Overview of Transhumeral Prosthetics

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

Introduction

Transhumeral amputation profoundly impacts a person’s independence and quality of life. Prosthesis use can facilitate continued participation in work, leisure and daily activities.

Transhumeral prostheses are complex devices that replace elbow, wrist and hand function. Prosthetic technology continues to evolve, particularly with advances in AI and 3D printing, offering increasingly sophisticated solutions. Despite these advances, understanding fundamental principles of suspension, socket design and fabrication remains essential.

This article focuses on prosthetics for transhumeral 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.

Transhumeral amputation is an amputation above the elbow and wrist. It can be categorised as short, mid-length and long.

Epidemiology

Comprehensive global statistics on people living with amputation are not readily available. However, more detailed data exists for the United States (US). In the US, approximately 2.3 million people live with limb loss—91% have lower limb amputations and 9.1% have upper limb amputations. Precise statistics on the proportion of transhumeral amputations among upper limb amputations are not readily available, but they make up a small percentage of upper limb amputations. Most upper limb amputations (around 78%) are finger amputations.

Common Causes of Amputation

The major causes of upper limb amputation are trauma (including conflict-related injuries, road traffic accidents and workplace accidents), diseases (e.g., cancer/malignancies and vascular conditions), and congenital limb absence/difference. Trauma accounts for 80% of cases. The second most common cause of upper limb amputation is cancer. Congenital limb absence occurs in around 4-6 per 10,000 live births per year.

Key Demographic Features

Traumatic amputations tend to occur in younger (20-40 years), working populations. Males have a higher overall incidence of upper limb amputation and are more likely to experience trauma-related amputations. Upper limb amputations are also more common in military populations than in the general population.

Types of Transhumeral Amputation

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

Traumatic Transhumeral Amputation

Traumatic upper limb amputations are often caused by workplace injuries involving heavy machinery, industrial accidents or electrical incidents. Other causes include road traffic accidents and conflict/combat. These injuries have a significant physical and psychological impact, and patients tend to have high expectations and functional goals. The residual limb is often complex in traumatic amputation, and there may be additional injuries. Injuries may be bilateral or impact the dominant hand, which has functional consequences. Other issues include scarring, pain and phantom sensations. Employment options for these individuals may be limited, and they tend to need a robust and reliable prosthetic solution. Individuals with traumatic transhumeral amputation often become proficient with complex prosthetic devices.

Tumour-Related Amputation

Because tumour-related amputations are elective (or planned) life-saving or life-prolonging surgeries, the length of the residual limb can often be optimised. While a patient may have time to prepare for these amputations, they still have a psychological impact, can affect body image, and cause pain and phantom sensations. These patients’ goals and expectations often focus on cosmetic appearance and body image. As with traumatic amputations, hand dominance is an important consideration.

Congenital Limb Absence

Children with congenital limb absence generally adapt very well and are highly functional without a prosthesis. Their goals and expectations change as they grow, but early intervention (i.e., from when a child is aged 3-5 months) enhances outcomes. Goals are often function-based and related to specific tasks (e.g., riding a bike, sports adaptations or playing musical instruments).

Prosthesis Rejection

The prosthetic rejection rate is high for people with all levels of upper limb amputation (around 45%). Key reasons for abandoning upper limb prostheses include comfort, weight, and function (e.g., control and sensory feedback).

Types of Transhumeral Prostheses

Upper limb prostheses can be categorised as passive or active. They are non-weight-bearing devices that replace hand, wrist and elbow function. They require individualised solutions/goals and intensive training.

Passive/Cosmetic Prostheses

Despite their name, these prostheses are not entirely passive or cosmetic. They restore the length of a person’s arm and can play a valuable role in body image. They can be static or have moving parts. While they are often lighter, weight can still be an issue.

Componentary of Passive/Cosmetic Prostheses

The hands/terminal devices of passive/cosmetic prostheses tend to be made of foam. Wrist units are round or oval and can be plastic or wooden. The elbow units can be endoskeletal (central inner skeletal structure), exoskeletal (hard outer shell), with a locking or fixed position. Gloves are important for cosmesis. They can be made of PVC, silicone or high-definition silicone.

Body-Powered Control/Mechanical Prostheses

These prostheses use a harness system to activate the hand and/or elbow units. Body movements are used to open and close the terminal device. There are various types of terminal devices and elbow units.

Componentary of Body Powered Control Prostheses

The hands/terminal devices have a voluntary opening and closing function (i.e., a pincer grip). Options for terminal devices include split hooks, various tool holders, sports adaptations and customised terminal devices. The wrist units are quick-release, and users can switch between different terminal devices. They allow passive rotation and flexion/extension. The elbow units can be controlled manually. They may have a spring assist, cable control or a locking mechanism. The harness system for body-powered devices is complex. It uses body movements to stretch and release a cable to activate the elbow and hand. It may also act as a suspension system.

Body-powered prostheses are not usually a cosmetic option. They are designed for manual work or heavy-duty use. The harness can be uncomfortable and effective use requires training and ongoing maintenance.

