Overview of Transradial Prosthetics

Original Editor - Jess Bell based on the course by Donna Fisher
Top Contributors - Jess Bell and Ewa Jaraczewska

Introduction

Upper limb amputation is a life-changing event that has a profound impact on a person’s function, work, daily and recreational activities. Prosthesis use can have a positive impact on outcomes, helping to facilitate participation in various activities. However, despite technological advances, a number of people with transradial amputation reject their prosthesis. Appropriate prosthesis selection, fitting and training are essential to maximise engagement. Patients must also be actively involved in decision-making throughout the process.

This article introduces specific considerations for transradial amputation, providing an overview of the epidemiology, types of prostheses, and key measurement and fitting requirements.

Amputation is the surgical removal of all or part of a limb.

Traumatic amputation is an accidental injury that results in the loss of a limb or other body appendage.

Transradial amputation is an amputation between the elbow and wrist. It can be categorised as long, mid-length, short and ultra-short.

Epidemiology

It’s difficult to determine exactly how many people have had a major amputation globally, because many countries do not keep detailed records of people living with amputation. However, statistics are available for the United States (US). These figures show that around 2,309,000 people in the US are living with limb loss, 91% of whom have lower limb amputations, while only 9.2% have upper limb amputations. While there are differences between countries, these statistics provide a general picture of amputation patterns.

Common Causes of Amputation

The major causes of amputation are trauma (including conflict-related injuries, road traffic accidents and workplace accidents), diseases (e.g., cancer/malignancies and vascular conditions), and congenital limb differences.

Trauma is the primary cause of upper limb loss in adults, affecting 3.8 people per 100,000. The second most common cause of upper limb amputation is cancer. While vascular disease is a common cause of lower limb amputations, it does not often affect the upper limbs. The incidence of congenital limb difference also varies. Ramamurthy notes that it occurs in around 4-6 per 10,000 live births per year. Upper limb difference is 2-3 times more common than lower limb difference.

Key Demographic Features

Traumatic amputations tend to occur in younger, working populations. Most upper limb amputations are in people aged 20-40 years. Men are more likely to undergo trauma-related amputations and have a higher overall incidence of upper limb amputation. There are unique patterns in upper limb amputations across different countries and regions. In military populations, upper limb amputations are more common than in the general population.

Patient Types

This article focuses on three types of amputation/limb loss: traumatic, tumour-related and congenital limb absence.

Traumatic Transradial Amputation

People experiencing a traumatic upper limb amputation may have also experienced other injuries (poly-trauma). There may be complexities associated with their residual limb, in terms of length and shape. They may also having scarring and burns.

These injuries can have a profound psychological impact, and are associated with depression, post traumatic stress disorder (PTSD), psychological distress, decreased social interactions, etc. If you would like to learn more about these conditions, please see: Psychological Support in Rehabilitation.

Traumatic upper limb amputation can also lead to ongoing pain and phantom sensations. If you would like to read more about Phantom Limb Pain, please see Clinical Features and Mechanisms of Phantom Limb Pain and Phantom Limb Pain Rehabilitation Management.

Traumatic transradial amputation has a sudden and significant impact on function, with many people unable to return to their previous employment. Shahsavari et al. note that around half of all individuals with amputation face barriers in the workplace, and that people with upper limb amputations commonly need workplace adaptations, have difficulty returning to work, or need to leave their work. These individuals tend to require robust and reliable prosthetic solutions, but can become proficient users of more complex devices.

Tumour

Amputations to remove tumours are usually elective, or planned, life-saving or life-prolonging procedures. Because they are elective, surgeons may have more control over the length of the remaining limb. While there is often a preoperative period to prepare physiologically and psychologically for these amputations, they still have significant psychological impacts on people and can affect their body image. Many of these patients may be having other treatments, which can further impact their confidence. Like traumatic amputations, pain and phantom sensations can occur, and function is significantly impacted. These patients' goals often relate to body image and cosmesis. Prostheses and rehabilitation aim to optimise participation in daily life, hobbies and activities important to the person. However, many patients will not regain their prior ability to complete all these activities, which is an important psychological consideration.

Congenital Limb Absence

Children with congenital limb absence generally adapt well, but early intervention ensures the best outcomes. Goals and expectations change as a child grows, but goals for this population tend to be more function-based. Children may also want specific prosthetic adaptations to allow them to participate in certain activities (e.g., bicycle attachments, sports adaptations, musical instrument adaptations). These individuals often have a short residual limb, but tend to have a high level of function with or without a prosthesis.

Types of Transradial Prostheses

Upper limb prostheses can be categorised as passive or active depending on their function.

Passive/Cosmetic Prostheses

Despite their name, these prostheses are not entirely passive. They return a person’s limb length and assist in function (e.g., helping with bimanual tasks, like holding down paper when writing, stabilising objects, and helping to carry items). They have no moving parts, are low maintenance and tend to be lighter weight. They may be preferred by people who can't or don’t want to use other types of prostheses (e.g., children or older people). Rejection of prostheses is high in people with upper limb amputations (over 50% in some studies), so it's essential that these prostheses look good and are as light and comfortable as possible.

Componentry of Passive/Cosmetic Prostheses

The hands/terminal device of passive/cosmetic prostheses tend to be made from foam. Many have wired fingers for positioning. The wrist units can be plastic or wooden, and are round or oval. Gloves are primarily for cosmesis. They can be made of PVC, silicone or HD silicone. HD silicone gloves are the best option for cosmesis, but they are expensive and not available everywhere.

Body-Powered/Mechanical Control Prostheses

These prostheses are activated by the person’s remaining body, through the “transmission of muscle power to artificial joints”. A harness cable system is used to power distal movements. There are various options for terminal devices (TD), such as a simple pincer grip, hook or hand.

