Long Lasting PNB for TKA and ACL Surgery

Lake Manyara, Tanzania - photo by JoAnn Sturman

Scott Sturman, M.D.

Some surgeons prefer femoral nerve blocks for post op pain relief following TKA.  Due to quadriceps weakness, physical therapy is not scheduled until the day after surgery.  The femoral nerve block alone does not afford complete pain relief, and patients often require narcotic supplements.  Spinal narcotics may mitigate the incomplete coverage, but nausea, vomiting, and pruritis are a concern.  The following describes a technique which provides extended and complete post op pain relief.

The objective of the block is not to provide surgical anesthesia but rather long lasting post op analgesia with retention of some motor function.  The duration of these blocks is volume dependent and requires the use of 200 mg of .25% bupivacaine with decadron and buprenorphine placed under ultra sound guidance.

The patient, a 78 year old male, received no pre op narcotics.  He underwent femoral and popliteal blocks after receiving fentanyl 50 ug.  Each block consisted of a mixture of 40 ml of .25% bupivacaine with decadron 5mg and buprenorphine .15 mg.  The patient received general anesthesia, and although surgical stimulation was blunted by the block, the reduced local anesthetic concentrations did not provide surgical anesthesia during the osteotomies.  

The patient was pain free and received no narcotics in the recovery room.  Although his leg was numb and lacked normal strength, he was able to move it.  He was transferred to the floor, where he experienced a 37 hour pain free interval. 

The technique has been used for out patient ACL patients, who are discharged with a knee brace.  In this younger group of patients analgesia lasted 30 hours post block.  In these cases .25% bupivacaine prevents most surgical surgical stimulation, so patients receive the added benefit of being carried on less than 1 MAC anesthesia.

 Iguasu Falls, Argentina - photo by JoAnn Sturman

 

High Popliteal Block

 Peacock of Australia - photo by Tom Yanagi, M.D.

by Andrew Wall, M.D.

Patient positioning may be an obstacle when performing lower extremity peripheral nerve blocks, especially of the sciatic nerve.  Traditionally, the sciatic nerve is blocked in the lateral decubitus position for a subgluteal approach or prone for a popliteal approach.  This requires repositioning a heavily sedated patient on a narrow gurney or operating room table, which is often cumbersome and time consuming.

One solution for below the knee surgery is a popliteal block in the supine position with a saphenous supplemental block via the subsartorial approach.  This combination may be done quickly in the supine position with minimal position change.

The lower extremity is positioned with the hip flexed approximately 30 degrees.  The lower leg is supported with a Ferkle device which allows for adequate access to the popliteal area.   While seated, place the probe on or slightly superior to the popliteal crease and locate the popliteal artery, tibial and common peroneal nerves.  The nerves will be superficial and lateral to the vessels.  If the nerves are hard to visualize, have the patient dorsiflex and plantarflex.  The tibial and peronial nerves move with this maneuver.  Trace the structures cephalad until the nerves merge, usually 7-10cm above the crease.  Needle entry will be in the crease between the vastus lateralis and bicpes femoris.  This is different than other PNB approaches where entry is next to the probe.

Sciatic Nerve Block

Rest your “probe arm” elbow on the bed, this adds stability and prevents the probe from sliding as your muscles fatigue.  When injecting local in the skin and soft tissues, be sure to glance up at the screen to make sure you are on the right trajectory.  It can be tricky at first because directions are reversed.  For example, steepening the angle moves toward the top of the screen – not away from it.  The structures are deep using this approach so a 4 inch needle is mandatory.  If the patient is especially large a curvilinear probe may be preferable.  Inject 30cc of the local of choice; circumferential spread is desirable.

Saphenous Nerve Block

Next, externally rotate the leg onto the bed exposing the inner thigh.  Prep the skin from mid-thigh to knee and use the linear (curvilinear for large patients) probe to identify the SFA under the sartorius muslce just medial to the vastus medialis.  This artery dives deep to become the popliteal. Before doing so, it gives off the genicular artery.  The saphenous nerve runs with the SFA and continues superficially with the genicular.  The nerve is not always visible, but the artery should be, and they share a fascial sheath.  Inject 10-15cc of local in this plane to supplement the saphenous distribution of the lower extremity.  Less local is required because of the size of the nerve. 

This regional block combination allows one to use less local than the traditional femoral/popliteal combination.  Since the saphenous nerve is strictly sensory there is no quad weakness.  On the downside, this approach to the saphenous nerve is less reliable (60-80%) than a traditional femoral nerve block.  Therefore, if using a “regional only” technique a femoral/sciatic is probably necessary.

The following hyperlink provides an excellent illustration of the anatomy for the saphenous nerve block:

Sub-Sartorial Nerve Block Illustration

Madera, California - photo by Tom Yanagi, M.D.