Total knee arthroplasty (TKA) is among the most frequently performed surgical procedures for degenerative joint diseases, including advanced knee osteoarthritis, rheumatoid arthritis, and post-traumatic arthritis. More than 700,000 TKA procedures are performed annually in the United States alone since 2012, with projections estimating a 143% increase by 2050. A significant proportion of patients experience moderate to severe postoperative pain following the procedure, adversely affecting early mobilization, adherence to rehabilitation programs, and ultimately functional recovery .

Femoral nerve block (FNB) was historically the cornerstone of TKA analgesia; however, concerns about quadriceps weakness and associated fall risk led to its replacement by more motor-sparing alternatives . Adductor canal block (ACB) has since become the standard approach, providing analgesia equivalent to FNB while significantly preserving quadriceps strength . Nevertheless, ACB does not adequately cover the posterior capsule and popliteal plexus terminals; consequently, 60-80% of TKA patients report significant posterior knee pain that cannot be sufficiently managed by ACB alone .

To address this limitation, several posterior knee analgesia techniques have been described. The IPACK (Interspace between Popliteal Artery and Capsule of the Knee) block targets genicular nerve branches and popliteal plexus terminals by injecting local anesthetic between the popliteal artery and the posterior knee capsule, largely sparing the main motor trunks and providing selective posterior analgesia . The adductor magnus muscle plane (AMM) block is a relatively novel interfascial plane block technique applicable in the supine position simultaneously with ACB. By injecting local anesthetic into the fascial plane along the posterior surface of the adductor magnus muscle, the AMM block aims to spread to the popliteal plexus and posterior capsular branches, potentially mimicking a sciatic nerve block effect . A key advantage of the AMM block is its applicability without patient repositioning during the same session as ACB.

The primary objective of this prospective randomized trial was to compare the effects of IPACK and AMM blocks-both added to ACB-on postoperative opioid consumption in patients undergoing TKA. Secondary objectives included evaluating the impact of each technique on postoperative pain scores, mobilization time, functional recovery, and motor function

Study Design and Ethical Approval This prospective, randomized, parallel-group trial was approved by the Ethics Committee of Atatürk University Faculty of Medicine (Decision No. 5, Meeting No. 7, dated October 26, 2023). Written informed consent was obtained from all participants before enrollment.

Patients aged 18-75 years with American Society of Anesthesiologists (ASA) physical status I-III scheduled for primary total knee arthroplasty (TKA) were eligible. Exclusion criteria included hepatic, renal, or advanced cardiac insufficiency; neuropathic pain; use of analgesics within 24 hours before surgery; coagulopathy or anticoagulant therapy; advanced cardiovascular disease; allergy to study medications; inability to cooperate; chronic opioid use; and previous lumbar instrumentation.

Of 90 patients assessed for eligibility, 30 were excluded because of chronic renal failure (n = 3), chronic opioid use (n = 5), anticoagulant therapy (n = 8), inability to cooperate (n = 10), or L2-L4 vertebral instrumentation (n = 4). Sixty patients were included and randomized equally into two groups: IPACK (n = 30) and AMM (n = 30).

Randomization and Blinding Participants were randomized in a 1:1 ratio using a computer-generated randomization sequence one hour before surgery. Allocation assignments were concealed in sealed opaque envelopes and delivered to the operating room technician responsible for preparing the intervention.

The anesthesiologist performing the regional block could not be blinded because of the procedural differences. However, patients, surgeons, and the investigator responsible for postoperative outcome assessment were blinded to group allocation.

Regional Anesthesia Procedures ACB Block All patients received an ultrasound-guided adductor canal block (ACB) combined with either an infiltration between the popliteal artery and capsule of the knee (IPACK) block or an adductor magnus muscle plane (AMM) block.

For the ACB, patients were positioned supine with slight external rotation of the hip. After ultrasound identification of the adductor canal, correct needle placement was confirmed with 2 mL of 0.9% saline, followed by injection of 10 mL of 0.5% bupivacaine diluted with 10 mL of 0.9% saline. Dermatomal sensory assessment was performed 5 minutes after injection.

IPACK Block With the patient supine and the knee slightly externally rotated, the ultrasound transducer was placed transversely on the medial aspect of the distal thigh. After identifying the distal femur and popliteal artery, the needle was advanced in-plane into the interspace between the popliteal artery and femur. Following negative aspiration and saline confirmation, 10 mL of 0.5% bupivacaine and 10 mL of saline were injected with intermittent aspiration every 5 mL.

