Merck Manual

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Prosthesis Fitting


Jan J. Stokosa

, CP, American Prosthetics Institute, Ltd

Reviewed/Revised Mar 2024

A prosthesis has 7 basic parts:

  • Residual-limb gel cushion interface: A silicone gel or viscoelastic material that protects the skin and adjusts pressure

  • Suspension system: Connects the prosthesis to the body

  • Socket: Rigid plastic receptacle into which the residual limb with gel interface is inserted (there may be an inner primary flexible socket that helps adjust pressure)

  • Joints (ankle, knee, wrist, elbow) and terminal appendage (hand, foot)

  • Modular endoskeletal system connection couplings: Connect prosthetic joints and terminal appendages and provide adjustability

  • Anatomic shape: Soft foam material that simulates muscle contours and protects endoskeletal components

  • Synthetic skin: Thin, tone-matching layer applied over the anatomic shape

During the fitting process, the prosthetist makes a mold of the residual limb using plaster or fiberglass bandages or by digital imaging. The mold or digital image is used to create a positive model of the limb, which is then modified to better match the individual characteristics of the person's residual limb.

A socket is formed around the model. This socket is integrated into a diagnostic prosthesis to test various component combinations and determine which option provides the most comfort, stability, function, and efficiency. Because the fit of the prosthetic socket is so important, prosthetists may require several tries to achieve optimal socket comfort and stability.

Once the socket fit is finalized and the components and design have been determined, the definitive socket is fabricated, usually of carbon fiber and other durable materials, and the definitive prosthesis is aligned and optimized. The external appearance is created, either an anatomically realistic one or one that leaves the components exposed. The fitting process takes 7 to 18 visits, depending on complexity, and approximately 16 laboratory fabrication procedures.

Transcutaneous osseointegration

Transcutaneous osseointegration, an alternative to a traditional socket prosthesis, involves surgically implanting a prosthetic anchor into the residual limb’s bone, modifying the soft tissue connection from the residual limb to the prosthetic socket. This alternative may be especially helpful for people who previously had a poor experience (including pain, lack of stability, and skin problems) with their socket prosthesis.

Various prosthetic appendages can be attached directly to the implant. An opening in the skin at the end of the residual limb allows the implant to extend out of the limb and attach to component elements (such as joints and appendages).

Complications from transcutaneous osseointegration are uncommon but include infection and fracture of the bone in the residual limb, as well as loosening of the implant after integration. To minimize potential harm, a mechanism is inserted between the implant and the prosthesis that automatically releases during a severe fall. This protects the implant and reduces the possibility of bone fracture.

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