Componentry of Body-Powered/Mechanical Control Prostheses

The hands/terminal devices can have voluntary opening and closing (pincer grip). Other options include a split hook or task-specific terminal devices, such as tool holders, sports adaptations or requested customisations. The wrist units are quick-release and interchangeable. They have passive rotation and flexion/extension. The harness system uses body movements to stretch and release a cable to open or close the terminal device.

This video shows different options for body-powered terminal devices:

Body-powered devices are not a cosmetic option and are designed for manual work or heavy-duty use. The harness can be uncomfortable and they require training and maintenance. The user must have sufficient strength and range of motion to pull the harness cable to make the device work.

The following video demonstrates rehabilitation therapy protocols for transradial body-powered prostheses, from assessment to therapy and a final quality check:

Myoelectric Control Prostheses

Myoelectric control prostheses require a functional level of muscle signal, preferably from two sites, but it is possible to just use one. Electrodes pick up electromyographic (EMG) signals and magnify this response. The control unit allows for different movements in the hand and wrist.

The following video demonstrates how myoelectric control prostheses work:

The terminal devices include hands, electric hooks, and wrist rotation units. There are options for silicone, PVC or HD gloves. They require daily charging and ongoing training and maintenance. They can also be more expensive.

Componentry of Myoelectric Control Prostheses

The electric hands/terminal devices have multiple functions and movements. Independent thumb and finger movements are possible. The electric wrist units allow control and movement of rotation and can allow flexion and extension passively. The control system magnifies the signal and sends it to the terminal device to power the programmed movement.

Socket Design and Suspension

Traditionally, sockets have been manufactured from a cast using a lamination technique, with a two-part resin system. Test sockets are generally draped from thermoplastic for ease of adjustment. They have a flexible inner socket with a carbon fibre outer shell, which provides the attachment point for the wrist and hand.

Socket materials may be influenced by the suspension method. Suspension options for transradial amputations include supra-olecranon, suction/vacuum, pin lock and harness suspension.

The supra-olecranon system uses the natural bony anatomy to suspend the prosthetic above the olecranon. This system is not always comfortable and it can limit elbow movement. It generally requires a prosthetic sock, which is not ideal for myoelectric prostheses as it interferes with electrode contact.

In a suction/vacuum suspension system, the residual limb is pulled into the socket, and the air is expelled. A valve can be used to seal the vacuum system. This approach can be combined with supra-olecranon/supracondylar suspension. While donning and doffing can be difficult, it is suitable for all prosthetic types.

In the pin lock suspension system, a liner is rolled onto the residual limb, which is connected to the socket by a pin or lanyard. It is a secure connection that is easy to release. This system may not be suitable for myoelectric fittings as the liner blocks the myoelectric signals. It can be difficult to manage the liner, and there can be issues with sweating.

The harness system isn't used as frequently. It is a traditional system that uses straps. It is usually attached to the socket and then looped around the olecranon and condyles. There can be friction and skin issues, but it is a useful system in situations where additional security is required (e.g., during heavy work or gym training).

Measurement, Casting and Fitting Procedures

There are various techniques for shape and volume casting, including plaster casts, scanning and modification.

"Plaster casting and manual rectification represent the benchmark prosthetic socket design method. 3D technologies have increasing potential for prosthetic limb design and fabrication, especially for enhancing access to these services in low-resource settings."

Key measurements include:

• hand size: diameter of the metacarpals, circumference, finger length of the remaining limb
• olecranon to thumb tip distance of the remaining limb
• residual limb length

The following videos demonstrate the casting and fabrication process for a body-powered prosthesis. The first video shows how to make a plaster cast negative from a person with a transradial amputation. The second video shows how prosthetists fabricate a test socket:

Test Socket Fitting

Test socket fitting is essential for identifying and addressing potential issues before fabricating the prosthesis. Prosthetists check the volume, length, and hand size, the suspension, ease of donning and doffing, and comfort, paying attention to areas of reduced sensation. They also check elbow flexion, general freedom of movement and length (thumb tip to thumb tip, reaching, inside clothing).

Definitive Socket Fitting

This is the final opportunity to ensure comfort and function before use. Prosthetists will check comfort, donning and doffing, suspension, length, freedom of movement, and cosmetic finish.

Body-Powered Control/Mechanical Fitting Procedures

Body-powered systems require additional fitting considerations due to the harness and cable system.

During the test socket fitting, the prosthetist checks the harness fitting, fixing position and function of the cable and terminal device.

Then, during the definitive socket fitting, there is a final fit of the harness and cable, fixing of the cable and function of the terminal device. It’s important to check for any impedance from the cosmetic glove.

The following optional video will give you an idea of the fitting process for a body-powered harness for people with a transradial amputation:

Myoelectric Fitting Procedures

Myoelectric systems require specialised fitting procedures to optimise EMG signal detection and control. An initial muscle signal assessment must be performed. This assessment tests the strength, consistency and co-contraction of muscle signals. This assessment also allows the clinician to establish the optimal position of the electrodes. These positions are marked on the cast.

The following video demonstrates one method for evaluating myosignals:

During the test socket fitting, the prosthetist checks the electrode position and muscle signal to the terminal device, actions in different positions and co-contraction for wrist movement. In addition, the sensitivity of the electrodes must be adjusted.

These devices require specific training with a rehabilitation professional (e.g., a physiotherapist or occupational therapist).

During the definitive socket fitting, the prosthetist will again check the electrode position, muscle signal to the terminal device, actions in different positions and co-contraction for wrist movements, and they will adjust the sensitivity of the electrodes.

Summary

A transradial amputation profoundly impacts a person's function. It is essential to find an optimal prosthetic solution for people with upper limb amputation to ensure active participation in daily, work and leisure activities.