➢ Peripheral nerve blocks are an often-utilized and efficacious method of analgesia for orthopaedic surgery about the knee.
➢ Benefits include decreased pain and narcotic use, increased participation in postoperative physical therapy, and decreased length of hospital stay.
➢ Adductor canal blocks have the advantage of preserving quadriceps function for early postoperative range of motion and walking.
➢ The risk of serious complications resulting from a peripheral nerve block is relatively low, ranging from 0% to 3%.
A peripheral nerve block is the modality of regional anesthesia in which a local anesthetic is injected around a peripheral nerve, blocking sensory and possibly motor function. Peripheral nerve blocks are becoming an increasingly popular method of analgesia for orthopaedic surgery involving the lower extremity1,2. A regional block is effective for managing perioperative pain, has a low risk profile, and has been shown to reduce opioid use and subsequent side effects1,3,4. The use of peripheral nerve blocks is also associated with early mobilization and participation in physical therapy, decreased length of hospitalization, and improved discharge rates from the ambulatory-care setting1. Early walking has been shown to reduce the risks of infection, deep venous thrombosis (DVT), and arthrofibrosis, the 3 most common causes of hospital readmission following total knee arthroplasty5.
Femoral nerve blocks are one of the most commonly used methods for providing regional anesthesia for knee surgery1,6. While the overall frequency of use is still fairly low, the rate of femoral nerve blocks for anterior cruciate ligament (ACL) reconstruction is increasing7. The use of femoral nerve blocks in the setting of either arthroscopic or open knee surgery improves early postoperative pain control, promotes early mobilization with physical therapy, provides cost savings, and improves patient satisfaction compared with the use of intravenous opioids alone1. More recently, the adductor canal block has come into favor because of its ability to provide similar analgesia at the surgical site while sparing the majority of quadriceps innervation, which, in turn, promotes early walking. A sciatic or popliteal nerve block is often performed in conjunction with a femoral nerve block to control posterior knee pain after total knee arthroplasty, but the effectiveness is still unclear8,9.
The present article provides a comprehensive review of peripheral nerve blocks used for arthroscopic knee surgery and total knee arthroplasty, with a focus on anatomy, indications, technical considerations, complications, and patient outcomes.
The knee is innervated by branches of the femoral, obturator, and sciatic nerves, but there is no consensus on the number or origin of the articular branches from these nerves10. There are 2 groups of articular nerves that are distributed to the knee: an anterior division and a posterior division11. The anterior division consists of articular branches of the femoral, common peroneal, and saphenous nerves, whereas the posterior division consists of articular branches of the tibial and obturator nerves. Hirasawa et al. reported that the ACL is innervated by nerves to the anterior aspect of the capsule and that the posterior cruciate ligament (PCL) is innervated by nerves to the posterior aspect of the capsule12.
The femoral nerve runs deep to the inguinal ligament and is positioned lateral to the femoral artery. It branches to innervate muscles and skin in the anterior compartment of the thigh. The branch to the vastus medialis muscle terminates as the medial retinacular nerve, which enters the knee capsule deep to the medial retinaculum and gives off a branch to the medial collateral ligament (MCL) and then ramifies over the superomedial aspect of the knee13. The vastus intermedius branch of the femoral nerve exits the substance of the vastus intermedius muscle and travels in periosteal vessels on the anteromedial aspect of the femur before it enters the anterosuperior aspect of the knee capsule. Branches of the nerve to the vastus lateralis terminate near the quadriceps tendon but do not innervate the knee capsule13. The saphenous nerve, which travels in the adductor canal, is the terminal sensory branch of the femoral nerve. Its main trunk gives off an infrapatellar branch at variable distances along the thigh13. The infrapatellar branch exits the adductor canal and courses medially toward the tibial tuberosity as it innervates the skin on the anteromedial aspect of the knee (distal to the patella) and the anteroinferior aspect of the knee capsule itself13.
