Evaluation of the Adductor Canal Block for Postoperative Pain Control and Early Functional Recovery in Arthroscopic Knee Surgery: A systematic Review and Meta-analysis of Randomized Trials

Rehabilitation and early mobilization are essential for successful knee arthroscopic surgery. Uncontrolled pain can lead to slowed mobilization and delayed rehabilitation. However, effective postoperative pain control has been correlated with improved patient satisfaction, better short term outcomes, and decreased length of hospital stay [1-4]. Numerous analgesia techniques were introduced aiming to minimize systemic narcotic usage which could reduce the incidence of known adverse reactions including tiredness, nausea, respiratory depression, decreased intestinal motility and urinary retention [5]. Continuous epidural analgesia has been widely applied in clinical practice and it has definite effectiveness, and few systemic side effects. However, this procedure still cause hypotension, intestinal obstruction, urinary retention, motor

block, and walk limitation [6]. Femoral nerve block (FNB) was introduced, even though its analgesic effect was comparable to the epidural technique and has a lower incidence of opioidrelated side effects [7,8]. However, unpleasant numbness and decreased quadriceps function frequently occur [5,9,10].
The saphenous nerve is the terminal sensory branch of the femoral nerve. It provides innervations to the skin overlying the medial, anteromedial, and posteromedial parts of the lower leg [11]. Development of ultrasound now allowed saphenous nerve block in the anteromedial thigh with very high success rates [12]. Recent studies [13][14][15][16] demonstrated the superiority of the ACB in preserving quadriceps muscle strength and thereby early mobilization compared to FNB and epidural technique. Therefore, adductor canal block (ACB) has been successfully used recently for postoperative pain control after knee surgery [3,13].
Achieving pain control and quadriceps muscle power preservation is challenging for patient satisfaction, rapid rehabilitation, and decreasing the hospital length of stay. Our aim in this study was to evaluate the effect of the ACB on postoperative pain control, opioid consumption, and quadriceps muscle power in the arthroscopic knee surgery.

Search methods
We searched the databases including PubMed, Cochrane library, Web of Science, Embase, and reference lists of included studies using the following terms: (adductor canal block, saphenous nerve block, Subsartorial nerve block, knee arthroscopy, arthroscopic knee surgery, menisectomy, and anterior cruciate ligament). RCTs were identified until the date of last research on 30 September 2015.

Selection criteria
The inclusion criteria were RCTs which compared the analgesic effect of ACB with saline injection as a placebo in the arthroscopic knee surgery procedures. Andersen HL et al. [17] stated that ACB was equivalent to the midthigh saphenous nerve block; therefore studies compared the saphenous nerve block with placebo were included. We also added studies compared ACB with FNB in the arthroscopic knee surgery. Outcomes included pain score with rest and activity, opioid consumption and quadriceps muscle power.
The pre-specified criteria were used to select the eligible studies by two reviewers (Elazab. A, Al-zahrani. A). Any disagreement between the two reviewers about the selected studies was resolved by consulting a third reviewer (Radwan. M).

Data extraction
Data regarding the publishing date, location of the study, patient characteristics, intervention and outcomes were extracted. The postoperative pain intensity was measured by 10 points visual analogue scale (VAS) at rest and at active knee flexion during the 1 st post-operative 24 hours. When a numerical rating scale (NRS) score was used, it was converted to a VAS score. Data in other forms (i.e. median, interquartile range, and mean ± 95% CI) were converted to mean ± SD according to Cochrane Handbook [18]. Third outcome including postoperative opioid consumption; and fourth outcome including the quadriceps muscle strength.

Study quality
Risk of bias of included studies were assessed independently by two reviewers, with the following items: random sequence generation, allocation concealment, blinding, incomplete outcome data, selective outcome reporting and other sources of bias [18]. Disagreement was resolved by consulting a third reviewer (

Statistical Analysis
Review Manager Software (Revman 5.3, Cochrane Collaboration, Oxford, United Kingdom) was used for the metaanalysis. The continuous variable outcomes VAS pain scores at rest within the 1 st post-operative 24 hours, VAS pain scores with active flexion of the knee within the 1 st post-operative 24 hours, and opioid usage within the 1 st post-operative 24 hours for metaanalysis were presented as mean difference (MD) and with 95 % confidence interval (95 % CI), Heterogeneity among studies was estimated using I 2 statistic and substantial heterogeneity was represented by an I 2 value greater than 50%. In the presence of significant heterogeneity, we used a random effect model; otherwise, we used a fixed effect model. P values less than 0.05 were considered statistically significant (P < 0.05).

