STRENGTHS AND LIMITATIONS OF THIS STUDY

This study is the first randomised controlled trial of pectineus muscle plane block for postoperative analgesia and early recovery after knee surgery.

This study will provide new options for postoperative analgesia after knee surgery.

Standard perioperative analgesic treatments will be administered to both groups.

The sample size is small.

This study is not a multicentre randomised trial.

Introduction

Effective pain management is crucial for supporting patients during the early stages of recovery after knee surgery.1 Peripheral nerve blocks are commonly employed to relieve pain and to minimise reliance on opioids as well as the risk of adverse effects associated with opioid use. To mitigate postoperative pain following knee surgery, femoral nerve block (FNB) is often used. Notably, FNB can lead to quadriceps weakness2 3 and an increased risk of postoperative falls.4 5

Previous studies have shown that pectineus muscle plane (PMP) blockade can block both the obturator and saphenous nerves.6 The obturator and saphenous nerves are primarily sensory nerves. According to a cadaveric study, the femoral nerve, not the obturator nerve, innervates each of the components of the quadriceps femoris muscle group.7 In comparison to FNB, PMP block may reduce the risk of postoperative falls and better preserve quadriceps strength and mobility.7 A study involving healthy volunteers revealed that FNB decreased quadriceps strength by 49% from baseline.3 It has been shown that adductor canal block (ACB) can also effectively relieve pain after total knee arthroplasty, but the blockade primarily affects the saphenous nerve. Two retrospective cohort studies8 9 have shown that the analgesic effect of ACB is comparable to that of FNB. PMP block may provide better analgesic effects than FNB and ACB; however, no research exists on the use of PMP block for analgesia after knee surgery. Currently, the postoperative analgesic demands for knee surgery patients are inadequately met by long-acting local anaesthetics such as ropivacaine, which only provide relief for 6 hours.10 11 Continuous delivery of local anaesthetics through a peripheral nerve catheter can extend analgesia, but this approach has drawbacks, including catheter displacement and increased infection risk.12 13 According to some research,14 15 long-acting glucocorticoids, such as dexamethasone, can extend the duration of sensory and motor blockages in peripheral nerves. Zeng et al 16 reported that local anaesthetics combined with dexamethasone prolong the duration of nerve block and decrease the Visual Analog Scale (VAS) Score at rest as well as pain severity at 48 hours after surgery.

Therefore, we have designed an open, randomised controlled trial to demonstrate the effectiveness of PMP block as a new blocking technique for postoperative analgesia in knee surgery patients, as well as the addition of dexamethasone to local anaesthetics to prolong analgesia. The goal of this study is to provide evidence that blocking the PMP enhances analgesia, encourages rapid rehabilitation and shortens the length of hospital stay.

MethodsStudy design and setting

The trial was approved by the relevant hospital’s ethics committee. Informed consent will be obtained from each participant involved in the study, a process previously sanctioned by the Ethics Council of Zhejiang Hospital.

This trial began in October 2023 and is scheduled to conclude in June 2024, and the current focus is on recruiting prospective participants from among hospitalised knee surgery patients at Zhejiang Hospital. The first patient was enrolled on 1 October 2023. The anaesthesiologists will invite eligible individuals to participate in a preoperative consultation. The inclusion and exclusion criteria, as illustrated in figure 1, will be applied during the participant screening process. Patients who meet the inclusion criteria and do not meet any exclusion criteria will be considered eligible for randomisation. This study will adhere to the Consolidated Standards of Reporting Trials guidelines17 as well as the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) guidelines.18 Online additional file 1 contains the SPIRIT 2013 Checklist.

Figure 1

Flow diagram of study design. FNB, femoral nerve block; PCA, patient-controlled analgesia; PMP, pectineus muscle plane; VAS, Visual Analog Scale.

The study flowchart is shown in figure 1.

Sample size

The sample size was determined by using GPower (V.3.1; Informer Technologies) with the VAS Score at rest as the primary outcome parameter. The usual acceptable postoperative difference in VAS pain score is approximately 1–2 points, according to previous studies; therefore, a difference of 2 points was chosen as the minimum clinically important difference.19 The minimum effect size (δ) was greater than 1 point with a power of 0.9 and an α<0.05 with the inclusion of at least 23 patients in each group.

