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, 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
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
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
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.
- Able to consent to regional anesthesia and having primary total knee
- 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)