FormalPara Key Summary Points

For patients undergoing knee arthroscopy (KA), postoperative pain is a common and troublesome problem. This prospective trial aimed to observe whether adductor canal block (ACB) combined with local infiltration analgesia (LIA) could further decrease the incidence of postoperative pain undergoing KA. We found that ACB combined with LIA could reduce the incidence of postoperative pain at 24 h after surgery in patients undergoing KA, while retaining the strength of quadriceps femoris. This combined analgesic method also significantly reduced the consumption of opioids during surgery.

 

Introduction

Postoperative pain management plays a central role in the postoperative recovery of patients. Inadequate postoperative pain control increases postoperative stress response, postoperative opioid use, and the incidence of postoperative chronic pain. Knee arthroscopy (KA) is the most common outpatient orthopedic surgery performed in the United States, with approximately 1 million procedures performed annually [1]. In a study of opioid use after low-risk surgery, it was found that between 2004 and 2012, 79–82% of patients undergoing KA received opioids after surgery [2]. It is clear that increased opioid use is associated with poorer outcomes. Several investigators were working on nonopioid pain management in patients undergoing KA. Daniels et al. used ibuprofen or acetaminophen to control postoperative pain in patients undergoing KA and found that about 82% of patients can effectively relieve postoperative pain by using the above non-opioid drugs [3].

As an important component of multimodal postoperative analgesia, the local analgesia technique has also been widely used in patients undergoing KA. As previously described in the literature, the main techniques used include peripheral nerve block and local infiltration analgesia (LIA). A systematic review has demonstrated that LIA reduced opioid consumption and pain scores within 24 h of surgery in patients undergoing anterior cruciate ligament reconstruction (ACLR) surgery compared to controls [4]. Femoral nerve block (FNB) has been considered a routine analgesia after KA in the past, however, there is still controversy about its analgesic effect [5, 6]. It is also believed to impair quadriceps muscle strength and has adverse effects on the postoperative mobility of patients undergoing such surgery. Adductor canal blocks (ACB) have been widely used in recent years due to their advantages in providing postoperative analgesia while preserving motor function in patients undergoing KA. Compared to FNB, ACB prevents falls and promotes early postoperative ambulation, which is desirable in ambulatory KA [7]. Nonetheless, current studies on the analgesic effect of ACB in KA surgery have drawn conflicting conclusions [8, 9]. The question of whether all patients should receive LIA or ACB combined with LIA to improve postoperative pain is not fully researched.

We designed this trial to explore whether ACB combined with LIA could further reduce the incidence of postoperative pain in KA patients under general anesthesia compared with LIA alone. We also recorded the incidence of postoperative quadriceps muscle weakness in the two groups.

Methods

Study Design

A single-center, randomized, controlled study was conducted in the First Affiliated Hospital of Anhui Medical University. The study was approved by the Ethics Committee of the First Affiliated Hospital of Anhui Medical University on July 6, 2018 (PJ2018-07-03). The study was registered in Chinese Clinical Trial Registry (ChiCTR1800018463) on September 20, 2018. The study protocol was in accordance with the Declaration of Helsinki.

After obtaining written informed consent from all subjects, patients aged 18–65 years, American Society of Anesthesiologists (ASA) I–II, and received elective anterior cruciate ligament reconstruction (ACLR) surgery under KA were screened. Patients with contraindications for ACB, such as coagulopathy, infection at the puncture site, local anesthetic allergy, and peripheral neuropathy, or a history of chronic opioid use and alcohol or drug abuse and mental illness, such as schizophrenia, anxiety, and depression were excluded in this study.

Randomization and Masking

The random sequence was generated by a computer program and then it was placed in opaque, sealed envelopes. The blind method was not applied to the assistant who checked the effectiveness of ACB. Researchers, anesthesiologists, patients, nurses in the post-anesthesia care unit (PACU) or ward, and postoperative follow-up evaluators all implemented the blind method without knowing about the grouping.

Patients were randomly divided into two groups (ACB + LIA group or the LIA group) in a 1:1 ratio. In the ACB + LIA group, patients received ultrasound-guided ACB (15 ml of 0.375% ropivacaine). In the LIA group, patients received ultrasound-guided ACB (15 ml normal saline) before the induction of general anesthesia, then the local anesthetic (40 ml of 0.25% ropivacaine) was used for periarticular infiltration analgesia in both groups before suturing the incision.

