continuous adductor canal blocks vs. low dose femoral nerve blocks for early rehabilitation after total knee arthroplasty

Conditions: Pain, Postoperative; Total Knee Arthroplasty (TKA)

Summary: recently, several articles have suggested or reported that adductor canal blocks (acbs) offer adequate or equal analgesia and may promote better performance in early rehabilitation following total knee arthroplasty (tka) when compared to the more commonly used femoral nerve block (fnb). a common feature of these studies has been the use of moderate to high concentration local anesthetics (e.g. 0.2% or 0.5% ropivacaine respectively) which when injected by a large motor nerve will inevitably cause weakness. however, the practice at our institution has long been a continuous femoral nerve block (cfnb) with a lower concentration local anesthetic (0.0625% bupivacaine). over the past several years the investigators have performed several thousand cfnbs using this technique which has offered the advantage of minimal motor weakness and adequate analgesia. the primary goal of this study is to determine if our established practice of using a low concentration continuous fnb inserted about 5cm caudal to the groin crease (the apex of the femoral triangle) using a low infusion rate of 2ml/hr is comparable to the emerging practice of inserting a continuous peripheral nerve block (cpnb) in the anatomic adductor canal (ac) - infusing at 4ml/hr. a secondary goal is to study the effect of cumulative volume of local anesthetic infused through a fnb when at a rate of 2ml/hr compared to a rate of 4ml/hr in the 48-hour postoperative period. definitions of the location of the adductor canal are debated heavily in literature, but they seem to agree that the middle 1/3 of the thigh contains the proximal ac while the distal 1/3 of the thigh contains the adductor hiatus - the terminal end of the ac. our study will require placement of the continuous acb no more distal than 20cm cephalad to the superior pole of the patella due to placement prior to surgery and the need to keep the dressing out of the operative field. the cacb catheter will also not be placed any more proximal than 20cm distal to the asis. in addition to other exclusion criteria, these measurements will create an exclusion for patients with an iliac-to-patella distance less than 40cm. iliac to patella distance (ipd) will be measured at the pre-operative interview on the day of surgery with a measuring tape. external palpable landmarks of the anterior superior iliac spine and the superior pole of the patella will be used. the primary outcome is based upon the ability to perform rehabilitation exercises postoperatively to the extent that criteria for discharge can be met. the primary outcome measured is the time at which a patient gains the ability to successfully perform a 75-feet unassisted walk. on the day of surgery (dos), prior to any walking attempt, a secondary outcome measure will be to perform a 5-second sustained straight leg raise. other secondary outcomes will be the number of days admitted prior to discharge, and average pain scores on dos, postoperative day (pod) #1, and pod#2. the day of discharge will also be used as a secondary outcome. earlier discharge is becoming a goal of almost all healthcare systems to minimize costs.

the three arms are as follows: 1. the control group; continuous femoral nerve block - low dose (cfnb-ld) will be patients randomized to our standard therapy comprised of a low dose/concentration continuous femoral nerve block inserted approximately 5cm distal to the groin crease with a rate of 2ml/hr. 2. higher dose (hd) cfnb; - block placed in same location as cfnb-ld but with a higher dose rate of 4ml/hr. this higher rate could afford more pain control but may cause more quadriceps or hip flexor weakness. 3. continuous adductor canal block (cacb) group will have a catheter inserted 20-30cm proximal to the superior pole of the patella, and an infusion rate of 4ml/hr, but with similar dressing to make it appear like those in group 1 and 2. acute pain/regional anesthesiologists and fellows will be performing all research procedures in the same locations that the investigators routinely perform regional nerve blocks: our preoperative holding area adjacent to the operating room suites at university of pittsburgh medical center (upmc) - passavant. all three groups have a set rate that will not increase. there also will be no bolus orders given on the floors, however iv and po medications will be available to decrease discomfort. these medications are ordered to be given upon request (prn); upon patient request. down-regulation of doses will also not be allowed as that would cause uncertainty as to which regimen may contribute most to postoperative weakness. the only adjustment allowed will be to turn off the nerve block infusion completely on pod #1 if a dense motor block of the quadriceps or iliopsoas (hip flexor) exists, as this condition does not facilitate participation in rehabilitation exercises. the frequency of early-removal of nerve block will be recorded for all three groups. cfnb groups continuous femoral nerve block placement: the skin of the right or left groin will be sterilized and draped under sterile conditions, the femoral nerve will be identified using ultrasound just below the inguinal crease and the local anesthetic will be infiltrated subcutaneously. the needle is inserted at the lateral edge of the probe and directed toward the nerve using ultrasound assistance. when in proximity of the nerve, 15ml of 0.2% ropivacaine will be injected through the needle with repeat aspiration every 5 ml. the nerve block catheter will be placed 3-5 cm past the needle tip and secured with steri strips and bio-occlusive dressing. cacb group continuous adductor canal block placement: the distance from the asis to the superior pole of the patella will be measured and the distance recorded. this iliac-to-patella distance (ipd) will be divided into proximal and distal halves, and the halfway point marked. the length of the ipd will need to be a minimum of 40cm for inclusion. the insertion site will need to be 20cm proximal to the superior pole of the patella and at least 20ml distal to the asis. the attending anesthesiologist / acute pain attending either perform or supervise regional anesthesia fellows to place the cacb no more proximal than the halfway mark of the ipd. for example, if a patient has an ipd of 50cm, the halfway mark will be at 25cm and this would be the site of insertion as it would be within the anatomic adductor canal and would be adequately removed from the surgical site. the skin of the right or left anterior-medial thigh will be sterilized and draped under sterile conditions. the sartorius muscle and femoral artery will be identified by an ultrasound at the marked ipd-halfway-mark. there, local anesthetic will be infiltrated subcutaneously. the needle is inserted in the direction of the hyperechoic nerve and the hypoechoic femoral artery using ultrasound assistance. when the needle tip is deep to the sartorius and in proximity of the artery, 15ml of 0.2% ropivacaine will be injected through the needle with repeat aspiration every 5 ml. the nerve catheter will be placed 3-5 cm past the needle tip and secured with steri-strips and bio-occlusive dressing. the cacb rate will be 4ml/hr of bupivacaine 0.0625%. by design, observers should only be aware of a singular kind of patient; those with cpnbs. the dressing of the cacb will be very similar to the cfnb and the standard yellow connector piece will be secured to the skin with bio-occlusive covering, and the location will be at level of the anterior superior iliac spine (asis). this standardized dressing will serve to aid in blinding the observers as to which kind of continuous block the patient received. labeling of the catheter and dressing will not differ. the nerve block billing record will contain the information on the particular approach used. sciatic nerve block placement: the corresponding right or left gluteal area will be sterilized and draped under sterile conditions, the sciatic nerve will be identified by an ultrasound in the lower gluteal region where a local anesthetic will be infiltrated subcutaneously. a trans-gluteal approach will be used to inject normal saline through the needle to assist catheter placement; the catheter will be introduced for 3-5 cm past the needle tip and secured with steri strips and tegaderm. no local anesthetic will be administered until the postoperative period.

Eligibility criteria:
inclusion criteria: * able to consent to regional anesthesia and having primary total knee arthroplasty/replacement exclusion criteria: * body-mass index \>40 * iliac to patella distance (ipd) \<40cm * pre-existing quadriceps weakness of involved surgical side chronic opioid use (if using opioids within 4 weeks of surgery: excluded)

Keywords: continuous femoral nerve block continuous adductor canal block