A prosthetic is defined as an artificial implant that replaces a missing part in the body that was lost through trauma, congenital disorders, or severe diseases like cancer to provide an opportunity to perform functional tasks. Any prosthetic device can be constructed using the following components.

  • Socket
  • Body
  • Harness/Suspension
  • Control system
  • Terminal device

Socket

The socket fits with that of the stump (end of the amputated region). In the case of an arm prosthesis, the socket is made of resin double wall with lightweight plastic where the inner wall attaches to the stump and the outer attaches to the contour of the forearm.

Harness

It is attached to the socket to provide support, stability, attachment to control cables, and help in the control of the device.

Terminal device

It is attached to the socket of the forearm by the wrist unit, to help in passive pronation and supination. There are two types, passive and active. Passive is used for a cosmetic appearance like baby mitts for crawling and ball handling devices to play ball-related sports. Active devices use hooks with prehensors for thumb and finger components or use artificial hands.

Power control system

Based on the force and power, there are two types, namely body-powered and externally powered systems. Body powered uses the force from the body for movements that are transmitted to the device through the cables. Forward flexion and relaxation of the shoulder provide force for a device for open and close positions respectively. The forces are transmitted through the Bowden cable. Some examples are bicapsular protraction; abduction, internal rotation, and shoulder extension to lock the elbow.

Externally powered systems use either switches or electric control. The switches are present inside the socket or in the harness system that can be operated by cable or electric power. The cable-operated system consists of a voluntary opening and closing mechanism. The patient uses the cable to control motion and grasp objects, which works against the resistive forces of internal springs and rubber bands. Contraction of muscles results in opening and relaxation results in closing.

The electric control is called as Myoelectric due to the electric signals produced by the neuromuscular system in the existing part of the residual limb. It consists of electrodes, a battery, an electric hand, and a friction wrist in addition to the standard components. Sensors relay information to the controller which controls the hand. The future of myoelectric prosthesis is the intelligent hand and 3D printed models.

Upper limb prosthesis

These prostheses replace the upper limb including the wrist, upper hand, and shoulder. There are four types namely passive, body-powered, externally powered, and hybrid. The passive system acts as a stabilizer and is cosmetics, used for patients who don’t have enough strength to control the prosthesis. The body-powered system uses power from the residual limb of the patient, external power uses electricity to control and the hybrid is the combination of both where the terminal joint is externally powered and the elbow is body-powered.

Lower limb prosthesis

Based on the usage, there are two types, permanent (definitive) and temporary (preparatory). The socket is custom-made and attached to a cast of the patient’s residual limb in order to maintain contact. Pressure tolerant and sensitive regions receive higher and lower pressure respectively and can reduce edema, and increase proprioception and weight distribution. The cast is made using plaster of pairs or high-density polyethylene (HDPE) at 200 celsius.

The suspension is a pelvic belt or supracondylar calf that is attached to the residual limb. There are two types of connections namely exoskeletal and endoskeletal.

Exoskeletal

A laminated shell made of resin or HDPE, filled with wood or foam, provides a cosmetic appearance and supportive strength.

Endoskeletal

Connectivity by pylons, made of carbon fiber or steel for the angular and linear change in coronal and sagittal planes for height adjustment.

The lower limb prosthesis absorbs shock, provides stability for gait, simulates muscle activity in the swing and stance phase of gait, and performs plantar flexion and dorsiflexion, inversion and
eversion.

Solid Ankle Cushion Heel

The SACH is a lower limb prosthetic designed by Foort and Radcliffe in 1956. It is an endoskeletal pylon ankle adaptor to restrict all kinds of motion during gait and has to be used with shoes because the toes are discernable.

Jaipur feet

Developed by P K Sethi and the team from SMS medical college, the prosthetic provides enough dorsiflexion to permit amputee to squat, transverse rotation of the foot on the leg to facilitate walking and cross-legged sitting, and sufficient range of inversion & eversion to allow the foot to adapt itself while walking on the uneven surface due to elasticity of rubber material

A knee prosthesis provides adequate stability in the stance phase and gets aligned with the knee during the extension phase. If the knee mechanism does not fully extend before heel contact it buckles causing the prosthetic knee to flex suddenly when weight is applied.

Know about rehabilitation

Know about time and light