3.4 Evidence level
All outcomes in this meta-analysis are evaluated using the GRADE system. The evidence quality for most outcomes is high (Table 4) which means further research is very unlikely to change our confidence in the estimate of effect.
3.5 Outcomes for meta-analysis
3.5.1 NRS scores at rest at POD 0
Four studies with 297 patients show the NRS scores at POD 0 after TKA. A fixed-effects model is used because no significant heterogeneity is found among the studies (χ2 = 2.09, df = 3, I2 = 0%, P = .553). The pooled results demonstrate that NRS scores at POD 0 is significantly higher in the control groups than in the experimental groups (weighted mean difference [WMD] = −0.849, 95% CI: −1.345 to −0.353, P = .001, power = 86%; Fig. 2).
3.5.2 NRS scores at rest at POD 1
Four studies with 297 patients report the outcome of NRS scores at POD 1 after TKA. Significant heterogeneity is detected between groups (χ2 = 8.33, df = 3, I2 = 64.0%, P = .040). There is significant difference in NRS scores at POD 1 between groups (WMD = −0.960, 95% CI: −1.474 to −0.446, P = .000, power = 82%; Fig. 3).
3.5.3 NRS scores at rest at POD 2
Four articles with 297 patients report the outcome of NRS scores at POD 2 after TKA. A fixed-effects model is used because no significant heterogeneity is found among the studies (χ2 = 2.50, df = 3, I2 = 0%, P = .475). There is significant difference in NRS scores at POD 1 between groups (WMD = −0.672, 95% CI: −1.163 to −0.181, P = .007, power = 88%; Fig. 4).
3.5.4 Opioid consumption at POD 0
Opioid consumption at POD 0 is reported in 4 articles. No significant heterogeneity is found among these studies (χ2 = 0.57, df = 3, I2 = 0%, P = .904) and a fixed-effects model is used. A significant difference is detected between the 2 groups (WMD = −3.761, 95% CI: −6.192 to −1.329, P = .002, power = 80%; Fig. 5).
3.5.5 Opioid consumption at POD 1
Four studies with 297 patients show the outcome of opioid consumption at POD 1 after TKA. A fixed-effects model because no significant heterogeneity is found (χ2 = 0.23, df = 3, I2 = 0%, P = .973). There is significant difference in opioid consumption at POD 1 between groups (WMD = −4.795, 95% CI: −8.181 to −1.409, P = .006, power = 83%; Fig. 6).
3.5.6 Opioid consumption at POD 2
Four articles provide the data of opioid consumption at POD 2 after TKA. A fixed-effects model is used because no significant heterogeneity is found (χ2 = 2.46, df = 3, I2 = 0%, P = .482). There is significant difference in opioid consumption at POD 2 between groups (WMD = −2.867, 95% CI: −4.907 to −0.827, P = .006, power = 86%; Fig. 7).
3.5.7 Length of hospital stay (LOS)
Four studies report the lengths of the hospital stay for the groups. No significant difference in the LOS is observed between the 2 groups (WMD = 0.075, 95% CI: −0.020 to 0.169, P = .120, power = 88%; Fig. 8).
Four articles showed the postoperative complications of nausea. A fixed-effects model is used (χ2 = 0.43, df = 3, I2 = 0%, P = .935). Significant difference in the incidence of nausea is found between the 2 groups (RD = −0.121, 95% CI: −0.225 to −0.016, P = .024, power = 90%; Fig. 9).
Four studies report the postoperative complications of vomiting after TKA. A fixed-effects model is used (χ2 = 0.67, df = 3, I2 = 0%, P = .881). The pooled results demonstrate that there is an increased risk of vomiting in control groups (RD = −0.107, 95% CI: −0.203 to −0.012, P = .027, power = 91%; Fig. 10).
Four articles showed the postoperative complications of constipation. A fixed-effects model is used (χ2 = 1.01, df = 3, I2 = 0%, P = .798). Significant difference in the incidence of constipation is found between the 2 groups (RD = −0.134, 95% CI: −0.231 to −0.038, P = .007, power = 90%; Fig. 11).
Four studies report the pruritus for the groups. No significant difference is observed between the 2 groups (RD = −0.047, 95% CI: −0.150 to 0.056, P = .369, power = 93%; Fig. 12).
To the best of our knowledge, this is the first meta-analysis to evaluate the efficiency and safety of the combined adductor canal block with peri-articular infiltration versus periarticular infiltration alone for pain control following TKA. The most important finding of the present meta-analysis is that the combined adductor canal block with peri-articular infiltration can significantly reduce postoperative pain scores and morphine equivalent consumption. Additionally, there is a lower risk of opioid-related adverse effects, such as nausea and vomiting in combined groups. The quality of the evidence for each outcome is high, meaning that further research is unlikely to change confidence in the effect estimate.
