are the most sensitive and should be infiltrated with an anesthetic.

Introduction

Total knee arthroplasty (TKA) is a frequently performed procedure, and its incidence is expected to increase 673% to 3.48 million procedures annually by 2030. Current literature confirms that TKA is an effective treatment for osteoarthritis with excellent outcomes. Despite these results, current postoperative pain management may be insufficient and prevent patients from sleeping, ambulating, and participating in physical therapy. Numerous strategies have been devised to control postoperative pain and reduce opioid consumption, including neuraxial anesthesia and peripheral nerve blocks. Continuous femoral nerve blockade, in particular, is associated with a 1.0% to 2.5% incidence of muscle weakness, nerve damage, and local infection, with 57% of catheters colonized at 48 hours.

In addition to peripheral nerve blocks, parenteral narcotics continue to be a mainstay of postoperative pain management despite significant side effects. Oderda and colleagues demonstrated that opioid-related adverse drug events after surgery were associated with significantly increased length of stay and hospitalization costs. With the goal of decreasing these adverse drug events, multimodal pain pathways have been developed to block pain at its source. Furthermore, a successful multimodal pathway should control pain but also maximize muscle control, promote rehabilitation, and decrease venous stasis. Periarticular injection (PAI), as an adjunct to multimodal pain management pathways, accomplishes these goals.

Evidence from the literature supports the use of PAI. In a study by Vendittoli and colleagues, morphine consumption was lower in the PAI group compared with the control group for up to 40 hours postoperatively. Other authors have compared different PAI protocols and reported that these are associated with lower narcotic consumption and pain scores compared with use of a femoral nerve block. In a recent prospective randomized trial by Chaumeron and colleagues, PAI provided equivalent pain control for up to 120 hours without the 37% incidence of motor blockade experienced by the group receiving a femoral nerve block. Patients who received PAI had an increased capacity to perform a straight leg raise, better active knee extension, and an increased ability to ambulate than those receiving a femoral nerve block. This article reviews the relevant neuroanatomy of the knee, with specific attention to the areas that are the most sensitive and should be infiltrated with an anesthetic.

Methods

The current available literature on knee neuroanatomy, pain generators, and concentrations of mechanoreceptors were reviewed. The databases searched include MEDLINE, MEDLINE In-Process, EMBASE, BIOSIS, ClinicalTrials.gov , and Cochrane Database of Systematic Reviews. Full text searching of key surgical journals was also performed. Searches were not restricted by study design, publication year, or language, and conference proceedings and abstracts were included in the search. Reference lists of all included studies were scanned to identify additional relevant studies. Search terms included “knee innervation,” “pain control,” ”knee mechanoreceptor,” “sartorial nerve,” “saphenous nerve,” “common peroneal nerve,” and “tibial nerve.” Studies were excluded if they did not provide pertinent information on human knee innervation or were not published in English. The search produced 56 articles, of which 15 met inclusion criteria. This article summarizes human knee innervation and relevant areas of increased mechanoreceptors.

Neuroanatomy

The degree to which the intraarticular components of the knee generate neurosensory signals that reach the spinal, cerebellar, and higher central nervous system levels is variable. These signals ultimately result in conscious perception. Biedert and colleagues performed a histologic examination of free nerve endings in the human knee to describe which intraarticular areas contain increased nerve endings and mechanoreceptors. They found that the retinacula, patellar ligament, pes anserinus, and ligaments of Wrisberg and Humphry had the greatest number of free nerve endings, whereas the lowest number was found in the anterior cruciate ligament (ACL). In a correlate study by Dye and colleagues, conscious patients underwent knee arthroscopy without anesthesia and were able to identify which areas of the knee were more painful on arthroscopic palpation. The following 8 knee regions have been identified as having increased neurosensory perception and an elevated concentration of mechanoreceptors: (1) suprapatellar pouch and quadriceps tendon, (2) medial retinaculum, (3) patellar tendon and fat pad, (4) medial collateral ligament and medial meniscus capsular attachment, (5) posterior cruciate ligament (PCL) tibial attachment, (6) ACL femoral attachment, (7) lateral collateral ligament and lateral meniscus capsular attachment, and (8) lateral retinaculum ( Fig. 1 ). The nerve contributions to each zone are discussed in the following sections.

The 8 regions of the knee ( red markings ) that have increased pain receptors.

( From Best Infiltration Practices Local Analgesia Infiltration Techniques – Hip & Knee Arthroplasty. Copyright © 2014. All rights reserved GuidelineCentral.com , with permission from International Guidelines Center ( guidelinecentral.com ); and Courtesy of Erin Daniel, with permission.)