Overview of Below-Knee Amputation
A lower-extremity amputation is a surgical procedure performed to remove a part of the lower leg that is not viable or healthy. Non-viable tissue can be caused by several things, including lack of blood supply (ischemia), infection, injury, or cancer. Removing the unhealthy tissue can sometimes be a life-saving procedure. Most of these amputations are due to leg ischemia, peripheral arterial disease, and diabetes, accounting for more than 50% of cases. Injuries are the next most common cause of lower-extremity amputations.
An international group of experts known as the TransAtlantic Inter-Society Consensus (TASC II) reported that every year, up to 50 out of 100,000 people undergo major amputations due to a disease called peripheral artery disease, which affects the blood vessels outside the heart.
Although the rates of lower-extremity amputations have decreased recently, about 3500 amputations related to injuries are still performed every year in the United States. Despite being a challenging procedure with significant health impacts, lower-extremity amputation remains critically important; it can greatly improve the quality of life and even save lives when indicated.
Ernest M. Burgess, a physician, was the first to describe the amazing functional benefits of preserving as much of the tibia (the larger bone in the lower leg) as possible during an amputation.
Anatomy and Physiology of Below-Knee Amputation
The lower leg contains four compartments which hold the muscles responsible for foot movement, as well as important blood vessels and nerves. Understanding this separation is key for surgery involving the leg, including every situation from controlling blood loss to mitigating potential complications.
The front compartment, which is next to the larger of the two lower leg bones (the tibia) and in front of the smaller one (the fibula), contains specific muscles that allow for foot movement, as well as the deep nerve and blood vessels of this area. Notably, the blood supply to this area comes largely from the anterior (or front) tibial artery, with help from the peroneal artery.
The side compartment lives just behind the front compartment and beside the fibula. Here, you’ll find more muscle and another nerve that courses through for a good bit of its journey. This compartment is supplied by the branches of the peroneum artery.
The back compartment, divided into two parts, is home to the muscles that make up your calves. Some of the tibialis posterior (inner calf muscle), along with the big- and small-toes flexors, rest within the deep part, alongside other essential nerves and blood vessels in the leg. The blood supply mainly comes from the posterior (or back) tibial artery. This is key because a surgeon will base the skin flaps for amputations on how the blood flows to the foot.
The blood supply below our knees mainly comes from the popliteal artery, which branches out to a series of arteries called tibial arteries. Also supplying the tibia (or the main bone in the lower leg) area with blood are branches from the anterior tibial artery for the start of both the shaft and end of the tibia. Further down the tibia, the posterior artery starts to supply blood to the end, which is important to note because surgeons often use this part of the leg when reconstructing the jaw bone. The blood from here is drained through veins of similar names and towards the vein found behind the knee.
Tissue fluid or lymph also drains from the tibia and fibula into the lymph nodes located in the groin area. The nerve supply to this section of the lower leg primarily comes from the nerves in the same area, but they lead to a few other places as well such as the upper leg and the foot.
Understanding the muscles that have their starting or ending points on the tibia is also important – the tensor fasciae latae, quadriceps femoris, sartorius, gracilis, semitendinosus, horizontal head of semimembranosus muscle, popliteus, tibialis anterior, extensor digitorum longus, soleus and flexor digitorum longus are all significant examples. Each of these muscle attachments is situated differently on the tibia, with some at the top, bottom, front or back of the bone.
The fibula, the other bone in our lower leg, is connected to another set of muscles – with the biceps femoris, fibularis longus and brevis, extensor digitorum longus and extensor hallucis longus, and fibularis tertius all having associations with the fibula and inserting at various points along it.
Why do People Need Below-Knee Amputation
A below-the-knee amputation (BKA) is a surgery where the doctors remove the lower part of your leg. Doctors will decide to perform this surgery in three main situations: urgent or emergency cases, failed attempts to save the leg, and non-emergency or elective cases.
In urgent cases, the problem might be a severe infection or a serious injury. Here, the infection or injury is spreading so rapidly that it poses a risk to life. So, the doctors need to remove the bad part of the leg immediately, sometimes even by the bedside if there isn’t enough time to go to the operating room. Before surgery, if there’s some time, they will try to use antibiotics to control the infection as much as possible. Once the infected part of the leg is removed, if possible, doctors might try to restore blood flow to the remaining part of the leg to promote healing.