As the population ages, the incidence of knee osteoarthritis is increasing. TKA is an excellent surgical procedure for patients with painful arthritic knees. However, TKA is usually associated with moderate to severe postoperative pain. Postoperative pain following TKA is usually intense, and immediate postoperative opioid consumption can be high. A consensus has been reached that effective postoperative analgesia improved patient outcomes by allowing early ambulation and rehabilitation. The optimal analgesic strategy remains controversial and pain control after TKA is an interesting topic in the field of orthopedic surgery. Multimodal pain management following TKA is recommended in order to improve pain relief and reduce opioid consumption.[17,18]
Local infiltration anesthesia is widely performed and shows satisfactory outcomes for pain control following TKA. Song et al reported that peri-articular injections offered improved pain control and minimal side effects in comparison to patient-controlled analgesia. Thus, peri-articular injections can replace conventional PCA for controlling postoperative pain after TKA. Yun et al performed a meta-analysis from RCTs to compare the analgesia achieved with local infiltration anesthesia and femoral nerve block following TKA. They indicated that local infiltration anesthesia may be the optimal choice in pain management of TKA, as it could achieve fast pain relief and was easier to perform than femoral nerve block for patients with TKA. However, local infiltration anesthesia has been criticized by some experts due to its short-term action and inadequate provision of sufficient analgesia to the anterior aspect of the knee. Therefore, multimodal analgesia protocols are recommended to improve pain relief, decrease total perioperative morphine consumption, increase patient satisfaction, and facilitate early mobilization and discharge.
The adductor canal is an aponeurotic tunnel in the middle third of the thigh, extending from the apex of the femoral triangle to the opening in the adductor magnus, the adductor hiatus. Sensory nerves dominating knee joints were located in the adductor canal. Therefore, blocking these sensory nerves could provide analgesia for patients undergoing TKA. Although femoral nerve block has been recognized as the gold standard for pain control after TKA, adductor canal block has recently gained popularity because of the less block-induced motor weakness. Kim et al compared adductor canal block and femoral nerve block for pain management after TKA and found that the comparative effectiveness of pain reduction and opioid consumption. More importantly, adductor canal block was confirmed to have an early sparing of the quadriceps strength with no difference in range of motion. Wang et al conducted a meta-analysis from RCTs and found that adductor canal block was not inferior to femoral nerve block in regards to pain management or morphine consumption, as well as showing better knee mobility. It was superior regarding the sparing of quadriceps strength and faster knee function recovery with a decreased risk of falls. However, single-shot adductor canal blocks are still insufficient in efficacy or duration. Recent clinical trials have demonstrated that adductor canal block is effective as a rescue block when local infiltrative analgesia is insufficient for pain management and the combined adductor canal block and local infiltration anesthesia seem to be associated with further improvement in pain relief. There is, however, a lack of evidence of the combined adductor canal block with peri-articular infiltration versus periarticular infiltration alone for pain control after TKA. Therefore, we performed the present meta-analysis to provide reliable evidence for orthopedists. The NRS scores at POD 0–3 are the primary outcomes assessed in our meta-analysis. The present meta-analysis indicates that the combined adductor canal block with peri-articular infiltration could significantly reduce NRS scores at rest compared with periarticular infiltration alone for pain control following TKA. Due to the limited data of the included studies, we did not analyze the pain score at movement or on weight bearing. More well-designed RCTs are needed for further study.
Additional morphine equivalent is used as a rescue to concomitant pain management. The personal control aspect of PCA and its rapid onset were preferred by patients. In the present meta-analysis, morphine equivalent consumption is considered an objective measure to assess pain. Morphine-related adverse effects including nausea, vomiting, respiratory depression, and pruritus are well known.[26,27] In addition to the side effects, drug dependence is also an important issue. Minimizing the morphine equivalent consumption is vital for early ambulation and rehabilitation. Currently, whether or not the combined adductor canal block with peri-articular infiltration could further reduce opioid consumption is seldom reported and remains controversial. Meta-analysis can combine the results from multiple studies in an effort to increase power, improve estimates of the size of the effect, and to resolve uncertainty when reports disagree. Four studies with 297 patients overall show the outcome of opioid consumption after TKA. The present meta-analysis indicates that the combined adductor canal block with peri-articular infiltration could further decrease opioid consumption for patients undergoing TKA. Considering that only four RCTs are included in our study, more RCTs with a large sample size are required for subsequent research.
Analgesia efficacy is not the only concern when assessing the analgesia of various strategies. Nausea and vomiting are common adverse effects associated with PCA. Reducing opioid consumption can subsequently decrease such complications that contribute to early ambulation and decreased medical costs. The overall incidence of nausea is 38/149 in the combined groups compared with 51/148 in control groups (P = .02). Combined adductor canal block with peri-articular infiltration could significantly reduce the incidence of postoperative complications. However, more RCTs with long term follow-up are still required.
Several potential limitations of this study should be noted. Only 5 RCTs are included, and the sample size is relatively small. Some important outcome parameters, such as range of motion are not fully described and could not be included in the meta-analysis. The methods of blinding were unclear or not described in some included studies which may influence our results. No studies performed an intent to treat analysis. Short-term follow-up may lead to the underestimation of complications. Publication bias is an inherent weakness that exists in all meta-analyses.
Despite the limitations above, this is the first meta-analysis from RCTs to evaluate the efficiency and safety of combined adductor canal block with peri-articular infiltration versus periarticular infiltration alone for pain control following TKA. Higher quality RCTs are required for further research.
Combined adductor canal block with peri-articular infiltration could significantly reduce NRS scores and opioid consumption in comparison with periarticular infiltration alone following TKA. Additionally, there is a lower incidence of nausea and vomiting in the combined groups.
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Keywords:Copyright © 2017 The Authors. Published by Wolters Kluwer Health, Inc. All rights reserved.
adductor canal block; meta-analysis; pain control; peri-articular infiltration; total knee arthroplasty