The obturator nerve travels through the obturator foramen and splits into anterior and posterior divisions14. The anterior division innervates many of the muscles in the medial aspect of the thigh and the skin of the inferomedial aspect of the thigh, but it does not send articular branches to the knee13,14. The posterior division travels in the adductor canal and exits through the adductor hiatus, bound by fascia to the popliteal artery13. A motor branch supplies the adductor magnus muscle, and sensory branches to the knee joint innervate the articular capsule, cruciate ligaments, and synovial membrane14.
The sciatic nerve arises from the greater sciatic foramen and travels in the posterior compartment of the thigh. It divides into the tibial nerve and the common peroneal nerve, frequently at the middle part of the thigh; however, there is some variability of the level of bifurcation. The tibial nerve continues in the popliteal fossa, giving off articular branches, which pierce through the popliteal adipose tissue and follow superomedial and superolateral popliteal vessels to innervate the articular capsule12. Articular branches from the common peroneal nerve, which are given off as it courses along the medial edge of the long head of the biceps femoris muscle, innervate the posterior and lateral aspects of the articular capsule. The common peroneal nerve also gives off a recurrent articular branch as it passes into the lateral aspects of the leg, which innervates the anterolateral aspect of the articular capsule12.
Lower-extremity nerve blocks are widely used for procedures requiring analgesia of the surgical field but not requiring neurological monitoring. Ease of performance, patient cooperation, risk of complications, and desired clinical outcome are some of the parameters to be assessed prior to their execution. The regional distribution of each nerve sometimes necessitates the use of multiple blocks to achieve total analgesia. Mastery of technique by the clinician performing the procedure may influence block selection. A femoral block is indicated for surgery localized to the anterior aspects of the thigh and knee. Combination with a sciatic nerve block can provide total anesthesia to the middle part of the thigh through the remainder of the lower extremity15,16. The adductor canal block is now frequently used in place of a femoral nerve block. This procedure targets the femoral nerve distal to the motor branches to the quadriceps, thereby providing analgesia to distal areas of the thigh and femur while allowing for considerable motor sparing and hence early walking17. The sciatic nerve block is typically used in concert with the aforementioned blocks to provide total analgesia to the lower extremity but theoretically could be used independently for knee, leg, or foot surgery isolated to the region of innervation. The sciatic nerve block can be performed through multiple approaches (anterior, transgluteal, subgluteal, and popliteal) and allows for administration in various positions to accommodate patient comfort (Table I).
Informed consent is obtained prior to performing a peripheral nerve block to ensure that the patient understands the benefits of preoperative nerve block for reducing intraoperative and postoperative narcotic requirement. However, the procedure itself is frequently not well tolerated, especially for deeper blocks in the lower extremity. Needle depth and muscle contraction during nerve stimulation can add discomfort at the site of the preexisting pathological abnormality. Light sedation, therefore, is frequently necessary to allow for successful completion of the procedure. Limiting the depth of sedation has several benefits: (1) it allows for coaching of the patient to maintain optimal positioning, (2) it allows for more clarity from the patient regarding the monitoring of possible complications, and (3) it allows for performance of the block in a preoperative area. The placement of a nerve block with the patient under deeper levels of sedation is a subject of concern for anesthesiologists because of an inability to observe signs of intraneural injection or local anesthetic systemic toxicity. The American Society of Regional Anesthesia and Pain Medicine (ASRA) practice guidelines do not support the practice of performing regional nerve blocks with patients under deep sedation or general anesthesia as warning signs of needle-to-neuraxis proximity, which are important indicators of anatomic location, are absent. However, there may be a role for heavy sedation for populations of patients who would otherwise be unable to tolerate the procedure (i.e., patients with dementia, patients with developmental delay, or pediatric patients)18. The equipment used to perform a peripheral nerve block with use of a nerve stimulator and/or ultrasound is shown in Figure 1.