Participants

At the time of the preoperative assessment, patients who are scheduled for elective knee surgery under spinal anaesthesia will be screened and recruited. Written informed consent will be obtained from patients who meet the inclusion criteria. The consent forms will be provided in the local language. Trial participants will be allowed to withdraw at any time.

Inclusion criteria

Unilateral primary knee surgery.

Age between 50 and 85 years.

Exclusion criteria

Body mass index (BMI)>40 kg/m2.

Allergy or intolerance to opioid analgesics.

A history of deep vein thrombosis or pulmonary embolism.

American Society of Anesthesiologists (ASA) Classification III or higher.

Progressive neurological deficits.

Coagulopathy.

Randomisation and allocation concealment

Participants will be randomly assigned in a 1:1 ratio to either the FNB group or the PMP group. Assignment will be carried out in numerical order using sealed, opaque envelopes and a computer-generated random sequence.

Blinding

The orthopaedic surgeons will be blinded while the attending anaesthesiologist performs the nerve block. The nerve block will be performed by the attending anaesthesiologist, who will not involve in data collection and analysts. An independent researcher will be involved in postoperative follow-up and data collection. The orthopaedic surgeons, data collectors and analysts will have no knowledge of patient treatments or groupings.

Patient and public involvement

Neither the patients nor the public were involved in the design, recruitment or execution of the study.

Study procedure

At admission, demographic information including age, sex, BMI and ASA functional status will be recorded. Preoperatively, patients will fast for 8 hours and drink 100 mL of clear carbohydrate liquid 2 hours before surgery. ECGs, pulse oximetry and non-invasive blood pressure will be continuously monitored prior to the surgical procedure.

Patients without contraindications to intralesional anaesthesia will undergo spinal anaesthesia. Spinal anaesthesia will be induced with 3 mL of 0.5% ropivacaine at the L3/4 interspace. Additionally, postoperative intravenous antiemetic prophylaxis comprising dexamethasone (5 mg) and tropisetron (5 mg) will be administered. Intraoperative haemodynamic stability will be consistently maintained. For routine postoperative pain management, patient-controlled analgesia (PCA) consisting of sufentanil (100 µg) and tropisetron (10 mg) dissolved in 100 mL of saline will be used. The PCA settings will include a loading volume of 2 mL, a background dose of 2 mL/hour, a lock time of 15 min and a maximum dose of 10 mL/hour. Before the disappearance of postoperative spinal anaesthesia, peripheral nerve blocks will be performed. Patients will be assigned to receive either an FNB or a PMP block, with a direct-shot administration of 30 mL (0.5% ropivacaine + 5 mg dexamethasone) used for both groups.

InterventionsFNB group

Patients will be placed in the supine position, the inguinal area will be sterilised before the operation, and the ultrasound probe will be placed along the transverse axis near the groin. The depth of ultrasound scanning and the position of the probe will be adjusted as needed, and the femoral artery will be the localising structure in the FNB operation. Sufficiently clear ultrasound images will be obtained, local anaesthesia will be induced, a puncture needle will be placed posterior to the femoral nerve, and 30 mL of the study drug will be injected with ultrasound guidance.

PMP block group

Similarly, patients will be placed in the supine position with preoperative sterilisation of the inguinal region. The ultrasound probe will be positioned along the transverse axis near the inguinal region with adjustments made to depth and probe positioning to identify the pectineus muscle at the inferior medial invagination of the inguinal region. Clear ultrasound images will be obtained. A needle will be inserted into the patient’s medial thigh, local anaesthesia will be induced, and the needle will be advanced to the fascial plane below the pectineus muscle. Under ultrasound guidance, 30 mL of the study drug will be injected.

OutcomesPrimary outcomes

The primary outcomes will be the VAS pain score at rest and during movement at 2, 4, 8, 12, 24 and 48 hours after surgery. VAS scores range from 0 to 10, with 0 indicating no pain and 10 representing the worst pain.

Secondary outcomes

The secondary outcomes will include the results from the straight-leg-raise test, out-of-bed test and the 20 m walk test at 24, 48 and 72 hours after surgery; degrees of active flexion; total dose received from PCA infusion pumps; number of compressions; length of hospital stay; patient satisfaction20–22; and postoperative complications such as pulmonary embolism and deep vein thrombosis. We will measure patient satisfaction scores using the VAS (0=completely dissatisfied and 10=completely satisfied). Patient satisfaction is easily measured. The local language will be used while administering these assessments. The straight-leg-raise test will be used to determine if and when the patient is capable of moving without using their hands. The patients will be asked to leave their bed and stand with the help of a walker; then, the ability to walk 20 m with the walker will be recorded. The results of each assessment are shown in figure 2.