BKAs can also be done in cases where previous treatments attempting to save the lower leg have failed. This could happen if the leg has been severely crushed or burned, if blood flow or nerve signals have been completely cut off, or if there are significant skin and tissue injuries that can’t be repaired. Before the doctors decide to go ahead with the amputation, they will assess if you’re stable enough for the surgery. They will do this by checking various factors including your heart rate, blood pressure, blood test results, and any other injuries you might have.
Lastly, there are elective BKAs. This is when the surgery isn’t an emergency and is done in patients who do not have a severe infection in their leg. This might be needed if a person has a leg wound that isn’t healing, if multiple surgeries to remove small parts of the foot haven’t solved an ongoing infection, if there was a problem with blood flow that couldn’t be fixed and now there’s an ulcer that’s not healing, or if the foot or ankle no longer function and there’s ongoing pain that can’t be treated.
When a Person Should Avoid Below-Knee Amputation
For people considering a non-emergency below-the-knee amputation (BKA), poor blood flow to the area where the surgery is planned can be a serious concern. In cases like this, we can’t go ahead with scheduled or semi-urgent procedures until the blood flow is better. To make sure blood flow has improved enough, we need to check the person’s health carefully before surgery. This includes measuring changes in blood flow in both lower limbs.
We can use a tool called a Doppler to assess overall blood flow, and tests called ankle-brachial indices to compare blood flow in the lower and upper limbs. We also measure oxygen levels in the toes and the skin’s oxygen pressure to work out how well the smallest blood vessels are working. When the blood flow is very poor, the person might need additional treatment, like a bypass graft or stent, before the BKA can take place. Some scientists have even used a special imaging technique with a dye called indocyanine green to predict issues after surgery, like skin flap necrosis (death of skin tissue).
It’s also important to make sure a person is stable enough for major surgery. This applies especially to people who are critically ill due to things like severe infections, massive blood loss, serious organ failure, or other causes. We should do everything we can to stabilise these patients before starting a major operation. An exception to this rule is if the person has a rapidly spreading infection that is causing tissue death, where controlling the infection can be life-saving. And for patients with severe bleeding, we might apply a tourniquet (a device that stops blood flow) for a few hours to help stabilise their condition.
Equipment used for Below-Knee Amputation
To perform any orthopedic surgery, having a standard set of surgical tools is crucial. Necessary tools include a tourniquet, special imaging technology called fluoroscopy, a large knife used for amputation, a bone saw that can oscillate or move back and forth, a drill and bit to attach muscle to bone edges, silk threads for stitching, a rongeur (a surgical tool used for cutting and trimming bone), and a suction drain.
The patient is prepared and covered while lying flat on their back. A small lift is put under the side of the patient’s hip that needs surgery. This rotates the leg inward so that the knee and ankle are pointing upwards. A tourniquet, a band used to stop blood flow, is placed as high as it can go above the knee. This allows the doctors to clean and expose as much of the leg as possible. Alternatively, a sterile tourniquet might be put on after the patient is covered with a sterile drape.
Who is needed to perform Below-Knee Amputation?
To carry out a BKA (below-knee amputation) safely, a typical team of surgical experts is necessary. This team includes the operating surgeon, who will be in charge of the procedure, an anesthesiologist who helps manage your pain and keeps you unconscious during the operation, a scrub tech who assists the surgeon by providing necessary surgical tools, and a circulator who makes sure everything runs smoothly in the operating room. Due to the complexity of working around a lower limb and managing the operation safely and effectively, it’s notably beneficial to have the help of additional surgical assistants if they’re available.
Preparing for Below-Knee Amputation
Before having any kind of surgery, it’s important to check your overall health. This involves looking at various parts of your body, including your blood, to make sure that you are in the best condition to heal after the operation. Doctors can check things like your levels of prealbumin, albumin, glycosylated hemoglobin, and total lymphocyte count to make sure your body has what it needs to recover. They will also have a look at any existing injuries or conditions that might affect the operation, for example, if you have any neuropathy, which is a type of nerve damage.
If your surgery is related to a severe wound or injury, your doctor will also closely examine the tissue around the injured area. In some situations, especially after a severe injury, they might have to wait a few days to see how well the wound is healing before deciding the best way to proceed with surgery.
For cases involving an infection, you might need to have a special kind of scan called an MRI. This powerful scan can show things like osteomyelitis, which is a type of bone infection, and if there’s any buildup of fluid around your tissues. Other tests like an ultrasound can also be used to look for pockets of fluid. Blood tests are also important for detecting and understanding the extent of an infection in your body.