The incorporation of nerve stimulation during the placement of a peripheral nerve block dramatically increases the success rate of the procedure19. The nerve stimulator produces a low-intensity current that, when contacting a specific nerve bundle, will elicit a corresponding muscle twitch in the fiber innervated. In the past decade, clinicians have transitioned to using ultrasound guidance as a primary tool for accurate needle placement (Figs. 2 and 3). A recent meta-analysis evaluating this practice demonstrated significantly improved success rates (p < 0.001), procedure times (p = 0.003), and onset times (p = 0.001) across all peripheral nerve blocks combined20. Data suggest that, with improved needle positioning via ultrasound, the effective anesthetic volume required to deliver an adequate femoral block is reduced, thereby decreasing the risk of local anesthetic toxicity21. To date, the ASRA has not definitively supported 1 method of enhanced needle guidance (e.g., nerve stimulation or ultrasound) over another, claiming that data are not currently sufficient to define any broad practice guidelines. Their current recommendation states that ultrasonography is not an inferior method for assisting needle positioning and should be used in combination with, not instead of, nerve stimulation to provide clinicians with more tools to minimize risk to the patient22. The ultrasonographic anatomy that is visualized when performing a femoral and an adductor canal block is shown in Figures 4 and 5, respectively.
There are no current practice guidelines supporting the use of a particular local anesthetic agent or dose over another. As a result, the choice of anesthetic is largely block and operator-specific. Short and long-acting anesthetics can be used either as single agents or in concert, depending on the goal. Blocks delivered for the purpose of postoperative pain control may utilize long-acting agents, whereas blocks intended to provide the primary form of anesthesia for a procedure may require a short-acting agent to improve onset time. Adding short-acting lidocaine to a bupivacaine or ropivacaine femoral-sciatic block decreases both onset time and complete block time. This improvement comes at the expense of decreasing the total time that the now-reduced concentration of long-acting agent will remain in plasma23. The final volume delivered to a finite space and the dose given to minimize the risk of anesthetic toxicity largely affect this decision. When considering long-acting agents, onset and duration times and cellular toxicity commonly govern selection. Clinically important increases in neurotoxicity and cardiotoxicity have been shown in association with bupivacaine. While the gross appearance of skeletal muscle does not change, histological studies have exhibited markedly increased permanent damage (calcific myonecrosis, scar tissue, and fiber regeneration) on exposure to bupivacaine as compared with ropivacaine24. Pharmacokinetic comparisons of agents have demonstrated that ropivacaine exhibits an optimal onset similar to that of mepivacaine while providing a longer duration of action25,26. Studies measuring the kinetics of levobupivacaine have demonstrated activity similar to that of ropivacaine27. The transition toward use of ropivacaine and levobupivacaine (rather than bupivacaine) is largely due to their improved pharmacokinetics and decreased cytotoxicity.
Continuous Nerve Block
Indwelling catheters placed during peripheral nerve block provide a useful adjunct to postoperative pain management. Successful placement of these catheters may be operator-dependent; however, prospective trials have demonstrated very low rates of serious complications such as paresthesias and neural lesions. The most common adverse event is bacterial colonization of the catheter, but this event is not associated with any clinically important long-term consequences28. When multiple postoperative pain management modalities have been compared, data have suggested that peripheral nerve blocks are associated with better pain scores than patient-controlled analgesia (PCA) using opiates and with fewer side effects than epidural anesthesia29. A recent study by Fowler et al. demonstrated that peripheral indwelling catheters were associated with better knee flexion, faster walking, and shorter hospital stays following total knee arthroplasty in comparison with systemic analgesia alone30. The use of an indwelling peripheral catheter avoided the increased rates of urinary retention and hypotension seen in association with epidural catheters and resulted in higher patient-satisfaction scores when compared with epidural catheters. Perhaps the most convincing argument for peripheral nerve catheters over PCA or epidural analgesia is the option to continue the therapy in the outpatient setting. Extensive oral and written instruction to patients, combined with telephone follow-up, can be facilitated for patients using femoral and popliteal catheters. Use of these catheters has been associated with minimal complications (0.2%) and infrequent interventions by an anesthesiologist (4.2%) in the outpatient setting31. The risks of over-sedation and catheter-site infection associated with PCA and epidural catheters, respectively, are great enough to limit their use to the inpatient setting.