Search results and Description of Studies
Among initially identified 58 articles that were searched in the databases, 33 duplicates were excluded by using endnote program and 13 citations were excluded after screening the titles and abstracts. After reading full texts, 2 citations, which did not fulfill inclusion criteria, were excluded. Ten studies with 661 patients fulfilled the inclusion criteria and were included in the analysis [1][2][3][4]12,[19][20][21][22][23] (Figure 1).     Table 1 summarizes the characteristics of the ten included RCTs. The studies were published between 2008 and 2015. The size of the studies ranged from 40 to 128 patients. Eight studies compared ACB, saphenous nerve block, or infrapatellar nerve block with placebo group injected with sterile saline in arthroscopic knee procedures. However, only two studies compared ACB and FNB in the arthroscopic knee surgery. The type of the injected anesthetic material varied among trials. It was ropivacaine 7.5 mg/mL in four studies, ropivacaine 0.5 mg/mL in two studies, 0.25% bupivacaine in two studies, and 0.5% levobupivacaine in two studies. The nerve block procedure was done preoperatively in six trials, and immediately postoperatively in four trials. General anesthesia was used in nine trial, however spinal anesthesia was used only in one trial. The types of surgeries were anterior cruciate ligament reconstruction (ACLR), arthroscopic assisted anterior cruciate ligament repair, menisectomy, meniscal repair, synovial debridement, microfracture and chondroplasty.
All included studies were randomized by randomization list, or computer-generated numbers. Seven studies reported allocation concealment using sealed envelope. All trials were double blind to participants and outcome assessors.

Results of the Meta-Analysis
VAS Score with Rest: Seven studies with 393 arthroscopic knee surgeries assessed VAS score at rest within 24 hours postoperatively [1][2][3][4]19,21,22]. The combined data showed that the ACB had significantly lower pain score than the sham placebo group (Figure 2  Two studies with 168 ACLR studied the VAS score in ACB group compared to FNB group. One of these studies reported no significant difference in the VAS at rest within 24 hours postoperatively between the two groups [12]. However the other study showed that ACB had significantly higher VAS score at 24 hours postoperatively than FNB [23].
VAS Score with Activity: A total of six studies involving 329 arthroscopic knee procedures reported the results of VAS pain score with activity within 24 hours postoperatively [1][2][3]19,21,22]. Meta-analysis showed that ACB had also significantly lower pain score than placebo (

Quadriceps muscle power
Five studies with 375 patients evaluated quadriceps muscle power [3,4,12,19,23]. RCTs that compared ACB with sterile saline injection showed no difference in the muscle power within the 1 st postoperative 24 hours. Studies compared ACB and FNB reported in one study that ACB had significantly less quadriceps muscle weakness than FNB. However, quadriceps muscle power was not compared between groups in the other study.

Subgroup Analysis
Subgroup analysis was done for eight trials based on the type of arthroscopic procedures. Meta-analysis for the menisectomy subgroup showed that the ACB had lower VAS score with rest within 24 hours than placebo (