Pictures – or what doctors call imaging – are very important before deciding the best way to go ahead with surgery. They help doctors see the inside of your body, including your bones, and other structures like your foot, ankle, and knee. These images help doctors look for any other health problems, like a fracture, or air beneath your skin. An MRI, in addition to showing bone and fluid issues, can also show whether your body tissues are healthy and ready for surgery. For example, if you had an injury that caused your skin to peel away from the underlying tissue, an MRI could help your doctor decide what kind of operation is best for you.
How is Below-Knee Amputation performed
There are two main ways to do a below-knee amputation (BKA), which is an operation that involves removing part of the leg below the knee. The first method is known as a guillotine amputation, and the second method is referred to as a completed amputation.
In a guillotine amputation, the procedure is performed quickly to control infection or blood loss, especially when an extremity is severely damaged. This type of amputation is used when tissue needs a few days to heal and be cleaned before closure. On the other hand, a completed amputation involves closing and suturing the stump in one go, which is viable when there is ample time and tissue available. This leads to a closed amputation site ready for fitting a prosthesis (artificial limb).
When the patient is prepared for surgery, the surgeon marks the site where the amputation is going to occur. They then make an incision on the front and back of the leg, ensuring that the back incision is larger to enable enough skin for closure after amputation. Using a special surgical knife, the surgeon cuts through the skin, fascia (connective tissue), and muscles in the leg before identifying and treating the nerves and arteries in the area. Then, the bones (tibia and fibula) are cut and reshaped.
In a certain method known as the “Ertl” technique, the surgeon creates a bony bridge between the two cut bones (tibia and fibula) to provide a stable, weight-bearing surface for better function of the prosthesis. Once the procedure is complete, the wound is closed up by approximating (bringing together) the different layers of tissue and finally, the skin. The surgeon may use either stitches or staples—this usually depends on their preference.
Once the amputation is complete, the leg stump is covered with a sterile dressing and placed in a supportive splint or immobilizer for protection and healing. It also helps prevent early bending contractions at the knee that might limit mobility with a prosthesis in future.
Post-surgery, the stump should be checked regularly for signs of skin decay, bleeding, or infection. If a drain was used, it would be removed once there’s sufficiently minimal drainage. When the wound is healing well, a stump shrinker (a compression garment) can be used to maintain the size and shape of the stump. Finally, the patient can begin the process of being fitted for a prosthetic limb depending on their preference, condition, and what their insurance covers.
Possible Complications of Below-Knee Amputation
Like any surgery, there can be acute, or immediate complications following the operation. These can include issues like uncontrolled bleeding, infection, severe postoperative pain, and other medical problems such as deficiency of red blood cells due to acute blood loss and a sudden reduction in the blood supply to the heart. A second operation might be needed if a below-the-knee amputation (BKA) was performed due to infection or acute tissue damage, and the area of infection was not completely removed or if the edges of the skin further demarcate, meaning that the healing isn’t progressing as expected.
There can also be chronic, or long-term complications from below-the-knee amputations. One of these is the development of painful growths of nerve tissue (neuromas) which can result from nerves being cut during surgery. This highlights how crucial it is for the surgical procedure to be done correctly.
Many people also experience phantom limb pain – this is a sensation where it feels like the limb that was amputated is still there and causing pain. This can be addressed in various ways, including a mirror box which tricks the brain into thinking the limb is still there, local injections, adjusting the artificial limb (prosthesis), or using different therapies designed to help with this type of pain.
It’s also important to remember the mental and emotional impact of undergoing an amputation. Patients may experience depression or even suicidal thoughts. Hence, mental health support is crucial after the operation.
What Else Should I Know About Below-Knee Amputation?
Undergoing a below-knee amputation (BKA) can be life-saving in severe illness or injury. It can also greatly improve a person’s quality of life, for example, in cases where folks have severe foot ulcers that don’t heal and make it hard to walk. By removing the infected limb and fitting a prosthesis (artificial limb), patients can regain their ability to move around.
People who experience chronic pain from a lower body injury might also have a BKA. This operation can give them relief from pain and allow them to function better, resulting in satisfactory results. However, it’s key to know that after a BKA, a person’s energy needs during walking will increase. The extent of this increase depends partially on how well the muscles in the remaining part of the lower limb are maintained after surgery.
Therefore, getting a BKA is a big decision, especially for elderly or frail individuals. They should consider their overall health and mobility and should also seek nutritional advice. It’s also important to note that some groups, like those with advanced diabetes who get a BKA for foot ulcers, have been found to live, on average, about three years after the operation.