The ASRA held 2 large-scale conferences to establish practice guidelines on anticoagulation following anesthetic procedures. These guidelines largely pertained to neuraxial anesthesia, with the Society stating that an international normalized ratio (INR) of 1.4 was the highest tolerated ratio for withdrawing neuraxial catheters. Guidelines remain less defined for peripheral nerve blocks and subsequent continuous catheters. The ASRA reported that an INR of <3.0 conveyed a 3% risk of perineural hematoma in a 3-month period32. Furthermore, a retrospective review of approximately 7,000 lower-extremity blocks (lumbar plexus, femoral, and sciatic) administered with use of continuous nerve catheters in patients receiving warfarin, low-molecular-weight heparin, and aspirin did not demonstrate an increased incidence of perineural hematoma33. Subsequent data have not been widely published; thus, the ASRA states that an individualized risk-benefit assessment should be performed prior to proceeding with a peripheral nerve block in the presence of pharmacological anticoagulation18. The ASRA encourages physicians to be conservative in their risk-assessment protocol18 (Table II).
An analysis of the most recent closed claims data by the American Society of Anesthesiologists (ASA) indicated that local anesthetic systemic toxicity (LAST) accounted for one-third of claims for death or permanent brain damage following the use of a regional anesthetic34. LAST presents as a constellation of neurological symptoms starting as auditory changes, perioral numbness, and agitation. Patients can then develop seizures, coma, or respiratory arrest. After central nervous system excitement, symptoms can progress to cardiovascular excitation (tachydysrhythmias) followed by depression (hypotension, bradycardia, and asystole). The severity and onset of symptoms are dependent on the systemic dose. Direct or partial intravascular injection is most commonly responsible, and signs and symptoms present in seconds. Excessively large anesthetic doses also can lead to LAST, albeit with a longer onset time. Emergent airway and cardiovascular support via intubation and the initiation of advanced cardiac life support is crucial to combating permanent damage via hypoxia or acidosis. Further supportive measures include the administration of benzodiazepines in the setting of seizure activity and the use of succinylcholine if tonic-clonic activity is persistent35. Provided that a stable airway and circulatory support are present, the initiation of lipid emulsion can enhance resuscitation. Lipid-soluble anesthetics will bind to this emulsion and be drawn away from the central nervous system and cardiac tissue36. The prevention of such an episode is critical, with clinicians paying close attention to total anesthetic doses administered. Ultrasonographic guidance also may facilitate the avoidance of vascular structures. An all-inclusive audit of 7,000 peripheral nerve blocks indicated that the incidence of LAST was 0.98 per 1,000 blocks, whereas data on 12,000 ultrasound-guided blocks demonstrated that the incidence of seizures was 0.08 per 1,000 blocks37,38 (Table II).
Nerve and Vessel Damage
The analysis of recent closed claims data by the ASA also demonstrated that 56% of claims involving peripheral nerve injury were for temporary symptoms believed to be block-related34. The mechanisms of peripheral nerve injury typically involved direct trauma resulting from needles or continuous catheters, or ischemia, compression, and neural stretch resulting from a mass effect (large-volume boluses, hematoma, or abscess). The duration of injury correlated with the extent of damage. Hematoma and abscess formation have been associated with an increased risk of compression; however, the addition of local vasoconstrictors to anesthetic dosing in order to lengthen block time also may prolong the presence of large volumes of anesthetic, causing compression of local vascular structures39. Deficits can be difficult to assess until after the block has resolved. Total deficits should prompt immediate surgical evaluation. Mild symptoms require observation and reassurance of the patient, with neurological follow-up 2 to 3 weeks after the event to ensure progressive improvement in symptoms. Slow, but progressive, resolution warrants limited intervention, although there is no guideline establishing when surgical options should be considered. Procedures involving surgical trauma or stretch, application of compressive dressings or casts, tourniquet inflation during surgery, and improper patient positioning also may contribute to the development of neurological injury40. Hematoma formation is likely to be secondary to arterial puncture during peripheral block or direct surgical trauma. Ultrasonographic assistance can help to decrease the risk of needle puncture. Complications stemming from hematoma formation are more severe in association with upper-extremity blocks; however, whenever bleeding is encountered during the placement of a block, the procedure should be aborted to avoid any further damage41,42 (Table II).