Study Treatments

After the patients were transferred to the operating room, standard monitoring, including five-lead electrocardiogram, noninvasive blood pressure at 5-min intervals, arterial oxygen saturation, bispectral index (BIS), and end-tidal carbon dioxide monitoring were used throughout the surgery.

Before the induction of general anesthesia, patients in the ACB + LIA group received ultrasound-guided ACB: (1) Position: Patients were kept supine for ACB. (2) Method: A 5-cm, 10-MHz linear probe (M-Turbo; FUJIFILM Sonosite Inc., Bothell, WA, USA) was used in this study [10]. The probe was placed at the mid-thigh level and slid on the inner thigh, about halfway between the anterior superior iliac spine and the superior border of the patella. Then the superficial femoral artery and its anterolateral hyperechoic structure, saphenous nerve, and sartorius muscle were identified. A 12-cm, 22-gauge insulated needle (Stimuplex D; B. Braun Medical Inc.) was inserted using the in-plane technique from the lateral direction. The needle was slowly advanced until the needle tip reached below the sartorius muscle, and the lateral border of the superficial femoral artery, the position of the needle tip was confirmed using a hydrodissection technique [11]. After negative aspiration of blood, 15 ml of 0.375% ropivacaine was injected. (3) Technician: The ACB procedure was performed by anesthesiologists with over 5 years of experience. (4) Assessment: The effectiveness of the block was checked by an assistant 10 min after completion of the ACB procedure. A diminished or absent sensation of the pinprick test was considered as block success. After the completion of the blocks and the assessments for block success, patients were then transferred to theatre for surgery under general anesthesia. Nerve block of all patients in the ACB + LIA group has been successful.

All participants received a standardized anesthesia protocol. Anesthesia was induced with etomidate (0.2–0.3 mg/kg), sufentanil (0.4 μg/kg), and cisatracurium (0.2 mg/kg). Then a laryngeal mask airway was inserted after 5 min. Mechanical ventilation was initiated and adjusted so that end-tidal carbon dioxide could fluctuate between 35 and 45 mmHg. Remifentanil (0.2–0.5 μg/kg/min) and the target-controlled infusion of propofol (1.0–4.0 μg/ml) were adopted for anesthesia maintenance. The target BIS value was set at 40–60. Intraoperative inadequate analgesia was defined as blood pressure or heart rate 20% higher than baseline, and then the infusion rate of remifentanil would be increased. Sufentanil (5–10 µg) was intermittently administered during the whole operation process to maintain the fluctuation of heart rate and blood pressure within 20% of the baseline level. Propofol and remifentanil infusions were stopped 5 min before the end of surgery.

All patients in the two groups were treated with periarticular LIA by the surgeon before the incision was sutured [12]. The method of LIA was that 40 ml of 0.25% ropivacaine was injected in the empty space created after harvest of the gracilis and semitendinosus tendons, in the iliotibial band through the surgical exposure used for femoral tunnel drilling, and for extra-articular tenodesis and in the subcutaneous tissue. After the operation, when the spontaneous breathing of patients was regular, the tidal volume > 6 ml/kg, and SpO2 > 95%, the laryngeal mask was pulled out. The patients were then transported to post-anesthesia care unit (PACU).

All patients received a standard postoperative analgesia regimen, and for the first 3 days after surgery, all patients received flurbiprofen-axetil (100 mg) intravenously every 12 h. A single remedial dose of tramadol (50–100 mg) was used as needed in the ward.

Outcomes

The study personnel carefully recorded the relevant baseline characteristics and perioperative data of the patients. The primary outcome was the incidence of postoperative pain 24 h after surgery. In the first 24 h after surgery, all patients were asked to evaluate their pain intensity evoked by 60 degrees of passive knee flexion. We used the visual analogue scale (VAS) to evaluate the degree of postoperative pain. A VAS score ≥ 4 was defined as moderate-to-severe pain. Patients were asked to rate their pain intensity as mild or moderate-to-severe. Patients who answered moderate-to-severe pain were considered to have postoperative pain. The secondary outcomes were the incidence of postoperative quadriceps weakness at 24 h after surgery, intraoperative consumption of opioids, duration of anesthesia and surgery, recovery time, the duration of PACU stay, and extubation time. Oxford muscle strength grading was used to measure postoperative quadriceps strength, and scores were grouped as intact (5/5), reduced (1–4/5), and absent (0/5). We defined scores (0–4/5) as weakness [13]. Recovery time was defined as the time from the end of surgery to the patient’s consciousness recovery and extubation time was defined as the time from the end of surgery to the removal of laryngeal mask. If patients did not leave the hospital within 24 h after the operation, the postoperative follow-up would be measured in the ward. If patients were at home 24 h after surgery, then they would record the pain assessment by telephone.

