Prosthetics for Lower Limb Amputation

All types of prosthesis are well explained with their application and advantages. Each prosthesis has its own uniqueness and the patient will be well rehabilitated with those prosthesis. Not all the patients are permitted into rehabilitation stage. It depends on factors like age, built of the patient, involvement of the limb (bilateral or unilateral), Psychology of the patient, socio-economical status of the patient. A multi- specialist Rehabilitation team has to be set to rehabilitate the Amputee.

11.1 Biomechanical principles of prosthesis and gait in prosthetic leg

The gait cycle which consists of two stages will also be termed as walking cycle. Initial contact is the first step in the starting point and the end point in every gait cycle. A single gait cycle has two phases. The stance phase and the swing phase. The stance phase is the initial step in which the foot contact starts followed by other steps in the ground. The stance phases contribute about 60% of the gait cycle and the swing phase contributes about 40% of the gait cycle. The swing denotes the single leg support in which the foot is off the ground.

The pattern of gait in subjects with prosthesis will present an altered gait pattern. Here the foot contact on the ground and the weight distribution on the foot is the key factor to be noted. The foot contact will occur on the heel in such a way the walking cycle will be as natural as possible. In this situation the sole of the foot will contact the ground and the weight is transmitted to the foot. Thus, the selection of foot component and the knee joint must be proper. This is because this will have an influence on the subject’s gait when he turns on to the next phase [9].

During swing phase, the knee function is so important so that the mobility on the knee joint performing both flexion and extension facilitating the foot transition from plantar flexion to dorsiflexion i.e toe elevation. This will prevent the subject from stumbling and subsequent fall.

The residual limb must be placed on the socket which provides rigid and stable attachment to the limb. This aids control over the subject’s limb during walking. The prosthesis socket can be divided into 3 parts. The top region of the socket is known as seating face. The central part of the socket is the primary control area. The function of the central part is to ensure correct movement and restrain it in the PA direction during walking. The last part is the distal socket end. This part will transfer only 10% of the subject weight to avoid abnormal weight transfer and this will cause subsequent damage to the soft tissues. The socket must be able to transfer the load thereby it ensures good stability of the subject’s gait with better control [10].

During standing, there will be a stretching of gluteus medius muscle. This will maintain the pelvis in a balanced position. For a subject with lower limb amputation this pelvis position is taken care by the prosthetic socket. In a transverse oval socket of transfemoral prosthesis, the pressure on the distal femur end increases and the body is excessively bending aside to reduce the pressure. It is a non-physiological load transfer, as the load is transferred through the tuberosity of the ischium which reduces the arm of the exerted force and the overturning moments are increased.

If there is any problem in procedure of construction and principles in aligning the prosthesis, there will be an abnormal deviation that may develop during gait. This gait deviations uses more energy expenditure during walking. Once this is practiced as a routine, may result in over use of certain muscle groups which also causes muscle imbalance.

In most cases, the improper construction of the transfemoral prosthesis and transtibial prosthesis includes

1. On circumduction, the foot swings outward which increases resistance to knee flexion with prosthesis. Here the prosthesis knee flexion has been limited for a reason. Thus, the subject has developed the avoidance mechanism.

2. The lateral flexion of the spine, the subject presents a leaning gait with the shoulder depressed towards the affected side. This is due to prosthetic foot is outset greater than 25mm, incorrect prosthesis length, insufficient adduction or amputee sensitivity.

3. Excessive heel raise, where the heel of the prosthetic foot comes up too far and too quickly. This is due to prosthetic knee flexion resistance is inadequate for the patient.

4. Drop off during the late stance, the subject presents excessive knee flexion. This is due to softness of the keel of the prosthetic foot. Also, the toe lever of the foot is too short of the heel height of the shoe is too high.

5. Foot slap, this occurs along with rapid and abnormal plantar flexion movement immediately after heel contact. This is due to insufficient resistance to plantar flexion on the prosthetic foot.

Thus, if there is an improper prosthetic fitting, there will be pain and altered muscle activity during execution of the normal daily activities. This pain may cause lateral asymmetry of the body which is due to incorrect length of the prosthesis or incorrect selection of the prosthetic component. This wrong construction can lead to abnormal force transmission, overloading the various muscles involved and also damage to the soft tissues which may affect the integration of the stump function.