Currently, the analgesic standard of care for patients undergoing total hip arthroplasty (THA) at our centre is intraoperative infiltration with a solution of local anesthetic, morphine (opioid), and ketorolac (nonsteroidal anti-inflammatory drug - NSAID). If a patient has a contraindication for the use of an opioid or NSAIDs, this infiltration is performed with a plain local anesthetic. No blocks (numbing of certain nerves to prevent pain from occurring in that area) are performed for postoperative pain in these patients. The pericapsular nerve group (PENG) block is a recently described technique with limited data in the literature that has assessed the benefits of using this nerve block for THA procedures. The purpose of this study is to investigate if the ultrasound-guided PENG block can provide non-inferior postoperative analgesia compared to local intraoperative anesthetic infiltration (ILAI) with an associated cost benefit for patients undergoing THA.

Traditionally, the most common ultrasound-guided nerve blocks utilized for hip analgesia during THA are the Femoral Nerve Block and the Fascia Iliaca Block. Despite the analgesia component of both techniques, they can cause quadriceps weakness1-2, which is an unwanted side effect for this patient population as it interferes with surgical recovery, physical therapy, and increases the risk of fall. For these reasons, these types of blocks are not performed for patients undergoing THA at our center (London Health Science Centre).

In 2018, a cadaveric study performed by Short et al. demonstrated that the hip capsule is innervated by sensory branches of the Femoral Nerve and Accessory Obturator Nerves.3 An ultrasound-guided technique for the blockade of the articular branches of the hip was first described by Giron-Arango et al.4 The major benefit of using this approach is the possible motor-sparing effect, capable of maintaining the quadriceps muscle force as the technique aims only at sensory articular branches.

The current standard care for postoperative analgesia for THA is intraoperative infiltration with a solution containing ropivacaine 0.25% (local anesthetic), morphine (opioid), and ketorolac (NSAID). Patients with any contra-indication for the administration of opioids, or nonsteroidal anti-inflammatories receive intraoperative infiltration with plain local anesthetic.

The efficacy of ILAI for THA remains inconclusive. While some studies validated the benefit of this technique5-9, others were not able to confirm improvements in pain control.10-15 As it is a simple technique based on the injection of analgesic solution in the tissue surrounding the surgical field, it has become a popular intervention.

Similarly, the analgesic efficacy of the PENG block for THA remains unclear. As the PENG block involves sensory articular nerves of the anterior hip capsule, the benefit for the patients lies in the possibility of having a good analgesic response along with no motor leg weakness. This will improve patient care during the postoperative period with early mobilization and adequate pain control. There is limited information in the literature available regarding the use of the PENG block as part of the postoperative analgesia plan for THA. Thus, we have identified a need to conduct a trial that aims to investigate if the ultrasound-guided PENG block can provide non-inferior postoperative analgesia compared to local intraoperative anesthetic infiltration (ILAI).

In 2020, a retrospective case series by Kukreja et al16 evaluated twelve patients that underwent total hip arthroplasty (six primaries, six revisions). This study showed a decrease in opioid consumption in the primary THA group. In this group, two patients had spinal anesthesia as the primary anesthesia technique, while four received general anesthetic. Hence, the results of this study have suggested that the PENG block may be useful for postoperative analgesia in this procedure.

Following this case report series, Aliste et al17 conducted a randomized trial comparing the ultrasound-guided PENG block with the ultrasound-guided suprainguinal fascia iliaca block with the purpose of evaluating the postoperative incidence of quadriceps motor block as the primary outcome. In this study, the PENG block resulted in a lower incidence of quadriceps motor block compared with the suprainguinal fascia iliaca block.

In addition, two randomized clinical trials were conducted in 2022 involving the addition of the ultrasound-guided PENG block in the analgesic plan for patients that underwent THA demonstrating benefits. Both of these studies demonstrated benefits of incorporating the PENG block into the analgesic care plan for this patient population. First, Lin et al18 conducted a randomized clinical trial in which patients received either a PENG block or a sham block in addition to spinal anesthesia and ILAI (100ml of ropivacaine 0.1% with 1mg of epinephrine). In this study, the patients that received the PENG block had less postoperative pain with preservation of quadriceps muscle strength.

