One of the main concerns many patients have when undergoing knee and hip replacement is pain after surgery. Because patients are so different, it can be challenging to manage pain adequately with one standardized method. Often, multiple methods of pain management –before, during, and after surgery – may be necessary to facilitate healing. A femoral nerve block is an effective way to moderate pain immediately following total knee and hip replacement surgery. Femoral nerve blocks can be used in addition to any surgical pain management with very few side effects or complications.
What is a femoral nerve block?
A femoral nerve block is a type of anesthesia most often used for pain management after total knee and hip replacement surgery. This type of selective nerve root block is administered as a one-time injection or delivered steadily as a continuous femoral nerve block (CFNB) via catheter. It can be administered on its own to target a specific area of the thigh and knee or combined with a sciatic nerve block to achieve complete numbness of the lower leg.
The femoral nerve is the largest nerve that originates from the lumbar spine from three vertebrae: L2, L3, and L4. Its complicated path takes it through the psoas muscle. This muscle is located behind the organs but in front of the spine, deep inside the body.
The nerve then moves downward between the psoas and the iliacus, a flat, triangular muscle inside the hipbone. These muscles are often referred to as the iliopsoas because they both attach at the upper inner thigh and work together. The femoral nerve is intertwined with these muscles. It enervates not only these two muscles that move the legs, but also the front and inner sides of the surface of the skin on the thigh and the knee joint.
Unlike a sympathetic nerve block that targets the length of the spine or a sciatic nerve block that is focused on the lower back, buttocks, and entire leg, a femoral nerve block specifically targets the area:
- Across the hip
- Down the front and inside of the thigh
- Around the knee
Sympathetic and sciatic nerve blocks can be great solutions for widespread pain, but the femoral nerve block technique aims to make patients more comfortable after surgery.
How does a femoral nerve block help?
A femoral nerve block for post-op pain management works by disrupting pain signals to the brain. It allows patients to begin the path to recovery by helping them become mobile after surgery without significant pain.
As a diagnostic tool, femoral nerve blocks also offer insight into what the cause of knee pain might be.
Other uses of femoral nerve blocks include:
- Analgesia after femoral fracture
- Evaluation of knee injuries
- Surgeries on the medial (middle) lower leg
What are the benefits of a femoral nerve block?
For total knee replacement surgery, femoral nerve blocks have outcomes that are superior to other types of pain control.
In a review of scientifically-valid studies, researchers found that femoral nerve blocks offered better post-operative pain relief than either opioids or epidural anesthetic. Further, femoral nerve blocks had less nausea and fewer side effects than other pain treatment options.
As an option for post-operative hip replacement pain, femoral nerve blocks have good results with pain management on the inner knee and thigh, but less pain control on the outside of the leg. This makes sense, as the femoral nerve does not enervate that area of the leg. Elderly hip replacement patients in one trial had much-improved post-operative outcomes with femoral nerve blocks.
What should I expect for the procedure?
A femoral nerve block begins well before the actual injection. Here is what to expect before, during, and after your procedure.
Your doctor will give you pre-operative instructions that are specific to your health history and condition, but there are some general guidelines to follow. If they differ from your doctor’s advice, always follow your doctor’s advice first and foremost.
If you take aspirin for a heart condition or blood vessels, talk to your doctor about when to stop taking that. Aspirin is a blood thinner and can cause complications. Plavix, a blood thinner used to treat coronary artery disease and prevent stroke, can also cause complications. Talk to your doctor to see if you should stop taking this as well.
If you take herbal medicines, supplements, fish oil, or vitamin E, stop taking those three days before the procedure, and always tell your doctor the full list of supplements and vitamins you’re taking. The interactions between these types of medicines are unknown in combination with nerve blocks, so it best to give them time to clear the body.
If you are taking anti-inflammatory medicines such as ibuprofen, take your last dose one day before your procedure.
On the day of the procedure, it’s important that you feel well and aren’t experiencing a fever over 100.4°. You should not be taking antibiotics or feeling sick at all. If you are, it may be necessary to reschedule your procedure.
The procedure itself is very simple and typically takes between 15 and 30 minutes.
You will lie on your back, possibly with your hips elevated. The area around the injection site will be thoroughly cleaned and disinfected, and a local anesthetic will be administered.
If you are feeling nervous or are unable to relax, your doctor may offer you a sedative through an IV. If this occurs, you will have various monitors applied to monitor everything from your heart rate to oxygen levels. These are necessary to track your response to the sedative and to keep your safe.
At this point, your doctor will use an ultrasound machine to pinpoint the femoral nerve. Once the nerve is located, they will guide the needle to the nerve and perform the injection. For a continuous femoral nerve block, a catheter is inserted so that the anesthetic can be continually administered.
As noted later in the post, femoral nerve block complications and side effects are exceedingly rare, but you can take some steps to care for yourself after the procedure. Do note that your aftercare instructions may differ greatly if your femoral nerve block coincides with another surgery.
For the first 24 hours, limit strenuous activity. In addition to pain relief you may experience numbness and weakness. If you choose to participate in your usual strenuous activities (e.g., working out), you may be more susceptible to injury and other complications. If possible, avoid driving the day of your femoral nerve block as well. Numbness in the leg may make working the accelerator and brake challenging!
At the direction of your doctor, you can begin taking any prescription medications you were taking before your femoral nerve block. Avoid taking any additional pain medications on the day of the procedure, unless advised to do so by your doctor.
If you experience swelling at the site of injection, this can be treated with ice and rest. Warmth in the area should resolve on its own, generally in just a few hours.
Day after and following
On the day after your procedure, you can begin to incorporate all of your regular activities, including driving and exercise. You may find residual numbness and weakness, so take it slow. Gradually increase the intensity and duration of physical activity under your doctor’s guidance.
If your femoral nerve block was accompanied by total knee replacement or hip surgery, you will find that these naturally limit the things you can do. It is important to follow your doctor’s post-operative instructions to the letter to ensure a swift and uncomplicated recovery.
Regardless of whether or not you had surgery, call your doctor immediately if you have any of the following symptoms:
- Signs of infection including fever, extreme redness, swelling, or discharge at the injection site
- A general feeling of malaise or feeling generally unwell
- Numbness in an area that is not the inner thigh, the front of the thigh, or the knee
Other than infection, these signs may not indicate any complications, but it’s always good to check in if you are feeling unsure.
Are there any femoral nerve block complications?
The risk of femoral nerve block complications and side effects is relatively low, but as with any procedure, they are present.
The nerve block does not work
In some cases, the femoral nerve block may not work. This is one of the most common complications, but it is rare.
There are many options to work with this complication, including placing the block again or using other pain management methods.
Numbness is permanent
This femoral nerve block risk is exceedingly rare.
For the vast majority of patients, even those for whom the femoral nerve block lasts longer than expected, the numbness will eventually wear off. In cases where numbness persists, the numb area may be very small.
Local anesthetic toxicity
When a local anesthetic is administered before placing the femoral nerve block, there is a possibility that it might be accidentally injected into the bloodstream.
This extremely rare risk is also one of the most serious, with the potential to cause heart attack. The anesthesiologist is on hand, carefully monitoring the patient, to prevent this or administer emergency treatment if needed.
Bleeding and infection
Any time the skin is broken there is a chance of bleeding and infection. Following pre-operative instructions and keeping the injection sites clean can help prevent this.
Other side effects
Other femoral nerve block side effects include:
- Extra energy
- Weight gain
- Elevated blood sugar
- Soreness at the injection site
These are normal and considered minor.
When discussing your pain management options with your doctor, you may decide the risks are too much for you and decide against a femoral nerve block. You should never feel pressured to utilize one pain management technique or another; you have many options.
However, for some patients with certain conditions, a femoral nerve block is not a good choice. These conditions include:
- Active infection or sepsis
- Bleeding disorders
- Peripheral neuropathy
Talking to your doctor can help you determine if a femoral nerve block is safe for you.
How long does it take a femoral nerve block to wear off?
The length of time it takes for a femoral nerve block to wear off depends on several factors. Most patients find that one femoral nerve block offers total pain relief for 16 to 24 hours, with some residual numbness for several days following the procedure.
Patients with continuous femoral nerve blocks may find pain relief for longer than that, both while the anesthetic is being administered and for several days after.
If you are facing knee or hip surgery, Pain Doctor has many different pain management options to make you comfortable. Get in touch today to see what works for you!