A popliteal plexus block is a type of regional anesthesia specifically designed to numb the lower leg and foot. This procedure involves injecting a local anesthetic near specific nerves, temporarily blocking pain signals from reaching the brain. It offers a way to manage pain and sensation in a targeted area of the body.
Understanding the Popliteal Plexus Block
The popliteal plexus block targets the sciatic nerve, a large nerve that runs down the back of the leg. In the popliteal fossa, the diamond-shaped space behind the knee, the sciatic nerve divides into two main branches: the tibial nerve and the common peroneal nerve. These two nerves provide motor and sensory innervation to most of the lower leg, ankle, and foot.
By administering local anesthetic around these nerves, sensation and muscle movement in the areas they supply are temporarily interrupted. This results in numbness and pain relief below the knee, excluding the medial aspect of the lower leg, which is supplied by the saphenous nerve. The block’s effect is similar to a more proximal sciatic nerve block but spares the hamstring muscles, allowing for knee flexion.
Common Applications
A popliteal plexus block is used for surgical procedures involving the foot, ankle, and lower leg. These include corrective foot surgeries, Achilles tendon repair, foot debridement, and procedures for foot fractures or dislocations. This regional anesthetic technique serves as the primary anesthetic for these operations.
Beyond surgical anesthesia, a popliteal block is administered for post-operative pain management. It provides significant pain relief for several hours, reducing the need for strong systemic pain medications like opioids. This leads to decreased side effects such as nausea and vomiting, and facilitates earlier discharge from recovery units.
The Administration Process
The administration of a popliteal plexus block begins with patient positioning, on their stomach or side with the hip and knee flexed. A medical professional, usually an anesthesiologist, will prepare the injection site with antiseptic solution to maintain a sterile environment.
Ultrasound guidance is used during the procedure to enhance accuracy and safety. Ultrasound allows visualization of the sciatic nerve, its branches, and surrounding structures like blood vessels in real-time. A small needle is then advanced towards the nerve, and a nerve stimulator may also be used to confirm precise needle placement by observing a motor response in the foot or calf at a low current. Once the needle is in the correct position, a local anesthetic, such as ropivacaine or bupivacaine, is slowly injected around the nerve. The injected volume, typically 15-20 mL, aims for adequate anesthetic spread around the nerve within its sheath.
What to Expect During and After the Block
During the administration of the popliteal plexus block, patients may feel a sensation of pressure or a brief sting as the initial numbing medication is given. As the needle approaches the nerves, some may experience a tingling sensation or mild discomfort, particularly if they are awake or lightly sedated during the procedure. These sensations are temporary and indicate the needle is near the target nerve.
After the local anesthetic is injected, numbness and weakness in the lower leg and foot gradually develops. The onset of numbness varies, but a complete sensory and motor block is achieved within 19 to 26 minutes with ultrasound guidance. Block duration depends on the anesthetic type; shorter-acting agents provide 30 minutes to an hour of relief, while longer-acting ones, like bupivacaine or ropivacaine, last 12 to 36 hours. As the block begins to wear off, a sensation of pins and needles may be felt, followed by the gradual return of normal sensation and motor function over several hours.
Important Considerations
While popliteal plexus blocks are considered safe, there are considerations for patients. Rare side effects include temporary nerve irritation, manifesting as prolonged numbness, tingling, burning, or weakness resolving within 4-6 weeks. Bruising at the injection site is possible.
Rare complications include infection or more significant nerve damage; major complications, such as prolonged sensory or motor deficits, are reported in less than 1% of cases. Modern techniques, especially ultrasound guidance, have improved safety and success rates. Following post-procedure instructions is important, such as protecting the numb limb from injury due to lack of sensation. Patients should also manage pain as the block wears off with prescribed oral painkillers. Contact a healthcare provider if persistent numbness, weakness, or unusual pain occurs.