Introduction
Foot and ankle surgery is increasingly performed in a same-day, outpatient setting but is associated with moderate to severe postoperative pain which may lead to prolonged post-anesthesia care unit (PACU) stay, unanticipated admission and decreased patient satisfaction [
1‐
3]. Postoperative pain was one of the most common reasons for unanticipated admission, in which 57.6% of them were orthopaedic patients [
4]. This moderate to severe postoperative pain following foot and ankle surgery can persist up to postoperative day 3 [
5], which single-injection popliteal sciatic nerve block may not be adequate to manage the pain [
6]. Therefore, continuous popliteal sciatic nerve block (CPSNB) has been developed as a potential pain management method. Several randomized controlled trials have been conducted to compare the efficacy and complications of CPSNB versus single-injection nerve block [
7‐
11]. Some studies concluded that CPSNB was more effective in pain management than the single-injection nerve block [
7,
9‐
11], while Elliot et al. suggested that it was still debatable whether the additional benefits of CPSNB are worthy of its extra time and cost involved because the pain scores were very low in both groups [
8]. Therefore, the first aim of this meta-analysis was to determine the efficacy of CPSNB compared with single-injection group, as a postoperative pain management in patients who had undergone foot and ankle surgery.
In addition to the efficacy, safety concerns are another important issue that should be validated. Neuropathic symptoms and infection following the nerve block are two major complications mentioned in current literature [
12‐
16]. The incidence of neuropathic symptoms after CPSNB has been reported in some studies to be relatively low [
13,
15], but recent studies found a higher rate [
16‐
18]. Other complications including accidental falls, adverse drug reaction and other minor complications associated with the infusion system were also mentioned [
7‐
11,
19]. Thus the second aim of this meta-analysis was to assess the safety of CPSNB and to identify major and minor complications associated with CPSNB.
Discussion
In this meta-analysis, we focused on the efficacy of CPSNB compared with that of single-injection popliteal sciatic nerve block in outpatient foot and ankle surgery. We included 5 RCTs with 208 patients. In comparison with the single-injection nerve block group, patients who received CPSNB presented with less pain (VAS score at 24 and 48 h). Outcome domains including amount of oral analgesics consumed at 72 h, VAS score at 72 h, rate of postoperative admission were considered inconclusive according to the results of trial sequence analysis. There were no major complications including neuropathic symptoms and infection reported in these 5 studies. However, there was a substantial rate of catheter or pump associated complications including catheter dislodge, leakage, irritation, block and pump malfunction.
Effective pain management using regional nerve block as an analgesic adjuvant to anesthesia allows surgeons to perform foot and ankle surgeries as outpatient procedures. Its potential benefits include improved pain control, better patient satisfaction, reduced postoperative opioid consumption and lower costs [
21‐
23]. In the setting of an outpatient procedure, efforts have to be made to prevent unanticipated admissions. In a prospective study of patients who had undergone various ambulatory surgeries, pain was accounted for 12% of unplanned admissions in which 57.6% of them were orthopedic patients [
4]. The analgesic effects of a single-injection nerve blockade is limited to 15–22 h [
6], which might not be adequate to relief severe pain following foot and ankle surgery up to postoperative day 3 [
5]. Therefore, patients might benefit from continuous nerve block to have sustained pain relief.
This study was the first meta-analysis to validate efficacy and safety of CPSNB after foot and ankle surgery as an outpatient procedure, which included five randomized controlled trials for the analysis [
7‐
11]. Compared with the single-injection group, CPSNB was associated with better pain relief up to 48 h. The duration of better pain relief was compatible with the duration of drug administration. In these five studies, a catheter was placed for 48 to 72 h after surgery [
7‐
11]. Difference of VAS score between the continuous and single-injection popliteal sciatic nerve block group might also be diminished as the post-surgical pain decreases with time. In addition, Sutton et al. and Landorf et al. have previously determined the minimal clinical important difference (MCID) of foot and ankle surgeries. The authors determined that a difference in VAS score of 0.8 can be considered the MCID [
24,
25]. In our study, the difference between two groups in VAS score at 24 h and 48 h were 2.28 points and 1.18, respectively. This further confirms that CPSNB resulted in improved pain management in these patients.
Despite the benefits of better pain control and less analgesics consumption, several inherent risks have to be assessed with popliteal sciatic nerve block and the continuous perineural local anesthetic infusion system. Neuropathic symptoms is one of the major complication associated with popliteal sciatic nerve block that raise the concerns [
12‐
14]. Compére et al. prospectively enrolled 400 patients who received CPSNB. Three major complications were reported, including two neuropathies (0.5%) [
13]. Meanwhile, the incidence of neuropathic symptoms after popliteal sciatic nerve block were higher in recent studies [
16‐
18]. Park et al. conducted a retrospective study of 827 patients evaluating the safety of popliteal sciatic nerve block. Twenty-two (2.7%) developed neuropathic symptoms secondary to the nerve block and 7 (0.8%) patients had unresolved symptoms at the final follow-up visit [
17]. The concern of neuropathic symptoms after popliteal block was supported by the results from Anderson et al., a retrospective study of 1014 patients who received single-injection or continuously popliteal sciatic nerve block. One hundred and thirty-five (13.3%) patients developed varying neuropathic symptoms, while most of them (
N = 119, 87.4%) reported exclusively sensory deficits. Of the 99 patients who received a continuous infusion with a catheter, 17 (17.1%) patients developed neuropathic symptoms and 7 (7.0%) of them were likely related to the popliteal block. These neuropathic symptoms required an average of 58.6 days to resolve, while one of them remained unresolved up to 8 months [
18]. In a prospective cohort study conducted by Gartke et al., the incidence of neuropathic symptoms after the CPSNB was even higher as 41% of patients at postoperative 2 weeks and 24% at 34 weeks had persisted symptoms [
16]. Most of the neuropathic symptoms described were sensory deficits of various degrees. The varied incidence of neuropathic symptoms might be due to different study designs (prospective or retrospective data collection), the definition of neuropathic symptoms, and the frequency and duration of follow-up visits [
13,
16‐
18].
