1. Describe anesthetic options for TKA

The anesthetic options for TKA, with their advantages and disadvantages, appear in Table 19.1.

Regional anesthetic (RA) techniques offer several advantages over GA including better pain control, lower surgical site infections, reduced neuro-endocrine and inflammatory response, improvement in regional blood flow, and prevention of deep vein thrombosis (DVT; 30% vs. 47%) [1]. Spinal anesthesia also reduces operational costs [4], while producing profound muscle relaxation and better operating conditions compared with other techniques. Although systematic reviews describing the benefits of RA have been critiqued for pooling both older and newer practices [3,5], recent database studies also associate neuraxial anesthesia with a reduction in 30-day mortality and major adverse events, including pneumonia, systemic infection, and cardiovascular and cerebrovascular events [5]. This contrasts with reviews not finding advantages with RA, when effective thromboprophylaxis regimens were utilized [6–7]. However, overall clinical evidence is unanimously in favor of regional techniques with regards to pain control, blood loss, and surgical site infections.

The goal of most fast-track arthroplasty protocols is patient readiness for early physiotherapy. Interestingly, it is not postoperative pain, but impaired muscle function that negatively impacts early functional outcomes. Although there is some evidence to suggest early physiotherapy following knee arthroplasty impacts short-term functional outcomes, the effect on long-term outcomes is unknown [8–9]. Both epidural analgesia and continuous femoral nerve blocks are associated with improved early range of motion and maintaining rehabilitation goals [8, 10].

2. Review the analgesic approaches for postoperative pain relief

Postoperative multimodal analgesic regimens following TKA usually include oral agents with RA or local anesthestic (LA) techniques. Pain levels typically peak on the second postoperative day after TKA, and pain is associated with reductions in sleep, mobility, and general activity. Female gender, younger age, increased BMI, preoperative pain at the surgical site, and the preoperative use of opioids, anticonvulsants, or antidepressants have all been found to be predictors of severe pain following TKA [11]. Since TKA itself reduces the quadriceps muscle function by 60 to 80% [12–13] and this is compounded by weakness due to inhibitory neural reflexes, ideally, RA should attempt to further minimize leg weakness while ensuring adequate analgesia [14]. The main analgesic modalities employed following TKA include:

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  Opioid-based analgesia: Opioids may serve as a primary or rescue component for analgesia [15]. The incidence of respiratory depression is greater in opioid-naïve patients, those with extremes of age, and also with increasing doses [16]. Other common opioid-related adverse events include urinary retention, nausea, and pruritis, which may delay recovery and decrease patient satisfaction [17]. Additionally, opioids alone are poor at controlling dynamic pain; therefore a multimodal approach including RA is preferable.

  
  
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  Epidural analgesia: Epidural analgesia is superior to systemic analgesia in the first four to six postoperative hours [18], but the analgesic benefits are lost 18 to 24 hours postoperatively [26]. Epidurals may serve a dual purpose, providing both intraoperative anesthesia and postoperative analgesia. While epidurals may inhibit motor function and therefore interfere with physical therapy, they are superior to systemic analgesia in terms of pain relief, time to ambulation, and achieving goals for range of motion, especially with dilute anesthetic concentrations [19–21].

  
  
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  High-volume local infiltration analgesia (LIA): Local infiltration analgesia has increased in popularity recently for TKA. In 2007, Kerr and Kohan described LIA of the periarticular tissues with a mixture of ropivacaine, ketorolac, and epinephrine [24]. They demonstrated adequate analgesia, allowing 71% of patients to be discharged on postoperative day 1. However, two large recent reviews had conflicting results. Marques et al. [26] noted the benefit of LIA in reducing short-term pain and hospital stay following both total hip arthroplasty (THA) and TKA. Conversely, Andersen et al. [27] did not find any benefit of LIA for THA. Both reviews found LIA more effective than placebo but inferior to epidural, intrathecal opiates, and femoral nerve block. Additionally, liposomal bupivacaine infiltration at clinically acceptable doses shows no benefit for analgesia when compared with bupivacaine HCl [25].

  
  
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  Peripheral nerve blocks: Femoral nerve block (FNB) is the most commonly placed peripheral nerve block (PNB) for postoperative analgesia, with or without a sciatic nerve block. Combinations of femoral, sciatic, obturator, and lumbar plexus blocks have been utilized. Recently, the adductor canal block (ACB) has gained popularity, providing sensory blockade of the saphenous nerve with a lower incidence of quadriceps weakness. Both single-injection and continuous catheter techniques have been used. Although single injections have shown benefits up to 48 hours, continuous catheters provide superior analgesia. The analgesic utility of FNB was compared with patient-controlled analgesia (PCA) in a recent meta-analysis and was deemed superior for both resting and dynamic pain. Femoral nerve blocks also improved patient satisfaction and early rehabilitation scores while decreasing nausea and vomiting [26]. Peripheral nerve blocks provide equivalent analgesia to epidurals; however, the increased risks of contralateral leg weakness and neuraxial hematomas with the use of newer anticoagulants associated with the neuraxial block contribute to the popularity of PNBs.

3. Explain the risks associated with femoral nerve blocks and how can they be minimized

The majority of adverse FNB-related events may be avoided by regularly monitoring the catheter site, following pain scores, and examining pressure points and evaluating leg strength; however, the risk of patient falls merits further discussion (Table 19.2).

About 1.6% of all hospitalized patients fall postoperatively, potentially leading to serious morbidity or mortality [27]. The majority of falls in surgical patients occur on postoperative day 1 or 2 [38]. While a fall incidence of 3.1% has been found in patients with FNBs following TKA [28], recent large-scale studies have shown that the incidence of falls is similar in patients undergoing TKA without femoral blockade [27, 29]. However, lumbar plexus blocks have been associated with an increased fall incidence (0.5–1.7%) when compared to patients without blocks [30]. Reports are conflicting as to whether patient and surgical factors such as multiple comorbidities or complex surgeries affect fall rates [29, 31]. Falls may in part be minimized through the use of dilute LA concentrations and patient education. No single intervention (patient education, bed alarm, alert bracelets, knee immobilizers, or exercise therapies) reduces fall risk; however, strategies incorporating all of these do decrease fall rates [32].