Prosthesis

Prostheses are medical devices designed to replace missing body parts, restoring function, appearance, or both. They may be required following traumatic injury, disease, or congenital absence. Modern prosthetics combine medicine, engineering, material science, and rehabilitation to support individuals in regaining mobility, independence, and quality of life. The development and fitting of prosthetic limbs involve a highly skilled interdisciplinary team and increasingly sophisticated technologies.

Definition and Medical Application

A prosthesis is an artificial replacement for a missing body part. Such devices range from simple cosmetic substitutes to highly functional mechanical or electronic systems capable of complex movements. The loss of a limb may be due to conditions such as trauma, vascular disease, or congenital anomalies. Rehabilitation is typically coordinated by professionals in physical medicine and involves prosthetists, physiotherapists, occupational therapists, and nursing staff.
Prostheses may be produced manually or with computer-aided design (CAD) systems, which enable accurate modelling, analysis, and optimisation. CAD techniques allow practitioners to design components with precise anatomical fit and improved functionality.

Categories of Prosthetic Devices

A prosthesis must be tailored to meet an individual’s functional requirements, aesthetic preferences, available resources, and personal goals. Factors influencing choice include comorbidities, lifestyle, occupational demands, and access to health care.

Craniofacial and Intraoral Prostheses

Craniofacial prostheses address structural loss of the face and head. Extraoral types include:

• Hemifacial and auricular (ear) prostheses
• Nasal prostheses
• Orbital and ocular devices

Intraoral prostheses encompass dental replacements such as dentures, palatal obturators, and implants. Neck prostheses include replacements for the larynx, electrolarynx devices, and various tracheal and upper oesophageal supports.

Torso Prostheses

Torso-related prostheses include breast prostheses, provided singly or bilaterally, as well as nipple prostheses. Penile implants may be used therapeutically for erectile dysfunction or for reconstructive procedures, including phalloplasty or gender-affirming surgery.

Limb Prosthetics

Limb prostheses are among the most widely used categories and are divided into upper-extremity and lower-extremity devices.

Upper-Extremity Prostheses

Upper limb prostheses are used at multiple levels of amputation, including shoulder disarticulation, transhumeral and transradial levels, wrist disarticulation, and partial hand or finger replacements. A transradial prosthesis replaces the arm below the elbow.
These devices may be grouped into three primary types:

• Passive devices, which may be static or adjustable. They are typically cosmetic or serve to support objects during bimanual tasks or social interaction.
• Body-powered devices, which use harness and cable systems connected to body movements. Variants have recently explored respiratory-based control mechanisms.
• Myoelectric devices, which incorporate batteries and motors. These detect muscle signals via techniques such as electromyography, sonomyography, or myokinetic sensing. Electrical signals generated by muscle contractions are interpreted as commands for the artificial hand.

Within clinical practice, a transradial prosthesis is often referred to as a BE (below elbow) prosthesis.

Lower-Extremity Prostheses

Lower limb prostheses accommodate various levels of amputation, including hip disarticulation, transfemoral, knee disarticulation, transtibial, and partial foot replacements. A transtibial prosthesis replaces a leg below the knee, while a transfemoral prosthesis replaces one above the knee.
Transfemoral amputees experience significantly higher energy expenditure during walking owing to the mechanical complexities of knee function. Modern designs integrate hydraulics, carbon fibre, microprocessors, and motorised systems to improve stability, gait symmetry, and user control.
Transtibial amputees generally regain movement more readily because the natural knee is preserved. In clinical terminology, transfemoral and transtibial devices are referred to as AK (above knee) and BK (below knee) prostheses respectively.

Clinical Practice and Rehabilitation

Prostheses are designed, fitted, and adjusted by clinical prosthetists, who specialise in alignment, gait evaluation, and long-term device management. Following fitting, rehabilitation physiotherapists support users in learning to walk or perform upper-limb tasks with their prostheses. Training may take place in clinics or home environments.
Emerging evidence suggests that treadmill-based home programmes may enhance adaptation by allowing repeated exposure to gait challenges. However, for individuals with dysvascular conditions—responsible for approximately three-quarters of lower limb amputations in the United Kingdom—recovery can be complicated by comorbidities such as diabetes and cardiovascular disease. Research remains limited regarding optimal rehabilitation strategies for this group.

Amputation Levels and Classification

Lower extremity prostheses are often categorised according to amputation level or associated surgical techniques. Common categories include:

• Transfemoral and transtibial
• Symes (ankle disarticulation)
• Knee and hip disarticulation
• Hemipelvectomy
• Partial foot amputations such as Chopart, Lisfranc, and transmetatarsal levels
• Ray and toe amputations
• Van Nes rotationplasty, a specialised reconstructive technique

Materials and Manufacturing

Modern prosthetics make use of lightweight, durable materials to enhance user comfort and mobility. Common raw materials include:

• Plastics such as polyethylene, polypropylene, acrylics, and polyurethane
• Metals including aluminium
• Composites, particularly carbon-fibre reinforced polymers
• Earlier materials such as wood and rubber are now largely historical but were foundational in early prosthetic design.

Prostheses are increasingly fabricated using CAD-based workflows, additive manufacturing, and advanced composite layering to optimise strength-to-weight ratios.
Wheeled prosthetic devices are also used in veterinary rehabilitation, supporting mobility in animals such as dogs, cats, and turtles.

Organ Prostheses

Beyond limbs, prosthetic technology includes organ prostheses such as artificial hearts and kidneys. These devices replicate vital physiological functions and represent a distinct but related field within biomedical engineering.

Historical Development

The origins of prosthetics date back to the ancient Near East around 3000 BCE. Archaeological evidence from ancient Egypt and other early civilisations shows sophisticated attempts to replace missing body parts, demonstrating the longstanding human endeavour to restore physical capability and bodily integrity through artificial means.