AMM Block The transducer was positioned medially over the distal thigh to identify the adductor muscle compartment. The needle was advanced in-plane from anteromedial to posterolateral until a fascial "pop" indicated entry into the posterior compartment. After negative aspiration and saline confirmation, 10 mL of 0.5% bupivacaine and 10 mL of saline were administered. In the AMM group, the subsequent ACB was performed through needle redirection without a second skin puncture.

For all procedures, needle tip visibility, needle shaft visibility, number of needle insertions, and block performance time were recorded. Dermatomal coverage of the tibial, common peroneal, sural, saphenous, and posterior femoral cutaneous nerves was assessed at 5, 10, 15, 20, 30, and 45 minutes after block placement.

Anesthetic Management Standard monitoring, including electrocardiography, pulse oximetry, and noninvasive blood pressure monitoring, was applied in the operating room. Before spinal anesthesia, patients received intravenous midazolam 2 mg, ondansetron 8 mg, and dexamethasone 8 mg.

Spinal anesthesia was performed under sterile conditions at the L3-L4 or L4-L5 interspace using a 25-gauge spinal needle. Following confirmation of cerebrospinal fluid flow, 15 mg hyperbaric bupivacaine was administered intrathecally. Surgery commenced after a sensory block level of T10 was achieved.

Surgical Technique All TKAs were performed under spinal anesthesia using a standard medial parapatellar approach. After exposure of the knee joint, the anterior cruciate ligament and osteophytes were removed, and femoral and tibial bone cuts were performed using standard alignment guides. Trial components were inserted to assess fit, alignment, stability, and range of motion. Final femoral, tibial, and polyethylene components were implanted using a cemented technique with one package of bone cement.

A negative-pressure intra-articular drain was placed before layered wound closure. The procedure concluded with application of a Jones compression bandage.

Perioperative Analgesia Paracetamol 1 g was administered intravenously 30 minutes before completion of surgery and continued every 8 hours postoperatively. Dexketoprofen trometamol 25 mg was administered intraoperatively 30 minutes before the end of surgery and continued every 12 hours postoperatively.

Postoperative analgesia was provided using intravenous patient-controlled analgesia (PCA) with fentanyl (10 µg/mL concentration, 25 µg bolus dose, 15-minute lockout interval, 48-hour duration). In addition, all patients received paracetamol 1 g three times daily and dexketoprofen 25 mg twice daily as part of a multimodal analgesic regimen.

Patients with a visual analog scale (VAS) score ≥ 4 in the recovery room received rescue tramadol 100 mg intravenously. Patients achieving an Aldrete score ≥ 9 were transferred to the ward.

Outcome Measures The primary outcome was postoperative opioid consumption. Secondary outcomes included postoperative pain scores, motor function, mobilization, and functional recovery.

VAS pain scores and adverse events were recorded at 1, 2, 4, 8, 12, 24, and 48 hours postoperatively. Opioid consumption was assessed during the 0-4, 4-8, and 8-24 hour intervals and as a cumulative 24-hour total.

Motor block of the quadriceps femoris and tibialis anterior muscles was evaluated using a three-point scale (0 = paralysis, 1 = paresis, 2 = normal strength) immediately after surgery and at 12, 24, and 48 hours.

Preoperative assessments included walking aid use, presence of varus-valgus deformity, anterior and posterior VAS scores, Timed Up and Go (TUG) test, quadriceps muscle strength, and active range of motion (ROM). The TUG test measured the time required to stand from a chair, walk 3 meters, return, and sit down. Quadriceps strength was assessed isometrically, and active ROM was measured using a goniometer.

On postoperative days 1 and 2, mobilization time, VAS scores, TUG performance, quadriceps strength, ROM, and the Five Times Sit-to-Stand Test (FTSST) were recorded.

Inclusion Criteria:

• Anesthesiologists (ASA) physical status I-II-III
• Total Knee Arthroplasty Surgery

Exclusion Criteria:

• cardiovascular disease,
• hepatic dysfunction,
• coagulopathy or current use of anticoagulant therapy,
• inability to cooperate,
• known allergy to any of the study medications,
• refusal to participate in the study