The purpose of this study is to assess the effectivity of adductor canal block performed the day after total knee arthroplasty surgery in reducing pain and improving walking ambulation ability and muscle strength.

Overview: total knee arthroplasty is a painful procedure. According to our institutional pain registers the worst pain appears in postoperative day one, which could be related to the use of effective but short analgesic intraoperative techniques like periarticular local analgesic infiltration and intravenous multimodal analgesia.

The aim: to asses if adductor canal block performed the day after primary total knee arthroplasty (16-20 hours postoperative) improves analgesia without motor blockade and impairment of early ambulation ability.

Primary Hypothesis: adductor canal block performed 16-20 hours after primary total knee arthroplasty improves postoperative analgesia.

Secondary Hypothesis: adductor canal block performed 16-20 hours after primary total knee arthroplasty improves ability of early ambulation, adductor and quadriceps strength after primary total knee arthroplasty.

The objectives:

1. To compare postoperative pain control effects between adductor canal block and placebo block.
2. To assess the improvement of ability of early ambulation and extent of motor blockade after primary total knee joint replacement surgery between the groups of patients.
3. To estimate variations in quadriceps and adductor muscle strength in the two groups of patients.
4. To asses related side effects to adductor canal nerve block.
5. To asses variations in length of stay between the two groups.

Methods:

The prospective, double-blinded study includes American Society of Anesthesiologists (ASA) physical status I-III in preoperative assessment, aged 18-85 years, admitted for primary total knee arthroplasty. Preoperatively a simple randomization is made to distribute the included patients in two groups: Standard Group and Intervention Group. A table of random numbers is used, first selecting the starting point and later the movement direction remains constant throughout the whole table. The even numbers are allocated in the Standard Group and the odd ones in the Intervention group. The anesthesiologist performing the block will be aware of the treatment, but the participant subject and outcomes assessor will be blinded to the group assignment.

During the perioperative period all patients from both groups will receive a standardized anesthetic and analgesic treatment: premedication with midazolam 2.5-5 mg and dexamethasone 0'1 mg/kg, spinal anesthesia with 10mg of hyperbaric bupivacaine and intravenous propofol during the surgery for sedation. As analgesia paracetamol 1gr plus dexketoprofen 50 mg. The local infiltration analgesia will be performed in a protocolized manner during the surgery with ropivacaine 0'2% 120 cc mixed with 0'6 mg adrenaline and at the end of surgery with ropivacaine 0'2% 40cc for subcutaneous infiltration. Two doses of 0'1mg/kg tranexamic acid are administrated unless contraindication, first one 30 min before skin incision and second one three hours later.

Postoperative analgesia will be administrated to both groups of patients with ibuprofen 600 mg/8h and paracetamol 1gr/6h. Opioids will be available to patients as intravenous boluses of tramadol 1mg/kg if pain numerical rate score (NRS) > 3 at rest or > 5 at movement.

All patients included in the study are transferred to post-anesthesia reanimation unit 16-20h after surgery, in postoperative day one. The operated extremity is slightly externally rotated and prepared for the block with 2% chlorhexidine and sterile dressing and the adductor canal is identified with ultrasound image at the mid-thigh level. In standard group patients a sham adductor canal block with 2ml of 1% subcutaneous lidocaine is done. In intervention group patients an adductor canal block with a 22 Gauge ultrasound-visible needle and 20 ml of 0'5% ropivacaine is done. At the end all patients have a sterile apposite on the puncture site.

Postoperative pain will be assessed 15 minutes before the procedure (adductor or sham block), 2 hour, 24 hour post and also in the three nursing rounds (morning, afternoon, night) the first 72 hours after surgery. The pain numeric rating scale (NRS) is used (from 0 - no pain to 10 - worst imaginable pain) at rest and during active knee flexion. The requirement of additional opioids and their side effects (if any) will be recorded.

Knee extensor and adductor muscle strength is measured using a hand-held dynamometer (Baseline Digital Hydraulic Push Pull Dynamometer R)) immediately prior to surgery, in first postoperative, day immediately before the procedure, 2 hours and 24 hour postprocedure.

Patients ability of early ambulation is evaluated using ten meter walk test (TMWT) in the first and second postoperative day every 12h.

The success rate of the block is assessed by testing for sensation of cold and pinprick stimulus at the medial midcalf using a 3-point scale (2 = normal sensation, 1 = decreased sensation, 0 = no sensation) 2 hours after block.

The length of hospital stay and rate of complications (if any), will be recorded in both groups of patients. Complications will be graded as local complications (hematoma, wound complications…), block complications (falls, vascular injection…), urinary complications (acute urine retention, renal failure…) and general complications (neurological, respiratory, cardiological…).

According to study protocol, both groups of patients will be compared in terms of postoperative pain control, opioid consumption, postoperative nausea and vomiting, quadriceps strength, adductor strength, ability of early ambulation, length of hospitalization and complications.

Inclusion Criteria:

• Patients undergoing elective unilateral total knee arthroplasty
• American Society of Anesthesiologist (ASA) class 1-3
• Adults aged 18-85 years old

Exclusion Criteria:

• Contraindications of the adductor canal block.
• Contraindications of the local infiltration analgesia technique.
• Chronic kidney disease
• Surgery to be performed under general anesthesia.
• Opioid treatment > 30 mgr morphine or equivalent for more than 3 months time.
• Neuropathic ipsilateral pain.
• Inability to understand study procedures.
• Not acceptance of the procedure (adductor canal block or local infiltration analgesia).

All patients included in the study are transferred the day after the total knee arthroplasty surgery to the postoperative resuscitation unit.

A sterile dressing of the lower extremity is performed and after the adductor canal is identified with ultrasound image, a medial leg puncture is done with or without doing the canal adductor block. At the end all patients have a sterile apposite on the puncture site.

All variables and outcomes are collected and registered by people not involved in the realization of the intervention.