Magnesium Sulfate in Adductor Canal Blocks
Condition: Knee Arthroplasty
Study type: Interventional
Phase: Phase 4

Summary: 
      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: 
      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.
    

Intervention name(s): Magnesium Sulfate; Ropivacaine; Sham
Intervention type(s): Drug; Drug; Other
Intervention description(s): Given via adductor canal block; Given via adductor canal block; Sham adductor canal block
Other intervention name(s): Sulfamag, Epsom salt, Health Canada DIN: 02139499; Naropin
Intervention MeSH terms: Magnesium Sulfate; Ropivacaine
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment