Below-knee prosthesis is one of the most important prosthetic solutions that help patients regain mobility after the loss of a lower limb, and with advances in design techniques and materials used, patients can adapt to a more independent and flexible lifestyle. Below-knee prosthesis includes multiple types that differ in their design and characteristics according to the patient’s condition and needs, and choosing the most suitable prosthesis requires a thorough understanding of its components, how it works, and the potential challenges after fitting.
What is below-knee amputation, and when is a prosthesis used?
Below-knee amputation (transtibial amputation) refers to the removal of the lower limb starting below the knee joint, including the foot, ankle joint, and part of the tibia (tibia and fibula), where the bones are not removed completely, but partially cut in order to preserve a sufficient portion of the bone to be used as a basis for fitting and supporting the below-knee prosthesis. This type of amputation is often performed for reasons related to blocked peripheral arteries, diabetes, or in cases of severe trauma, and is often considered a life-saving procedure.
Compared to above-the-knee amputation, below-the-knee amputation provides better functional results because it allows the knee joint to be preserved, making it easier for the patient to learn on a below-knee prosthesis later and giving them a better ability to walk. The procedure aims to remove unhealthy tissue, minimize pain, and improve the patient’s quality of life, as in many reconstructive orthopedic surgeries.
It is important to start communicating with a prosthetist early, preferably before surgery if possible, as this specialist works as part of a team that includes the doctor, surgeon, and rehabilitation specialist to plan treatment and determine the most appropriate types of below-knee prosthesis according to the patient’s goals and health status after amputation.
The difference between traditional and innovative prosthetics
Below-the-knee prostheses can be categorized into two main types based on the mechanism of action: Traditional mechanical limbs and smart electronic limbs. The following table shows the fundamental differences between these two types in terms of functional and technical characteristics:
| Comparison | Traditional parties | Smart limbs |
| Mechanism of action | Manual mechanical | Sensor- and processor-based electronics |
| Adapting to Movement | Limited and fixed | Highly reactive to user movement |
| Weight | Often lighter | Slightly heavier due to electronic components |
| The need for energy | No electrical power required | Needs charging or batteries |
| Cost | Less expensive | Highest cost |
| Ease of maintenance | Easy to maintain | Requires more specialized maintenance |
| Suitable category | Elderly or limited activity | Young or active users |
Prosthetic components for below-knee prosthesis
Below-knee prosthesis is made up of several essential components that work together to provide stability, comfort, and restoration of mobility, and each below-knee prosthesis is individually designed to fit the shape of the residual limb and the patient’s daily needs. Components include:
- Socket: The main part that is specifically designed to contain the residual limb, usually made of thermoplastic or composite materials, and distributes the weight and pressure comfortably and evenly.
- Liner: A flexible layer worn directly on the skin before inserting the residual limb into the incubator. It is an important element of comfort and stability, often made of silicone gel, a flexible and soft material that helps absorb shock and reduce friction between the skin and the incubator, which reduces the risk of irritation or ulcers, and helps in partial stabilization of the prosthesis.
- Suspension System: Keeps the prosthesis in place and prevents it from moving while walking.
- Pin-lock system: It has a pin that secures the liner inside the incubator with a mechanical lock.
- Suction system: Relies on a vacuum to create a tight fit between the tip and the incubator.
- Sleeves or belts: Sometimes used as an additional or alternative aid to other systems.
- Shank or Pylon: It is made of light and durable materials such as aluminum, titanium, or carbon fiber, and is available in an Endoskeletal design, which is preferred for easy adjustment, or Exoskeletal for greater rigidity.
- Prosthetic foot: One of the most important components of below-knee amputation prosthetics. Types vary depending on the user’s activity:
- Simple, motionless feet: Suitable for people with limited activity and provide good stability.
- Highly responsive, dynamic feet: Absorb shock and store energy to return it during walking, suitable for active users.
- Multi-axis or electronic feet: Mimic natural ankle movement and adapt to the terrain, used in smart limbs.
- Cosmetic Cover: It is used as desired by the patient to give a more natural appearance without affecting the functionality of the limb.
At the beginning of the rehabilitation phase, an initial type of below-knee prosthesis is used, which is adjustable as the shape of the residual limb changes, and is later replaced by a more accurate and stable final below-knee prosthesis after the size and motor activity are stabilized.
Types of prosthetics for a below-knee prosthesis
There are many types of below-knee prosthesis, depending on the design of the incubator and the way it is attached to the remaining limb, and these types differ in comfort level, weight distribution, stability during movement, and the most popular types used:
- Soft Insert Socket: This socket is commonly used in temporary prostheses or in patients in the early stages of amputation. It consists of a flexible sponge material placed inside a rigid exoskeleton, which provides greater comfort and pressure absorption on the sensitive areas of the limb, a belt or corset may be used to fix it to the leg and is a suitable option when the residual limb has not yet stabilized into a specific shape, or if there is skin sensitivity.
- Silicone Liner Socket: This type uses a flexible inner shell made of silicone gel to provide additional comfort and isolate the skin from direct pressure from the socket. This liner helps reduce irritation and friction and provides better stability when used with fastening systems such as pin-lock. This incubator is popular in everyday use and is suitable for a wide range of users, especially those with moderate activity.
- Vacuum-Assisted Silicone Suspension: This is one of the most advanced systems, using a silicone liner with a vacuum system that creates a pressure difference between the liner and the residual limb. This results in very high stability and minimizes movement of the limb within the liner, helping to improve balance, increase ground sensation, and reduce skin irritation. This type is preferred for active users or those who have sensitive skin and need additional stabilization.
How to choose the right prosthesis
The proper selection of a below-knee prosthesis is a critical step that affects comfort, function, and quality of daily life. This choice depends on multiple factors, most notably the shape of the remaining limb, the condition of the skin and tissues, and the patient’s activity level and movement goals. The prosthetist plays a key role in this process by taking accurate measurements and designing a suitable sleeve that ensures good fixation of the limb and balanced pressure distribution, as an inappropriate sleeve may cause irritation or chronic pain and hinder the use of the below-knee prosthesis.
Other selection factors include: the type of suspension (such as locking or suction), the balance of the below-knee prosthesis with the body, as well as the general health of the patient. Some patients with chronic diseases or weakness in the opposite limb may not be ideal candidates for the prosthesis, which requires a joint discussion with the doctor. In general, a preparatory below-knee prosthesis is started during the rehabilitation period, followed by a permanent one after the remaining limb is stable. The more appropriate and comfortable the design, the more opportunities for the patient to move with confidence, and the fewer complications associated with use.
Carbon prosthesis: Advantages and disadvantages
Carbon Fiber Prosthetics is one of the most prominent innovations in the field of prosthetics, due to its strength and durability compared to its lightweight. Carbon fiber is widely used in advanced industries such as aerospace and military industries, and has also proven its worth in designing limbs needed by active users and athletes.
Advantages
- Lightweight with very high strength: Reduces effort when walking and improves balance.
- Design flexibility: The material can be molded to the anatomy of the residual limb, providing a more natural movement.
- Resistant to corrosion and stress: Not easily affected by moisture or thermal expansion, and withstands repeated use.
- More comfortable for the user: No sharp friction against the skin and easy adaptation to the limb.
- Contemporary aesthetics: It comes in modern designs and colors that satisfy the preferences of all users.
Disadvantages
- High cost: Carbon limbs are more expensive than traditional limbs because of the materials and techniques used.
- Fragility under extreme pressure: Despite its strength, carbon fiber can be brittle to direct impact or sharp pressure, compared to titanium used in traditional limbs.
- Not suitable for all users: Some patients may require softer or more shock-absorbing materials for medical reasons.
How does the skin and bone condition affect limb selection?
The condition of the skin and bones of the remaining limb plays a key role in determining the type of below-knee prosthesis that is most suitable for each patient. Not all incubators or suspension systems are suitable for all cases, and the decision depends on a careful evaluation of the medical and physical condition of the limb, and the most important factors that are taken into consideration are:
- Skin condition: Skin that is weakened, sensitive, or suffering from chronic sores or infections may not withstand the pressure of a traditional incubator; in these cases, it is preferable to use a flexible liner such as silicone gel or suspension systems that do not rely on direct friction, such as a pneumatic suction system.
- The amount of soft tissue: If there is not enough tissue to cover the protruding bones, the patient may need a specialized design of the incubator to evenly distribute pressure and avoid ulceration.
- Joint flexibility and range of motion: Ensure that the remaining joint is sufficiently mobile, especially in cases where there is stiffness or restriction of movement in the knee or ankle, in which case the design may require modification to reduce pressure or improve balance while walking.
- Medical reason for amputation: Those who have lost a limb due to a chronic disease (such as diabetes or peripheral arterial disease) sometimes have less tissue quality than those who lost it due to an injury or accident, and this affects how well the skin and bone can withstand pressure and therefore the type of limb that is suitable.
Benefits of using a prosthesis in rehabilitation
Below-knee prosthesis plays a pivotal role in rehabilitation and regaining independence after amputation, as it is not only a means of replacing the lost limb but also a functional tool that improves balance, relieves pressure on the healthy side, and restores the ability to walk and move. The use of a below-knee prosthesis enables patients to gradually engage in motor exercises and strengthen their leg, arm, and trunk muscles, which is essential for overall physical balance. It also facilitates the practice of daily activities such as climbing, sitting, and walking on uneven surfaces, boosting self-confidence and accelerating the return to a normal lifestyle.
Another important benefit is that the below-knee prosthesis minimizes complications resulting from immobility, such as muscle weakness, balance disorder, or pain caused by overloading the other leg. Over time, and with regular follow-up with the rehabilitation team, many patients are able to return to the sports or occupational activities they practiced before the amputation.
Patient rehabilitation steps before and after fitting below-the-knee prostheses
The rehabilitation phase is an essential part of the successful use of the below-knee prosthesis and is as important as the design of the prosthesis itself. The rehabilitation process goes through several stages, starting before the prosthesis is fitted and continuing until full adaptation.
Before fitting, the medical team focuses on preparing the residual limb in terms of strengthening the muscles, reducing swelling, and maintaining the range of motion of the joint. At this stage, the patient is trained in skin care and the use of appropriate socks or compresses, and early communication begins with the prosthetist to determine the type of below-knee prosthesis.
After the initial fitting of the limb, gait training using the below-knee prosthesis begins, which is known as mobility rehabilitation. This includes working with physical therapists to strengthen the legs and arms, improve balance, and increase cardio-respiratory fitness. Below-knee prosthesis is more amenable to rehabilitation than above-the-knee limbs because preserving the knee joint greatly facilitates movement.
Over time, the below-knee prosthesis is adjusted according to the changing shape of the remaining limb, and periodic reviews are conducted to adjust the prosthesis in terms of balance and positioning, with the aim of improving the way of walking and reducing unbalanced pressure on the body. It should be noted that these steps are applied within a comprehensive plan that includes all types of lower limb prostheses, but they focus specifically on the needs of below-knee prosthesis users because of their greater adaptability.
Challenges and potential complications after prosthetic fitting
Despite the significant benefits of below-knee prosthesis in restoring mobility, the post-fitting phase is not without some challenges that affect the comfort or functionality of the patient, and these challenges vary from person to person and may be physical, functional, or psychological. Pain in the residual limb, known as Phantom Limb Pain, as well as skin issues caused by sweating or friction inside the incubator, and the change in the shape of the limb over time or muscle weakness may lead to poor stability or difficulty walking.
On a functional level, walking with below-knee prostheses requires more effort and may be accompanied by imbalance or movement pattern disorders, especially in the early stages of acclimatization. Psychological challenges are equally important, as some patients may have difficulty adapting to the physical change or feel isolated or socially awkward, especially if they do not receive proper support.
Understanding these challenges early and addressing them effectively in collaboration with the rehabilitation team is the key to maximizing the benefits of the below-knee prosthesis and avoiding long-term complications.
Dealing with pain or adjustment issues after installation
Patients with below-the-knee amputation may face pain or difficulties in adapting to the prosthesis, especially in the first stage, and the most prominent of these challenges is ghost limb pain, which can be alleviated with appropriate medications, or through non-pharmacological techniques such as mirror therapy and nerve stimulation exercises, and skin issues may appear as a result of excessive sweating or friction inside the incubator, and here it is recommended to take daily skin care and use soothing creams or change the liner when needed.
It is important to know that walking with a below-knee amputation prosthesis takes more energy, which can lead to rapid fatigue, so continuous follow-up with the rehabilitation team is recommended to adjust the limb and provide the necessary support to ensure proper adaptation and minimize complications.
Types of prosthetic pain
Many users of the below-knee prosthesis experience different types of pain during the acclimatization and use phases, some of which are normal and temporary while others indicate a defect in the design or use. It is important to understand these types to distinguish between what can be considered part of the adaptation process and what requires urgent technical review, and this table shows the types with their causes and ways to deal with them:
| Type of pain | Probable cause | How to deal |
| Friction pain | Skin rubbing against the liner or incubator due to sweating or prolonged use without ventilation or cleaning | Medications, mirror therapy, and neurostimulation |
| The pain of misloading | Poor weight distribution within the prosthesis due to misalignment or design error | Alignment Reset and Incubator Adjustment |
| Pressure pain | Prominent bony areas without adequate coverage | Designing a special incubator that distributes pressure and using additional liners |
| Phantom pain | Nerve signals from the brain feel pain in the missing limb | Muscle strengthening exercises, effort distribution, and proper rest |
| Muscle fatigue pain | Extra strain on the remaining muscles as a result of replacing the lost limb | Muscle strengthening exercises, effort distribution and proper rest |
| Pain caused by a faulty incubator design | Excessive or unbalanced pressure due to a malfunction in the suction system or the incubator itself | Technical review of the incubator and resetting the suction system |
The most important guidelines after amputation are to avoid complications or conditions that may affect the use of the limb
To achieve the best results when using below-the-knee amputation prosthetics, it is important to adhere to certain exercises and daily guidelines:
- Stretching exercises: Help prevent stiffness in the joints, especially the knee joint, and keep the remaining limb straight.
- Maintain range of motion: Simple joint flexion and extension exercises keep the joints supple, making it easier to use the prosthesis later.
- Strengthening muscles: After amputation, muscles become weaker due to lack of use, so strengthening exercises are essential to support the prosthesis and improve balance.
In conclusion, the below-knee prosthesis is an effective solution to regain mobility and independence after limb loss, but it requires a thorough understanding of the types of lower prostheses, their components, and the selection mechanism. Adherence to daily guidelines and rehabilitation exercises plays a pivotal role in achieving the best functional performance and avoiding complications. By knowing the difference between types of lower prostheses and dealing early with any pain or functional challenge, the patient can better adapt to the below-knee prosthesis and regain quality of life with confidence and safety.
Sources:
- Beshyah, S. A., & Nicolaides, A. N. (2019). Lower Limb Amputation. In StatPearls. StatPearls Publishing.
- Ottobock. (n.d.). Prosthetic legs. Ottobock Global.
