Among Medicare beneficiaries in the United States, the number of primary total knee arthroplasty (TKA) procedures from 1991 to 2010 increased by 161.5% (1). Postoperative pain remains one of patients’ top concerns when undergoing elective surgery (2) and can limit patients’ functional ability in the early postoperative period (3). Providing effective perioperative pain control has potential longer-term implications since early rehabilitation may lead to improvements in functional outcomes later on (4). With the ability to select specific targets for local anesthetic injection and infusion, regional anesthesia techniques, neuraxial and peripheral, are commonly included in the perioperative analgesic protocol for joint arthroplasty patients (5-11). While the data supporting the analgesic efficacy of regional anesthesia techniques in this setting are strongly positive, studies attempting to attribute functional outcome benefits to regional anesthesia demonstrate mixed results.
The main challenge in assessing functional outcomes following joint replacement is the selection of outcomes; these can be divided into performance-based outcomes and self-reported outcomes (12, 13). Performance-based outcomes are measurable and arguably more objective, although often subject to effort. Examples of these outcomes and their units of measure include joint range of motion in degrees (e.g., flexion, extension, rotation); timed walking tests in meters (e.g., 6 minute walking test [6MWT], 2 minute walking test [2MWT]); muscle strength in units of force using a dynamometer (e.g., maximum voluntary isometric contraction [MVIC]); and timed up-and-go (TUG) in minutes (12, 13). Self-reported outcomes are typically survey-based; examples include the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC), Knee Society Score, and Lower Extremity Functional Scale (12, 13). Since patient perception of successful rehabilitation is an important factor, self-reported outcomes should be reported with performance-based outcomes (12). Another important challenge when measuring and comparing functional outcomes is that clinical pathways for joint arthroplasty that integrate pain management (including regional analgesia), physical therapy, nursing, and surgical care are often specific to individual institutions, and institutions may vary with respect to rehabilitation goals and the timeline to achieve them.
Epidural analgesia has been used for perioperative pain management in joint replacement patients since at least the 1980s (14, 15). In 1987, Raj and colleagues compared postoperative systemic opioid analgesia to continuous epidural analgesia (bupivacaine 0.25% at 6-15 ml/hr) for TKA patients in a prospective non-randomized study (14). Although pain scores were lower in the epidural group, not surprisingly a high proportion of these patients experienced complete motor block of the lower extremities; although the authors mention “rigorous passive exercises,” specific rehabilitation outcomes were not reported (14). Later studies have reported functional benefits associated with continuous epidural analgesia, such as shorter time to achieve ambulation distance and range of motion goals, when compared to parenteral opioids alone (16). At institutions where continuous epidural analgesia is currently employed as part of a multimodal analgesic protocol, very low doses of local anesthetic (e.g., 0.06% bupivacaine) in combination with opioid are used in order to minimize motor block (17).
Peripheral Nerve Blocks
The innervation of the knee is complex and involves contributions from both the lumbar and sacral plexuses. While epidural analgesia is effective, it is also associated with clinically-significant side effects (e.g., nausea/vomiting and motor block of the non-operative limb) (5, 18) and the potential for neuraxial hematoma in patients on pharmacologic thromboprophylaxis (19). Thus, peripheral nerve block options, either single-injection or continuous infusions, have been explored for postoperative pain management.
Two early studies by Capdevila (6) and Singelyn (20) have shown continuous femoral nerve block (FNB) to provide comparable analgesia and physical therapy outcome achievement with fewer side effects when compared to epidural analgesia. Both of these studies also demonstrated shorter hospital length of stay for the regional anesthesia groups compared to an opioid-only group (6, 20), but hospitalization duration for these studies was, on average, greater than what has been reported in other studies (21). Triple-masked, placebo-controlled randomized clinical trials have shown that CPNB can shorten the time to achieve discharge criteria, including 100 m ambulation distance, for TKA (10, 22) and total hip arthroplasty (THA) (9) patients, but actual hospital duration was similar in these studies.
One of the interesting findings from the Singelyn study was that regional anesthesia patients maintained a knee flexion advantage over the opioid-only group at 6 week follow-up (20); although this advantage did not remain at 3 months, this finding supported the potential for long-term functional improvement resulting from effective pain management and early rehabilitation in the immediate perioperative period (4). In a randomized comparison of continuous FNB to local infiltration analgesia (LIA) for TKA, the FNB group spent more time out of bed walking; at 6 weeks, the FNB group showed more improvement in performance-based (6MWT) and self-reported functional outcome assessments (23). In contrast, the one year follow-up studies of randomized clinical trial subjects (9, 10, 22) using self-reported outcome measures for functional status (WOMAC) did not show long-term improvement associated with regional anesthesia techniques (24-27).
The rehabilitation outcome measured in the immediate postoperative period that correlates best with long-term functional improvement is not yet established. Ambulation distance is often measured by physical therapists and included in discharge criteria (9, 10, 22). For institutions that emphasize ambulation in their clinical pathway for lower extremity joint arthroplasty, a major concern raised with regard to FNBs is the potential association with increased fall risk (28, 29) although a recent large database study disputes this finding. In-hospital falls can lead to prolonged hospital stays with higher costs and are associated with more frequent postoperative complications, including serious organ system dysfunction and death (30). With currently-available local anesthetic solutions and typical doses, perineural infusion does produce clinically-significant quadriceps weakness when administered near the femoral nerve or lumbar plexus (31, 32). Since the local anesthetics themselves cannot select sensory over motor nerves( 33), anesthesiologists have started exploring alternate nerve block locations to minimize the risk of motor block and maximize patient rehabilitation.
For TKA, a more distal nerve block location in the adductor canal can provide effective analgesia postoperatively (34) and has been shown to better preserve quadriceps strength compared to a FNB in both volunteers (35) and clinical patients (11). Regional analgesic techniques are only one part of the overall pain management plan. While they are often included in multimodal analgesic protocols along with non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and low-dose opioids (36), there is a growing body of evidence to support the adductor canal block as the regional analgesic technique of choice for promoting postoperative ambulation within a clinical pathway (37, 38).
For patient information with answers to frequently-asked questions about regional anesthesia, please see “Regional Anesthesia FAQs.”
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