Blocking sensation from the femoral nerve by injecting local anesthetic around the nerve
plays an important role in pain control after total knee replacement. However, femoral nerve
block has been associated with increased risk of falls due to weakness of the thigh muscle.
This prospective, randomized controlled trial asks the question whether blocking the more
distal branch of the femoral nerve (saphenous nerve) will result in less muscle motor block,
and thus less risk of falls. The study also aims to compare pain control after both
If the patient is willing to participate and signs the consent, he/she will be randomized to
one of the two treatment groups:
1. Femoral nerve block
2. Adductor canal block
The standard of care anesthesia regimen for this surgery is as follows:
All Patients will receive their Multimodal Perioperative Pain Protocol (MP3) medication as
per routine care in the patient receiving area. All blocks are performed in the
pre-operative holding area with standard ASA monitors applied. Typically, patients receive
1-2 mg of midazolam and 50-100 mcg of fentanyl for sedation during the placement of the
block. Standard operating procedure of the block room will be followed. Block time out will
be preformed according to standard operating procedure. All blocks will be done under
ultrasound guidance. Sonosite (S nerve) machine will be used with a high frequency linear
(HFL) US probe with 6-13 MHZ frequency. Both CFNB and ACB will take be performed according
to the SOP in the investigators department.
For CFNB: Images of the femoral nerve will be obtained in the short axis. 1% lidocaine will
be used for local infiltration of the skin. A 2 inch 18 G touhy needle ( B Braun) will be
advanced in plane under US guidance . Confirmation may take place with Quadricpes muscle
twitches and patella movement between 0.3 and 0.4mA (2Hz; 0.1ms). A bolus of 20 ml of
Ropivicaine 0.5% will be injected. A non stimulating catheter will be advanced through the
needle to a distance of 3-4 cm beyond the needle tip. Catheter will be secured in place
using benzoin, Steristrips, and a tegaderm.
For the ACB: ultrasound survey at the medial part of the thigh will take place, halfway
between the superior anterior iliac spine and the patella. In a short axis view, the femoral
artery will be identified underneath the sartorius muscle, with the vein just inferior and
the saphenous nerve just lateral to the artery. The needle will be introduced in-plane and 2
to 3 mL of LA bolus (0.2% ropivicaine) will be used to verify correct placement of the
needle in the vicinity of the saphenous nerve in the adductor canal. A bolus of total volume
of 20 ml of Ropivicaine 0.5% will be injected through the needle. The catheter will then be
introduced and advanced 2-3 cm beyond the tip of the needle.
At the conclusion of surgery a large obaque dressing will be applied from the femoral crease
to the mid thigh region so that the catheter location will be concealed. Both catheters will
be connected to a pump that will infuse local anesthetic. Ropivicaine 0.2% at 8 ml/hour.
There is usually a period of time before the patient transport to the operating room during
which the investigators will be able to evaluate if the block is effective and sufficient
Patients will receive either general or spinal anesthesia in the operating room. All
patients will receive prophylaxis for nausea and vomiting during surgery. Regimen for
prophylaxis include a single dose of dexamethasone after induction of anesthesia and a
single dose of Ondansetron 20 minutes before recovery from anesthesia. This study is not
deviating from the standard of care anesthetic regimen for this surgical procedure at Penn
Presbyterian Medical Center. Only the type of blocks will be different between the two
Postoperative analgesia All PACU analgesia will follow standard of care protocol for post
operative care at PPMC. Hydromorphone 0.2 mg iv q5 minutes as necessary. The infusion of the
local anesthetic will start in the PACU.
In the PACU, patients are assessed for pain with the Visual Analog Scale (pain scale of 1 to
10) at routine time points for the duration of their stay. The worse VAS score will be
Postoperative analgesia will follow the MP3 protocol. The protocol includes administration
of around the clock acetaminophen, Celebrex, gabapentin, immediate and extended release
- Patients scheduled for primary total knee arthroplasty
- American Society of Anesthesiologists (ASA) physical status I -III
- mentally competent and able to give consent for enrollment in the study
1. Patient younger than 18 years old
2. Allergy to local anesthetics, systemic opioids (fentanyl, morphine, hydromorphone,
and any of the drugs included in the multimodal perioperative pain protocol (MP3).
3. Revision surgery will be excluded.
4. Impaired kidney functions and patient with coagulopathy will also be excluded.
5. Chronic pain syndromes; Patients will be defined to have chronic pain if they are
using regular daily doses of systemic narcotics for the past 3 months prior to the
6. BMI of 40 or more
7. Pregnancy (positive urine pregnancy test result in Preop area on morning of surgery)