Myoelectric Control Prostheses

These prostheses are complex and can be heavy. They require a functional level of muscle signal, preferably from two muscle sites, but it is possible to use just one. They require intensive training, ongoing maintenance and they must be charged regularly. They are not designed for manual work or heavy-duty use.

Componentary of Myoelectric Control Prostheses

In this system, myoelectrodes are placed on the skin where they pick up EMG signals from muscles. The control system magnifies the signal and sends it to connected devices to power programmed movements.

This optional video demonstrates how muscle signals are evaluated:

Myoelectric control prostheses have electric hands/terminal devices, electric wrist units and electric elbow units. The terminal devices include hands, electric hooks and wrist rotation units. PVC, silicone and high-definition silicone gloves are used for cosmetic effect.

This video shows the different functions of an electric Greifer:

The electric wrist units allow control and rotation. They also allow for passive flexion and extension. The electric elbow units allow for flexion and extension control and passive rotation. This video demonstrates some of the features of the dynamic arm, a type of myoelectric prosthesis:

Myoelectric control prostheses are designed for light work and general use. They can incorporate both passive and electric control. They require training and ongoing maintenance. Socket design and fit are key to success but weight can be an issue. Therefore, secure suspension of the socket is also essential.

Advanced Myoelectrics

These advanced devices use pattern recognition and AI to enable complex movements. They are lighter and have more robust componentry, but cost and availability remain challenges.

This optional video introduces Myo Plus pattern recognition, which uses AI to control myoelectric terminal devices.

Socket Design and Suspension

Traditionally, sockets have been manufactured to a cast using a lamination technique with two-part resin. Test sockets are generally draped from thermoplastic for ease of adjustment. The inner sockets are flexible and surrounded by an outer carbon fibre shell, which provides the attachment point for various components.

The socket materials may be influenced by the suspension and type of prosthesis. Suspension options for transhumeral amputations include: suction/vacuum, pin lock and harness.

Suction/vacuum suspension: In this system, the residual limb is pulled into the socket, and air is expelled. A valve can be used to seal the vacuum system. This approach can be combined with over-the-shoulder suspension. Donning and doffing can be difficult, but it is a suitable suspension system for all prosthetic fitting types.

Pin lock suspension system: In this 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. However, it can be difficult for people with transhumeral amputations to manage the liner, and there can be issues with sweating. This system may not be suitable for myoelectric fittings as the liner blocks the myoelectric signals.

Harness suspension: This is a traditional system that uses straps. It can be custom-made, but there are off-the-shelf options available. The suspension sits over the shoulder and around the contralateral side. There can be skin and friction issues. It is also difficult to set up correctly and requires maintenance.

Measurement, Casting and Fitting Procedures

There are various methods to capture the shape and volume of a socket, including plaster casts, scanning and modification.

Key measurements include:

• hand size: diameter of the metacarpals, circumference, finger length
• olecranon to thumb tip
• axilla to elbow joint
• residual limb length

To learn more about casting for a transhumeral prosthesis, watch these optional videos:

After casting, a test socket fitting is completed. The prosthetist checks for volume, comfort and general fit. They must check the shoulder to elbow and elbow to hand lengths, and the overall length in sitting, standing, as well as hand size. They check the suspension (harness set-up, suction/vacuum or pin lock), as well as ease of donning and doffing, comfort and general freedom of movement.

Watch the following videos to see how a test socket of a body-powered transhumeral prosthesis is fabricated and how a flexible definitive inner socket is created.

The prosthetist then completes a definitive socket fitting. They again check for comfort. This is important as the materials may have changed since the test socket and there may have been a change in volume. They also check donning/doffing, the suspension, lengths, 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 the function of all the components.

During the definitive socket fitting, they complete a final fit of the harness and cable, fix the cable and perform a functional assessment. It’s important that they check for any impedance from the cosmetic glove.

Myoelectric Control Measurement and Casting Procedures

Myoelectric systems also require specialised procedures. The prosthetist tests muscle signals, looking at strength, consistency and co-contraction. They establish the optimum position of the electrodes and transfer this position to the cast.

This video demonstrates how myotomes can be tested using the myosmart cuff:

During the test socket fitting, the prosthetist assesses for socket fit, comfort and movement. They also check the electrode position and the muscle signal to the terminal device.

Next, they test and train the patient to activate the hand, terminal device and elbow, and adjust the electrode sensitivity. They also check for co-contractions. Patients being fitted with a myoelectric control prosthesis need to complete training with a physiotherapist/occupational therapist.

During the definitive socket fitting, the prosthetist again checks for fit, comfort, movement and lengths. They check the electrode positions, actions in different positions and co-contraction movements. They adjust the sensitivity of the electrodes and ensure the patient is happy with the cosmetic finish. Ongoing training with the physiotherapist/occupational therapist is important.

These videos show the fitting, assessment and rehabilitation approaches for transhumeral amputation:

Summary

Upper limb prosthetics is a complex, specialist area. There are multiple solutions to individual problems, but often the simple solutions are most effective.