This trial aims to assess the analgesic effect of Popliteal Plexus Block (PPB) with 10 mL versus 20 mL of Bupivacain 5 mg/mL, when applied as an adjunct treatment to a multimodal analgesic regimen following primary total knee arthroplasty. We hypothesize that PPB with 20 mL of local anesthetic reduces 24-hour postoperative opioid consumption (= primary outcome) compared to 10 mL after TKA.

Secondary outcome include

• the frequency of 24-hour opioid-free analgesia
• pain intensity at rest and during mobilization
• Manual Muscle Tests and ability to mobilize with crutches six hours after end-of-surgery
• and patients reported outcomes using the Quality of Recovery 15 survey 24 hours after end-of-surgery.

Participant will:

• undergo primary total knee arthroplasty in spinal anesthesia.
• recieve a PPB with either 10 mL of Bupivacaine or 20 mL.
• recieve a multimodal analgesic regime including a Femoral Triangle Block.
• Have 10 scored morphine tablets available for self-administration within the first 24 postoperative hours after end-of-surgery.
• be examined by a physiotherapist 6 hours (±1 hour) after end-of-surgery to assess pain scores, manual muscle testing of ankle and knee function, and the ability to mobilize with crutches.
• complete a survey 24 hours after end-of-surgery to assess self-administered morphine intake, pain scores, and Quality of Recovery-15.

Patients will undergo primary unilateral total knee arthroplasty with insertion of non-cruciate retaining standard cemented prosthesis by a parapatellar medial approach, without use of tourniquet or Local Infiltration Analgesia.

For the spinal anesthesia, 3 mL of Ropivacaine 5 mg/ml will be applied.

All patients will receive a femoral triangle block in combination with the PPB, both administered immediately after surgery in the post-anesthesia care unit.

Description of the PPB procedure:

The superficial femoral artery is identified at mid-thigh level and traced caudally until it deviates from sartorius muscle and is positioned adjacent to the posteromedial margin of the vastus medialis muscle, close to the adductor hiatus. The needle will be inserted medially to the transducer and advanced in-plane through the sartorius muscle targeting the endpoint of injection in the distal part of the adductor canal, on the top of the superficial femoral artery, posteromedial to the fascia of the vastus medialis muscle. We will inject the allocated volume of bupivacaine 5 mg/mL, ensuring anterolaterally spread to the artery

The Femoral Triangle Block uses 15 mL of Bupivacaine 5 mg/mL (10 mL applied in the femoral triangle to target the saphenous nerve and nerve to vastus medialis and 5 mL applied to target the intermediate femoral cutaneous nerve located at the superficial side of the sartorius muscle).

The multimodal analgesic regime also consists of a Dexamethasone 12 mg IV (administered perioperatively), Paracetamol (1000 mg) x 4 daily + NSAID (400 mg) x 3 times daily postoperatively, inclusing preoperatively administration of Paracetamol 1000 mg and Ibuprofen 400 mg.

The scored morphine tablets allows the patients to take 5 mg morphine at a time, with a maximum oral dose of 100 mg within the first 24 hours after end-of-surgery time. If needed, hospital staff can administer rescue doses of intravenous morphine, which will be recorded in the patient file. Total opioid consumption will be reported as oral morphine milligram equivalents (MME), combining hospital-administered opioid doses from the patient file and self-reported intake of dispensed morphine tablets.

Inclusion Criteria:

• Scheduled to undergo primary total knee arthroplasty in spinal anesthesia.
• Ability to give their written informed consent after having fully understood the contents of the study.
• American Society of Anesthesiologists (ASA) physical status 1, 2, or 3.

Exclusion Criteria:

• Patients who cannot read or speak Danish.
• Patients who cannot operate or have access to a smartphone with internet connectivity (required for patient-reported outcome assessment).
• Patients with allergies or intolerance to the medicines used in the study.
• Patients with a consistent daily intake of opioids preoperatively.
• Patients who are dependent on walking aid devices preoperatively.
• Patients suffering from alcohol and/or drug abuse - based on the investigator's assessment.
• BMI > 40.
• Diagnosed with chronic neurodegenerative disorders.

Data is available upon reasonable request.

Good-Clinical-Practice monitor is also blinded.