Magnesium Sulfate in Adductor Canal Blocks

Study Overview
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Brief Summary
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Proper analgesia after total knee arthroplasty (TKA) is important for encouraging early ambulation, which can facilitate improved patient outcomes and early hospital discharge. For pain control after TKA, adductor canal blocks (ACBs) improve upon the gold standard femoral nerve blocks (FNBs) since they do not cause as much quadriceps muscle weakening, while providing equivalent analgesia. Multimodal analgesia has become commonplace as a method of superior pain control with fewer side effects. Magnesium sulfate as an adjuvant to FNB local anesthetics can improve pain control after surgery; however, it also prolongs time to ambulation. There are no reports on the effect of magnesium sulfate in ACBs on analgesia after TKA. Thus the purpose of this randomized, double-blind, controlled trial is to determine whether magnesium sulfate given with local anesthetics via ACB can prolong analgesia, reduce pain scores and opioid consumption, and increase mobilization in TKA patients.

Detailed Description
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Adequate analgesia after surgery is important for patient well-being, satisfaction, rapid recovery, and timely discharge. Due to our aging population, total knee arthroplasties (TKAs) are an increasingly common surgical procedure in Canada, with 57,718 performed in 2012-2013 alone. Improved functional outcomes and early hospital discharge are facilitated when patients ambulate within several hours of surgery. Early ambulation is enabled by good analgesia without concomitant muscle weakness or debilitating side effects associated with opioid consumption. Given the high volume of knee replacements, the need to ambulate early, and the importance of effective pain management, the development of new analgesia techniques for TKAs is an important endeavor to reduce hospital costs and improve the quality of life of a substantial number of patients. In order to minimize adverse side effects while still providing adequate postoperative analgesia, many anesthesiologists now co-administer smaller doses of several different medications, which act additively or synergistically depending on their combined and varied mechanisms of action. Often these medications are given locally, either directly into the knee (periarticularly) or near the nerves innervating the knee, for example the femoral nerve block (FNB) or the adductor canal block (ACB). FNBs, wherein local anesthetic medications are injected around the femoral nerve, are commonly used to manage pain following TKA. Although they assist in providing quality postoperative pain relief, FNBs are also associated with weakening of the quadriceps muscle, and an increased risk of falls. The ACB involves an injection of local anesthetics such as ropivacaine or bupivacaine into the adductor canal in the middle third of the thigh, which contains the sensory saphenous nerve. ACB is as effective as FNB at reducing postoperative pain in TKA patients. However, ACBs do not cause quadriceps weakening to the same extent as FNBs, and result in earlier recovery of ambulation after surgery compared to FNBs. Since ACBs produce less quadriceps weakening (due to their actions on sensory, rather than motor, nerves), this anesthetic technique may reduce the risk of falling in the postoperative period compared to FNBs; however, most studies are underpowered to detect this statistically. Recent attention has been given to magnesium sulfate (MgSO4) as a supplement to improve and/or prolong local anesthesia postoperatively. MgSO4 is thought to reduce pain via antagonism of N-methyl-D-aspartate (NMDA) receptors. A local mechanism of action on peripheral rather than central NMDA receptors is supported by studies showing that despite providing pain relief, peripherally administered MgSO4 does not increase cerebrospinal fluid concentrations of magnesium, implying that it cannot cross the blood-brain barrier to enter the central nervous system. In knee surgery patients, locally administered MgSO4 via the periarticular route reduces postoperative pain, reduces cumulative analgesic consumption, and prolongs analgesia. MgSO4 co-administered with local anesthetic via FNB in knee surgery patients reduces pain and postoperative analgesic consumption compared to local anesthetic alone; however, it also prolongs the time to ambulation, which could delay hospital discharge. Currently, there are no investigations into the analgesic efficacy of MgSO4 administered via ACB in TKA patients. Therefore, the purpose of this randomized controlled trial is to assess the duration of analgesia in TKA patients receiving ACBs with or without MgSO4. The investigators hypothesize that patients receiving MgSO4 will have prolonged analgesia, improved pain scores, and will be able to mobilize further, all of which will contribute to a shorter hospital length of stay in these patients.

Official Title
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Does Magnesium Sulfate as a Supplement in Adductor Canal Blocks Improve Pain Control After Total Knee Arthroplasty?

Conditions
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Knee Arthroplasty

Intervention / Treatment
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* Drug: Magnesium Sulfate
* Drug: Ropivacaine
* Other: Sham


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: American Society of Anesthesiologists classification score of 1 to 3 Presenting for unilateral primary total knee arthroplasty age 18 to 85 Exclusion Criteria: inability to use a patient-controlled analgesia pump long-standing use of opioid medications (3 months or longer) history of chronic pain syndromes significant cardiovascular disease medical conditions that preclude the use of a regional anesthetic technique or any of the study drugs inability to read and understand English incompetent to give consent to study participation women who are pregnant or nursing

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 85 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Magnesium<br>Participants in this arm will receive magnesium sulfate + ropivacaine via adductor canal block | Drug: Magnesium Sulfate<br>* Given via adductor canal block<br>* Other names: Sulfamag, Epsom salt, Health Canada DIN: 02139499;Drug: Ropivacaine<br>* Given via adductor canal block<br>* Other names: Naropin;|
| Active Comparator: Non-magnesium<br>Participants in this arm will receive ropivacaine via adductor canal block | Drug: Ropivacaine<br>* Given via adductor canal block<br>* Other names: Naropin;|
| Sham Comparator: Sham<br>Participants in this arm will receive a sham adductor canal block | Other: Sham<br>* Sham adductor canal block<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Time to first analgesic request | Investigators will note the time lapsed between end of surgery and the first request for additional analgesia (given using patient controlled analgesia pumps, as is standard of care at the study institution). | First occurrence during hospitalization (up to 72 hours postoperatively) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cumulative morphine consumption | Patient-controlled analgesia pumps allow the investigators to measure how much morphine each patient requests. | Cumulative dose during the first 24 postoperative hours | 
| Number of steps taken | The investigators will record the number of steps each patient takes during postoperative days 1 and 2 in hospital. | Number of steps taken during postoperative days 1 and 2 | 
| Pain | Pain scores will be assessed using a visual analog scale at each of the above times. | 2, 4, 8, 12, and 24 hours after adductor canal injection (or sham) | 
| Patient satisfaction | Patients will rate their satisfaction with their analgesia using a scale from 1 to 5. | Once, 24 hours after surgery | 
| Time to readiness for discharge | The time at which each patient reaches the criteria for discharge readiness determined by physiotherapy using an assessment checklist will be recorded. | Once, upon occurrence, within 72 hours after surgery | 
| Length of stay | The length of hospital stay after surgery will be recorded for each patient | Once, within 72 hours after surgery | 
| Side effects | The incidence (presence/absence) of morphine-related side effects such as nausea, vomiting, itching, and respiratory depression will be recorded. | Upon occurrence, up to 72 hours after surgery |