Prosthetic legs replace a missing leg. The breakthrough in leg prosthetics was the integration of mechanical joints. Modern prostheses thus restore a variety of dynamic leg functions and give patients a better quality of life.
What is a prosthetic leg?
Innovations in leg prosthetics allow affected individuals to live more independent and active lives. They thus give patients a better quality of life. A prosthetic leg is used to restore a functional limb after amputations or in cases of deformity. The first leg prosthesis was made of wood and thus enabled ideal friction. This criterion is still considered one of the most important features of leg prostheses today. The first prostheses had only limited mobility. They served as supports, but not as active instruments of locomotion. After the First World War, the value of prosthetics increased due to the numerous war injuries. In arm prosthetics, the first active prostheses were developed at that time, whose joints could be moved without the aid of the healthy arm. In leg prosthetics, the first leg prostheses with knee joints were developed around the same time. The first bioelectronic knee joint was called the C-Leg. With this leg prosthesis, the Otto Bock company designed the first leg replacement that gave transfemoral amputees an improved walking pattern. The world’s first truly active leg prosthesis was invented at the turn of the millennium. This so-called Power Knee is an adaptive and electromechanically operated prosthesis model that measures the impulses of the healthy leg and transmits them to the motor of the prosthesis.
Shapes, types and styles
One main difference is in prosthetics between closed and open implants. Closed implants are joints that are entirely contained by healthy tissue. Open leg prostheses, on the other hand, are required when an entire limb is lost. Open implants are available as passive prostheses and, since the 2000s, as active prostheses. Depending on which parts of the leg are affected by an amputation or deformity, medicine distinguishes between transtibial prostheses, forefoot prostheses and transfemoral prostheses. Forefoot prostheses are given to patients with amputated toes, amputations up to the midfoot or of the entire foot. Transtibial prostheses, on the other hand, are intended for transtibial amputees. There are different systems for this type of prosthesis. The most common is the short prosthesis with a so-called adhesion system. The patient puts on a liner and climbs with the liner into a firmer prosthetic socket. Femoral prostheses involve amputation of the entire leg. This type of prosthesis requires complex systems to replace the knee joint. A variety of socket techniques and liners are available today for this purpose, allowing different leg constructions.
Structure and mode of operation
Leg prostheses are designed to take over loads during the stance phase and ensure a secure stance. Apart from this, they must be able to take over dynamic functions of the amputated or missing leg and also improve the patient’s gait pattern to create mobility that appears as natural as possible. To this end, leg prostheses are equipped with controllers in addition to a hydraulic system, which is intended to replace the control by the brain that has become impossible. When standing, for example, the leg must know that the wearer is standing in order to have a stabilizing effect and provide the wearer with stability. In the same way, however, it must recognize when the patient is walking and in which gait phase he or she is currently in. The C-Leg met these requirements as the first thinking leg prosthesis. This prosthesis continuously collects data via sensors to determine the gait phase. An angle sensor determines the flexion angle. A moment sensor with a tube adapter determines the load direction. The motor and hydraulic valve of the prosthesis are connected to the sensors and are activated and coordinated by the processing controller based on the data. Because the controller processes data collected in seconds, the swing phase and stance phase can be adjusted in relative real time, and the lower leg swing matches the stride speed during walking, for example. Other leg prostheses use a fluid system with a magnetorheological fluid mass instead of a hydraulic system together with the controller.The particles in the oil-like fluid change their viscosity in proportion to the strength of the magnetic field, depending on the sensor data. The active Power Knee goes even further in terms of dynamic prosthetic functions. These prosthetic legs contain special sensors on the sole of the foot that immediately detect the gait phase and adjust the power of the motor accordingly.
Medical and health benefits
Losing an arm is associated with fewer limitations than losing a leg. The healthy arm can partially compensate for the loss of the other and take over its functions to some extent. Such compensation is more difficult with legs. Therefore, the loss of one leg causes a great loss of mobility. Not only locomotion but also safe standing is impossible with one leg. Leg prostheses therefore have an enormous medical benefit. Active prostheses in particular, as they exist today, play an irreplaceable role in prosthetics. Locomotion is a complex process. A smooth course is ensured by innumerable interconnections of the nervous system and the motor pathways. The fact that this safeguard can nowadays be approximated by sensor-controller systems with a motor is due solely to the progress of the technological age. In the initial phase of leg prosthetics, wooden prostheses without joints were able to take over supporting functions, but the dynamic losses were still very high. The innovations in leg prosthetics enable patients to lead more independent and active lives. They thus give patients a better quality of life. The visually aesthetic effect of a leg prosthesis should also not be underestimated, which also relieves sufferers psychologically.