Statistical Analysis

Based on data from the pilot study, seven patients in LIA group reported postoperative pain and two patients in ACB + LIA group reported postoperative pain at 24 h after surgery. A 20% reduction in the incidence of postoperative pain was considered clinically significant. Therefore, 26 patients were required in each group, with an alpha level of 0.05 and a power of 80%. A 10% drop-out rate was allowed, and 30 patients per group were considered enrolled.

Continuous variables were presented as mean ± standard deviation (SD) or medians (inter-quartile range, IQR). Categorical variables were expressed as numbers (percentage). Continuous data were compared using an independent samples t test and Mann–Whitney U test as appropriate. Categorical data were compared using Pearson’s chi-square test or Fisher’s exact test as appropriate. Based on the two-tailed probability, significance was considered when P < 0.05. All statistical analyses were done using SPSS 16.0 (IBM Corp., Armonk, NY, USA).

Results

A total of 86 patients scheduled for elective KA surgery were assessed for study eligibility from October 2018 to January 2020, and 26 of them were excluded: 19 patients did not meet the inclusion criteria and seven patients refused to participate. The remaining 60 patients were randomly assigned to the ACB + LIA group (n = 30) and the LIA group (n = 30). No patients in either group dropped out of the study, and 60 patients were included in the final analysis (Fig. 1).

Fig. 1
figure 1

CONSORT flow diagram for this study. This flow diagram shows a single-center, randomized, controlled trial in patients undergoing knee arthroscopy from October 2018 to January 2020. In the ACB + LIA group, patients received ultrasound-guided ACB (15 ml of 0.375% ropivacaine) before the induction of general anesthesia, then the local anesthetic (40 ml of 0.25% ropivacaine) was used for periarticular infiltration analgesia before suturing the incision. In the LIA group, patients received ultrasound-guided ACB (15 ml of normal saline) before the induction of general anesthesia, then the same dose of local anesthetic for infiltration analgesia at the same time. ACB + LIA adductor canal block + local infiltration analgesia, LIA local infiltration analgesia

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The baseline data, including age, ASA, BMI, and sex, showed no significant differences between the two groups. There was also no significant difference in the duration of surgery and anesthesia between the two groups (Table 1).

Table 1 Patient baseline characteristics and intraoperative variables
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Outcomes

The incidence of postoperative pain 24 h after surgery in the ACB + LIA group was significantly lower than the LIA group (10% [3 of 30] vs. 33% [10 of 30]; P = 0.028), and there was no significant difference in the incidence of quadriceps muscle weakness 24 h after surgery between the two groups (13% [4 of 30] vs. 7% [2 of 30]; P = 0.667) (Table 2).

Table 2 Intraoperative anesthetics and postoperative data
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Both the intraoperative consumption of remifentanil and sufentanil in the ACB + LIA group was significantly lower than the LIA group (P = 0.006, P < 0.001). No significant difference was found in intraoperative consumption of propofol. No significant difference was found in the recovery time or extubation time. The duration of PACU stay in the ACB + LIA group was significantly shorter than the LIA group (P = 0.023) (Table 2). No adverse reactions related to local anesthetics were observed in patients throughout the study. No regional nerve block complications such as peripheral nerve injury, hematoma, local anesthetic systemic toxicity, or falls were documented (Fig. 2).

Fig. 2
figure 2

Anatomical landmarks for performing the adductor canal block. This figure shows the anatomical location of the ultrasound-guided adductor canal block. The arrow points to the adductor canal. VM vastus medialis, SM sartorius muscle, FA femoral artery, L lateral, M medial

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Discussion

This study showed that ACB combined with LIA in patients undergoing KA had a lower incidence of postoperative pain 24 h after surgery and lower intraoperative consumption of opioids compared with patients receiving LIA alone. Moreover, ACB did not increase the incidence of quadriceps femoris weakness.