Figure 2

Standard protocol items.

Safety evaluation

The specific time, severity, duration and connection between peripheral nerve block and any adverse events will be noted during the trial. The following five grading criteria will be used to assess the relationship between adverse events and peripheral nerve block: (1) some association, (2) potential correlation, (3) total unrelatedness, (4) potential unrelatedness and (5) ambiguity regarding the countermeasures performed and the outcome.23

Quality control of inpatients

Prior to testing, uniform training will be provided to all anaesthesiologists, assessors and statisticians in nerve block manipulation, inclusion and exclusion criteria, standardised methods, observation time, outcome data collection and technical data processing. Patients and their families will be trained in the use of the intravenous PCA pumps and nerve block therapy techniques. To ensure the quality of this trial, clinical supervisors will frequently check on the study.

Data collection and management

We will compile the primary and secondary outcomes as shown in the tables. The corresponding author will provide the data for this study on reasonable request. Due to privacy and ethical concerns, these data will not be made public. The original information, which includes the case report form and related documents, will be kept for ten years before being destroyed in compliance with hospital policies.

Statistical analysis

Student’s t-test will be used to compare all continuous data, which will be reported as the mean and standard deviation (upper and lower 95% CI). Fisher’s exact test or Pearson’s χ2 test will be used to evaluate discontinuous data, which will be reported as frequencies (percentages). A p value<0.05 will indicate significant differences at all raw significance levels. All the statistical analyses will be performed using SPSS V.20.0.

Discussion

The effective management of pain following knee surgery is pivotal for improving patient prognosis. While FNB has been demonstrated to reduce pain, it is associated with quadriceps muscle weakness, potentially impacting patient outcomes.24 Thus, the aim of this study is to explore the efficacy of PMP block in augmenting postoperative analgesia and facilitating early functional exercise. The primary objectives are to assess the efficacy and safety of PMP block.

Compared with FNB, PMP block may offer several advantages. First, a cadaver study confirmed that PMP blockade can block the anterior and posterior obturator and saphenous nerves. This approach may provide more effective postoperative analgesia. Second, earlier functional exercise promotes early recovery and shortens the hospital stay. Third, there may be potential benefits for geriatric patients who cannot remain bedridden for long periods due to the presence of pulmonary disease. Previous research has implicated postoperative pain in direct nerve damage or inflammation resulting from tissue trauma.25 Pain perception is facilitated through nociceptive afferent pathways targeted by various drugs. Anaesthetic drugs and non-steroidal anti-inflammatory drugs can inhibit nociceptor activity, thereby mitigating pain.25 Peripheral nerve blocks, including sciatic nerve, obturator nerve and FNBs, have been widely employed for postoperative analgesia in knee surgery patients.26 27 Although the use of 30 mL of study medication for FNB might be considered controversial, Grevstad et al 24 have demonstrated its safety and rationale in clinical trials. Similar to FNB, PMP block can cause adverse effects, such as nerve damage, infection and systemic toxicity of local anaesthetics. Nonetheless, this study introduces an innovative approach to postoperative pain management for knee surgery patients.

Despite the potential benefits, our trial has some limitations. First, the sample size is small. Second, as a long-acting glucocorticoid, dexamethasone may elevate blood sugar levels, which are not being monitored before, during or after surgery. Third, while perioperative administration of intravenous or peripheral dexamethasone may reduce the incidence of postoperative nausea and vomiting following knee surgery,28 29 existing research shows no statistically significant difference in these outcomes between individuals receiving dexamethasone and those receiving ropivacaine alone.

Fourth, this trial will not measure quadriceps muscle strength to evaluate motor nerve block. Evidence suggests that compared with patients who receive PCA, patients who receive peripheral nerve blocks recover faster. We chose this procedure to compare the effectiveness of FNB and PMP block for pain management in knee surgery patients.

Ethics and dissemination

Before taking part in this study, all participants who meet the diagnostic, inclusion and exclusion criteria must complete an informed consent form. The study was approved by the ethics committee of Zhejiang Hospital (2022(128K)). The results of this study will be published in peer-reviewed journals.

Ethics statementsPatient consent for publication

Not applicable.

Acknowledgments

We want to thank all the contributors and collaborators for their support in this study. We also thank all the participating patients.