Second, Zheng et al19 performed a similar randomized trial in which patients undergoing THA were randomized to the intervention group that received the PENG block, or to the placebo group in which a PENG block was simulated with an injection of 20ml of normal saline solution. All patients had general anesthesia as the main anesthetic plan and received an ILAI with 20ml of ropivacaine 0.5% by the end of the procedure. The study showed that the addition of a PENG block provided a limited advantage to postoperative analgesia in the Post-Anesthesia Care Unit (PACU) and lower intraoperative opioid consumption.

At this point, in our understanding, no further clinical data is available comparing the analgesic efficacy of PENG block with ILAI. Further clinical trials are needed to test the efficacy of PENG blocks.

Following consent, patients will be randomized to one of two study groups (on a 1:1 basis):

Group 1: patients will receive ultrasound-guided PENG block (PENG group) with local anesthetics (20 ml of 0.5% ropivacaine) before administration of spinal anesthesia. Patients in this group will also receive a sham ILAI procedure with 60 mL of saline (performed by the operating surgeon).

Group 2: patients will receive a sham PENG block performed with 20ml of normal saline solution before spinal anesthesia. After, patients will receive ILAI (performed by the operating surgeon) with a plain solution of ropivacaine 0.25% 60ml.

The block group (PENG group), will be administered a single dose of ultrasound-guided PENG block with 20ml of ropivacaine 0.5% drawn up by an anesthesiologist in the BR before the spinal anesthesia. All patients will be offered Midazolam 1-2 mg IV before the start of the interventions. In the control group, a sham PENG block with 20ml of normal saline will be performed before spinal anesthesia. After, ILAI will be performed by the operating surgeon with a plain solution of ropivacaine 0.25% 60ml. In both groups, the anesthesiologist will be blinded to perform the PENG and Sham block. Next, spinal anesthesia will be performed with bupivacaine 0.5% 15mg intrathecally. The spinal anesthesia will be tested for sensory block to cold using an alcoholic chlorhexidine pad, and for motor block by asking the patient to move either leg. The timing of the completion of the spinal anesthesia will be marked and it will be considered time zero. Next, the patient will be moved to the main OR for surgery. Intraoperative sedation will be at the discretion of the OR anesthesiologist. If spinal anesthesia fails, the patient will receive general anesthetic in the operating room. This patient will however remain in the study group as "intention to treat".

A blinded data collector will record all outcomes (NRS pain score, PACU length, muscle strength, and intraoperative opioid consumption). The timing of the completion of the spinal anesthesia will be considered time zero. At 8 hours and 24 hours after the end of the spinal anesthesia, the patient will be approached by the blinded data assessor to collect the NRS pain score. Pain score evaluation will be recorded at rest, on passive movement, and on active movement of the operated hip joint. Also, the quadriceps muscle strength will be evaluated by the capacity of the patient to perform knee extension at 8 hours and 24 hours postoperatively. Data will be collected for the patient's opioid consumption in the 24 hours after the spinal anesthesia was completed. Pain assessment and muscle strength will be evaluated using the following scales:

Pain assessment: A Likert-like numerical rating scale (NRS) will be used for pain assessment, 0 = no pain, 1-3= mild pain, 4-6= moderate pain interfering with activity, and 7-10= severe, disabling pain.

Muscle strength: The quadriceps muscle function will be evaluated. Strength testing of the quadriceps will include the resistance of knee extension and hip flexion. Commonly used muscle testing grading will be used:

Grade 5: Full range of motion against gravity with maximal resistance Grade 4: Full range of motion against gravity, moderate resistance Grade 3: Full range of motion against gravity Grade 2: Full range of motion, gravity eliminated Grade 1: Visible or palpable contraction without motion Grade 0: No visible or palpable contraction

All patients will be offered oral opioids on an as-needed basis. The total amount of opioids administered to the patient in the 24 hours after the neuraxial procedure will be evaluated.

Inclusion Criteria:

1. Adult patient (>18 years old)
2. Undergoing THA with a direct lateral surgical approach (transgluteal approach)
3. Ability to provide verbal/written consent to participate in this trial

Exclusion Criteria:

1. Patient with any contraindication for spinal anesthesia
2. Patient with any contraindication for regional analgesia
3. Patient undergoing THA with a direct anterior surgical approach
4. Patients undergoing THA for hip revision
5. Patients undergoing THA under One Day Stay (ODS) admission
6. Patients that received opioids intrathecally
7. Patients having residual motor block six hours after the completion of the spinal anesthesia.
8. Patients with a history of regular opioid intake for more than three months
9. Patients incapable of performing knee extension of the same operative side
10. Pregnant patients