Continuous Adductor Canal Blocks Vs. Continuous 'Very-Low Dose' Femoral Triangle Nerve Blocks For Early Rehabilitation After Total Knee Arthroplasty
Earlier discharge and return of mobility after Total Knee Arthroplasty (TKA) is a goal of healthcare systems to minimize costs. In a recent series of 509 TKA patients, implementation of motor-sparing, distally-placed femoral apex continuous femoral nerve blocks (CFNB) infusing @ 2ml/hr decreased length of stay. Even more cost-significant, the motor-sparing practice decreased the number of patients being discharged to non-home dispositions.1
A feature of studies finding the use of Adductor Canal Blocks (ACB) superior to FNB is the use of large volume initial boluses (30ml) of moderate to high concentration local anesthetics (0.2%, 0.5%, and 0.75% Ropivacaine) at the inguinal location.2,3,4 This invariably causes quadricep and hip flexor weakness.
Alternatively, using CFNBs with a low volume initial bolus (15-20ml) and a continuous infusion of a lower concentration local anesthetic (0.0625% Bupivacaine) @ 2ml/hr is the standard practice at the investigator’s institution. The hypothesis is that these “very-low dose CFNBs” provide motor-sparing effect comparable to a continuous ACB, and thus should not delay discharge nor increase total cost of the episode of care.
Materials and methods
Approval by the institutional review board was obtained prior to trial initiation, and informed consent was obtained for all enrolled patients. The study was registered with www.clinicaltrials.org.5 Exclusion criteria were: age >75 years, BMI >40, short femur length -'Iliac-to-Patella distance' <40cm, pre-existing myopathies, revision and bilateral TKA.
TKA patients must be able to walk independently prior to discharge. Thus, the primary outcome of the study is the number of hours after surgery at which a patient gains the ability to successfully perform a 75-feet unassisted walk with a wheeled walker just as they must do after post-acute care discharge.
The length of stay (in hours after surgery) was used as a secondary outcome.
63 patients were randomized into three groups between June 2015-August 2016
1. The control group; CFNB - Low Dose (CFNB-LD) : Patients received standard TKA therapy utilized at UPMC-Passavant Hospital: CFNB inserted approximately 5cm distal to the groin crease with a rate of 2ml/hr.
2. Higher dose (CFNB-HD); - same location as CFNB-LD but a higher rate of 4ml/hr. This higher rate used to afford more pain control but may cause more weakness.
3. Continuous Adductor Canal Block (CACB) group - rate of 4ml/hr, but with similar dressing to make it appear like those in groups 1 and 2.
No additional local anesthetic was given in recovery to avoid variability.
All three groups received a continuous trans-gluteal nerve block in addition to the assigned anterior thigh nerve blocks. This was performed with the purpose of avoiding posterior knee pain which, in our experience, occasionally occurs and limits rehabilitation.
There was a trend toward decreased median LOS for CACB patients, however it was not clinically significant. Mean LOS was only 2 hours less than for CFNB. See Tables 1 and 2.
Using CFNBs placed distal to the inguinal ligament with a lower rate/concentration does not delay time to discharge readiness nor time to discharge compared to CACBs.