Regarding risk factors for neuropathic symptoms, Anderson et al. did not find an association between neuropathic symptoms with smoking, diabetes, tourniquet location or time, use of steroids and/or epinephrine, single or continuous block, and use of ultrasound or nerve stimulator. There was a younger average age in patients who had neuropathic symptoms (47.3 ± 15 years vs. 50.2 ± 17.2 years,
P = 0.039), compared with those who did not. A higher average tourniquet pressure was found in patients who had neuropathic symptoms (309.4 ± 28.9 mmHg vs. 303.4 ± 24.9 mmHg,
P = 0.013). Although a statistical significance was noted, the authors suggested that this difference might have minimal clinical significance. Gartke et al. found that smoking history was a borderline significant factor for developing neuropathic symptoms (adjusted OR: 2.25, 95% CI: 0.96–5.33). The authors did not find tourniquet time, tourniquet application site, experience of the specialist performing the block, use of prophylactic antibiotics, and type of anesthesia to be associated with neuropathic symptoms. Although the exact mechanism causing these neuropathic symptoms remain controversial, some authors have hypothesized that some anesthetics may be directly toxic to nerve fibers [
26‐
28]. Local anesthetics including ropivacaine and bupivacaine block impulse conduction in nerve fibers through inhibition of both sodium ion and potassium ion channels [
29]. In addition, the concentration and duration of local anesthetics have been shown to contribute to chemical neurotoxicity in an animal model [
27]. Increased amount of anesthetics was associated with an elevated intrafascicular pressure that exceeds the nerve capillary perfusion pressure, which would lead to ischemic injury. On the other hand, drugs administered along with the anesthetics such as epinephrine can have a local vasoconstrictive effect that potentially aggravates the ischemic injury [
16,
18,
26,
28]. Despite these hypothesis, there are no clinical studies to validate the relationship between the use of common local anesthetics or epinephrine and postoperative neuropathic symptoms. Therefore, studies with high level of evidence are warranted to validate the safety of corticosteroids, epinephrine and each anesthetic. For patients with a smoking history or pre-existing neuropathies, an alternative pain control method to CPSNB should be considered to avoid postoperative neuropathic symptoms.
In the 5 RCTs included in this meta-analysis, Elliot et al. reported a patient in the placebo group who experienced numbness on the dorsal foot which resolved after 5 days [
8]. White et al. found a higher incidence of “tingling sensation” on the foot in the CPSNB group (80% versus 10% in the placebo group) [
10]. The duration of this sensation was not described. Anderson et al. defined abnormal postoperative neuropathic symptoms as burning, pain, numbness, or tingling in the operative limb that persisted for at least 7 days following a single injection or after catheter removal for continuous infusions. According to this definition, there were no neuropathic events in the 5 studies included in this meta-analysis.
Although no major complications were mentioned in either group, there was a significantly higher rate of minor complications associated with the infusion system, including drug leakage, catheter dislodge, pump malfunction and catheter blockade. When using a portable infusion system, patients have to take an extra responsibility that comes with the device. Those minor complications might lead to a significant rate of nonscheduled contact with the physician (
N = 9 of 30, 30%) [
11] and might affect the overall satisfaction rate. A prudent assessment of patients’ desire and a comprehensive verbal and written instruction would be warranted.
There are several limitations that should be recognized. First, the small sample size and a high heterogeneity of clinical settings between studies, including age, gender, doses and regimens used in CPSNB, surgical approaches, catheter locations and types of anesthesia may effect the results, which should be interpreted with caution. Second, we searched only for English articles but not articles in other languages or unpublished data. This might be a potential source for publication bias. Third, there was an inherent flawed setting in these studies that compared CPSNB with the placebo group. A potential bias associated with a “wash out” effect existed in the placebo group. Continuous saline infusion in the placebo group might have diluted the initial, single-injection regional block and shortened the duration. This can lead to a bias toward the efficacy of CPSNB [
11]. Finally, several important outcome parameters with regard to safety concerns of CPSNB including neuropathic symptoms and infection could not be evaluated in our meta-analysis because 4 of 5 RCTs enrolled in this meta-analysis have placed a catheter with saline infusion in the single-injection group to enable blinding of patients. Thus we are unable to present comparative results of major and minor complications between CPSNB and single-injection group but rather an overall descriptive data. Therefore, future studies can be designed to place an emphasis in determining the incidence difference of complications between CPSNB and single-injection to provide a more comprehensive result.
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