Peripheral block complications arising from aseptic single-injection procedures or bacterial colonization of continuous catheters are infrequent. The local infection rate has been reported to range from 0% to 3%, and the rate of abscess formation has been even lower, ranging from 0% to 0.9%. As previously mentioned, the rate of bacterial colonization has been reported to be as high as 57%, but with little clinical consequence. The rate of bacterial infection has been highest at continuous catheter sites that are commonly associated with an increased bacterial nidus (i.e., femoral and axillary block sites)43,44. Aseptic technique with chlorhexidine preparation, the use of short-bevel needles, and the use of an antibiotic regimen during continuous catheterization can decrease the incidence of colonization; however, the decreased incidence is not associated with an appreciable improvement in clinical course45,46 (Table II).
Patient-reported pain in the immediate postoperative period differs substantially between patients managed with a nerve block combined with systemic analgesia and those managed with systemic analgesia alone. Patients undergoing total knee arthroplasty and those undergoing major ligament reconstruction about the knee who were managed with systemic analgesia alone reported visual analog scores (VAS) for pain of 6.1 to 7.4 and 4.5 to 6.2, respectively47-54. Patients undergoing those procedures who were managed with femoral block reported VAS pain scores of 0.2 to 4.5 and 1.4 to 3.9, respectively47-54. Chan et al. reported substantial pain with movement at 24 hours after total knee arthroplasty in 86% of patients who were managed with PCA alone (n = 66), compared with 62% of those who were managed with a continuous femoral nerve block (n = 64) (p = 0.001)55.
Pain reduction is further demonstrated by the decreased use of narcotics among patients receiving peripheral nerve blocks. Pain reduction appears to be greater for patients undergoing arthroplasty than for those undergoing knee arthroscopy. The use of morphine PCA on the first postoperative day after total knee arthroplasty was reported to be 18.8 to 30 mg/d among patients who received PCA alone, 14.9 to 20 mg/d among those who received a single-shot femoral nerve block, and 2.6 mg/d among those who received a continuous femoral nerve block48,55,56.
The narcotic requirement for patients undergoing knee arthroscopy has varied in the literature and is, at least in part, related to the specific arthroscopic procedure performed. Contreras-Domínguez et al. found a decreased morphine requirement over the first 48 hours following ACL reconstruction in adults who received a block as compared with those who did not (4.5 versus 25.5 mg)51. Schloss et al. followed 376 pediatric patients who underwent arthroscopic ACL reconstruction and also found a decrease in narcotic use57. In contrast, Farid et al. found that pediatric patients who received block anesthesia during ACL reconstruction still required a high narcotic load of 25 mg in the first 24 hours (n = 23)58. In addition, Frost et al. reported no difference between block and non-block groups in terms of the requirement for Tylenol #3 (acetaminophen with codeine) following arthroscopic ACL reconstruction (n = 61)52.
Physiotherapy and Strength
The rate of participation in physical therapy on the first day after total knee arthroplasty has been reported to be greater for patients managed with nerve blocks than for those managed with intravenous and oral analgesia alone (96.4% compared with 88% and 57.1% compared with 35%, respectively)56,59. Similarly, Chan et al. demonstrated that patients undergoing total knee arthroplasty who received a femoral nerve block, either single-injection or continuous, were more likely to achieve 90° of knee flexion by the sixth postoperative day (77% compared with 59%)60. Early physiotherapy and walking are associated with a reduced risk of infection, venous thromboembolism, and arthrofibrosis, the 3 most common causes of hospital readmission following total knee arthroplasty5.