Discussion
The main findings in this study were; the VAS pain scores at rest and activity were significantly reduced with ACB than placebo within the 1 st postoperative 24 hours. However combined result showed no difference between ACB and placebo in the opioid consumption within the 1 st postoperative 24 hours. Quadriceps muscle strength showed also no difference between ACB and placebo group.
There are several limitations of this study. First, the quadriceps muscle strength outcome was extracted from the involved studies and summarized. However, meta-analysis could not be done due to deficient data. Secondly, the number of RCTs which compare ACB with FNB in the arthroscopic knee surgery was limited and statistical data was not enough for the comparison. Finally, different anesthetic drugs were used with different concentration in the included studies which may affect the result. However, the strength of this analysis that it compared mainly the RCTs which studied the ACB against nonblock control group.
Controlled pain and preserved quadriceps muscle power are essentials for postoperative early mobilization and functional recovery post knee arthroscopic surgery. Previous studies concluded that FNB have been shown to improve postoperative pain analgesia and hospital length of stay than systemic opioid therapy post arthroscopic knee surgery [3,4,[24][25][26][27]. However, FNB had some severe side effects, such as reducing quadriceps muscle strength, delayed mobilization and being associated with the risk of falling [28,29]. These complications could be prevented with ACB as a pure sensory nerve block sparing the motor fibers of the femoral nerve and subsequently preserving the quadriceps muscle power [30][31][32].
Akkaya et al. [3] and Hanson et al. [2] studied the effect of saphenous nerve block on postoperative pain control post menisectomy compared to placebo. They concluded that ACB decrease the pain score significantly at rest and activity in addition to improving patient comfort post-surgery. In these studies, opioid consumption was also significantly reduced with ACB than placebo. Hanson et al. [2] stated that all patients in both groups were able to stand in the post anesthesia care unit and no study participant subjectively mentioned leg weakness or reported falls within postoperative 24 hours. However, they didn't objectively measure the quadriceps muscle strength.
Lundblad et al. [1] compared the infrapatellar nerve block and placebo for the arthroscopy assisted ACL repair. They stated that it could improve pain and increase the number of sleep hours if it is included in a multimodal analgesic approach. Espelund et al. [21] compared the ACB and placebo for ACLR in another study. They reported that basic analgesic regimen with paracetamol, ibuprofen, and opioid were acceptable and ACB was not warranted.
Chisholm et al. [12] and El Ahl [23] compared the ACB with the FNB post ACLR. Chisholm et al. [12] stated that there were no significant difference between the two groups in pain score at rest, and opioid consumption within postoperative 24 hours. However, they were in doubt about the causes of quadriceps muscle weakness in their study and they attribute it to the FNB or the original injury, therefore, they recommend assessing quadriceps muscle over six or nine month follow up in another study. In the other study, El Ahl [23] concluded that in spite of significant preservation to the quadriceps muscle power in the ACB group than FNB group, the VAS pain score and opioid consumption was significantly higher in the ACB group.
Espelund et al. [20,22] in two different studies compared the ACB and placebo, one study in the minor arthroscopic surgery and the other for postoperative moderate and severe pain after arthroscopic knee surgery. They concluded that there were no significant analgesic effect of the ACB could be detected after minor arthroscopic knee surgery with a basic analgesic regimen. However, the ACB was highly reproducible and low risk option in treating patient with significant pain after arthroscopic knee surgery.
Hsu et al. [4] studied the effect of Infrapatellar saphenous nerve block with 10 ml 0.25% bupivacaine compared with 10 ml isotonic saline on the postoperative pain score, opioid consumption, mobility, discharge time and Lysholm knee score. They reported that no adverse effects or increased quadriceps weakness were observed following use of the nerve block. And they recorded significant improvement in early pain score and twelve-week Lysholm knee score. In another study saphenous nerve block was compared with placebo for postoperative pain control after day-case knee arthroscopy and the statistical result showed no differences in pain at rest, opioid consumption or function between groups [19].
After interpretation of the data included in the previous studies we found that the ACB was introduced as effective method for postoperative pain control and both the VAS score at rest and activity were significantly decreased. Moreover, the most attractive in this technique for the knee surgeons is the selective sensory nerve block while sparing the motor fibers. This could explain the superiority of the ACB over the FNB in preserving the quadriceps muscle power which is critical for early rehabilitation and decreasing the risk of fall post arthroscopic knee surgery.

Conclusion
The ACB in arthroscopic knee surgery could achieve the goals of postoperative pain control and quadriceps muscle power preservation which are essentials for early functional recovery. However, more RCTs may be needed to confirm the efficacy of the ACB and the possibility to replace the FNB for postoperative pain control in the arthroscopic knee procedures.