Whether the local analgesia technique is the superior choice for patients undergoing KA is still unknown. As far as the three widely used local analgesic techniques are concerned, ACB, LIA, and FNB are controversial in their postoperative analgesic effects on patients undergoing KA. As the two main peripheral nerve block techniques used in KA, both FNB and ACB have been used for postoperative pain relief with a certain history [14]. However, its highly effective analgesic effect must be balanced against its limitations, including motor block and muscle hypofunction. Quadriceps muscle strength is critical for patients undergoing KA who require early and safe ambulation after surgery. ACB as an alternative to FNB can block only the saphenous nerve, resulting in less quadriceps weakness [10]. Similarly, LIA is a simple technique that provides effective pain relief for knee surgery through intra-articular injection of the local anesthetic. The mechanism of LIA in KA patients can be summarized as follows: Firstly, local anesthetics are directly applied to the nerve terminal branches, innervating the surgical area. LIA is easier to operate than blocking the individual nerves that innervate the surgical area, such as the femoral nerve, the common peroneal nerve, and the posterior tibial nerve. Secondly, local anesthetics also act on peripheral opioid receptors present in tissues [15]. A recent meta-analysis involving 11 randomized controlled trials concluded that LIA reduced pain scores and opioid consumption 24 h after surgery in patients undergoing ACLR [4]. Abdallah et al. recommended the use of LIA in combination with non-opioid multimodal analgesia for pain control after outpatient ACLR (strong recommendation, moderate level of evidence) [16]. Therefore, surgeons should be encouraged to perform LIA whenever possible in clinical practice. However, the authors left open the question of whether the combination of LIA and peripheral nerve block in KA patients would yield greater benefits. That is what motivated the present authors to do this experiment. In our study, we found that the additional ACB in patients receiving KA effectively reduced the incidence of moderate-to-severe postoperative pain without compromising quadriceps muscle strength.

The adductor canal consistently contains the saphenous nerve, the nerve to the vastus medialis. The above nerves contribute to substantial innervation to the anteromedial aspect of the knee joint, including the joint capsule and the medial retinaculum [17]. The anatomical basis of ACB makes it possible to apply this approach to KA patients. Several studies have confirmed that ACB could reduce pain scores and postoperative opioid consumption 24 h after surgery [8, 18, 19]. A meta-analysis including ten randomized trials of ACB concluded that ACB could provide modest analgesia and reduce postoperative opioids consumption during minor KA surgery. However, the performance of ACB in ACLR was summarized, as no additional analgesic effect compared with placebo. The authors were cautious about this result due to the small number of studies included and expect more trials in the future to confirm the results [20]. Previous studies have also investigated the analgesic effects of ACB combined with LIA in total knee arthroplasty (TKA) [21, 22]. Agarwala et al. reported that ACB combined with LIA could significantly reduce postoperative 24-h pain scores, but are not clinically relevant [21]. In this study, all patients received spinal anesthesia and the intraoperative opioid-free effect of ACB was erased, unlike in our study. The LIA mixtures used in the study included local anesthetics, nonsteroidal anti-inflammatory drugs, and opioids. The analgesic efficacy of these LIA components might be different from that of our study, leading to different conclusions. Therefore, the introduction of ACB into postoperative analgesia in KA patients still has potential clinical significance. In an era plagued by opioid abuse and chronic dependence, and with the growing evidence of widespread opioid use after major surgery, the use of non-opioid techniques to improve postoperative patient pain cannot be overemphasized [23, 24]. In a relatively young and generally healthy population with KA, a small benefit from postoperative analgesic intervention might lead to a greater benefit [25]. Since ACB might be clinically relevant in KA patients, it is feasible to add it to postoperative multimodal pain management protocols in KA patients.

Several limitations should be mentioned in our study. Firstly, although other researchers have used adjuvants including non-steroidal anti-inflammatory drugs and opioids, no consensus has been reached on the ideal drug regimen for LIA. Therefore, LIA in our study only included local anesthetics without adjuvant. Secondly, in our study, the method to test the success rate of the block after ACB implementation might lack certain objectivity, more accurate instruments and clinical evaluation criteria should be further used to evaluate this blocking effect.

Conclusions

Compared with simple local infiltration analgesia, the addition of an adductor canal block under the premise of local infiltration analgesia can reduce the incidence of postoperative pain in patients undergoing knee arthroscopy, while retaining the strength of the quadriceps femoris.