Grevstad et al., in a prospective, randomized, placebo-controlled study, compared quadriceps strength following total knee arthroplasty in 50 patients who received either a femoral or adductor canal block for postoperative pain61. Quadriceps strength was measured immediately prior to and immediately following placement of the block. After the block, quadriceps strength in the femoral-nerve-block group decreased to 16% of the baseline pre-block value. Conversely, the adductor-canal-block group experienced an increase in strength to 193% of the pre-block value. The majority of reviewed studies demonstrated similar pain relief with adductor canal and femoral nerve blocks for surgery about the knee61-63.
Luo et al., in a retrospective review of the effects of femoral nerve block in pediatric patients undergoing ACL reconstruction, reported a substantial isokinetic strength deficit for both flexion and extension at 6 months after surgery64. Sixty-seven percent of pediatric patients who were managed with a femoral nerve block met strength criteria for return to play at 6 months, compared with 90% of those in the control (no-block) group.
Length of Stay
The benefit of a peripheral nerve block in shortening length of stay after major knee surgery is unclear. The recent literature has been divided and inconclusive at best. In a review of 1,768 patients undergoing total knee arthroplasty, Liu et al. noted a shortened length of stay for patients who received both femoral and sciatic nerve block compared those who received systemic analgesia alone (3.61 compared with 3.76 days)59. Wang et al. found a more substantial difference, reporting a stay of 3 days for patients who received a femoral nerve block following arthroplasty, compared with 4 days for those who received no block65. Hebl et al., in a retrospective study, reported an average length of stay of 3.8 days for patients who received regional anesthesia, compared with 5.0 days for those who received PCA alone56. Schloss et al., in a retrospective study of 376 pediatric patients undergoing arthroscopic knee surgery who required hospital admission, reported a 4-hour decrease in the length of stay when patients who received a femoral nerve block were compared with those who received local periarticular infiltration (11.7 compared with 15.8 hours)57. Patients in that study who underwent ACL reconstruction and received a femoral block also had a lower admission rate when compared with those who did not receive a femoral nerve block (72% compared with 95%). In contrast to the above data, 3 large prospective randomized trials in which a combination of regional anesthesia and systemic analgesia was compared with systemic analgesia alone failed to show any significant difference in length of stay following total knee arthroplasty or ACL reconstruction6,66,67.
In a large retrospective Medicare database analysis, patients who were managed with femoral nerve block had lower rates of hospital readmission at 30, 90, and 365 days after total knee arthroplasty5. In addition, they had fewer episodes of dislocation at 30 and 90 days. There was an increased risk of revision at 30 days and a slight increase in stiffness up to 1 year in the block group. The revision rate was unexplained in that study as the rates of infection, wound complications, and mechanical complications were not increased, and the dislocation rate was decreased in the block group. The authors postulated that increased early stiffness may have been due to prolonged strength deficits in the femoral nerve block group, although they had no evidence for this.
Peripheral nerve block (e.g., femoral nerve block, adductor canal block) is commonly used to provide perioperative analgesia for patients undergoing surgery about the knee. Its many benefits include a decrease in pain and narcotic use, increased participation in postoperative physical therapy, and decreased length of hospital stay. Although there are risks associated with peripheral nerve block by means of single injection or catheter placement, these risks are relatively low. Nerve block in patients managed with total knee arthroplasty is recommended as the benefits substantially outweigh the risks. The use of a nerve block is less beneficial for patients undergoing simple knee arthroscopy (e.g., partial meniscectomy); however, patients undergoing more complex arthroscopic knee procedures (e.g., ACL reconstruction or multiligamentous knee reconstruction) may benefit considerably. In adolescent patients undergoing ACL reconstruction, the potential for pain control should be weighed against the risk of decreased isokinetic strength. If utilized in the properly selected patient, regional anesthesia is an effective technique for providing perioperative pain control for patients undergoing complex arthroscopic knee surgery or total knee arthroplasty.
Investigation performed at the Departments of Orthopaedic Surgery and Anesthesiology & Perioperative Medicine, Drexel University College of Medicine, Hahnemann University Hospital, Philadelphia, Pennsylvania
Disclosure: No external funds were received in support of this study. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article.
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