Upper-Limb Prosthetic Hands and Terminal Devices

Upper-limb prosthetic hands and terminal devices are the end components of an arm prosthesis that interact with objects, providing grasp, pinch, or hook-style prehension. They differ both in form — anatomical hands versus split hooks and tools — and in how the user controls them, ranging from body-powered cable systems to myoelectric devices driven by muscle signals.

Definition

An upper-limb terminal device is the component at the end of an arm prosthesis that performs prehension — a prosthetic hand, hook, or specialized tool — and may be operated by body power through a harness and cable or by externally powered (myoelectric) control driven by muscle signals.

Scope

This topic covers the function and design of upper-limb terminal devices, the principal control strategies (body-powered and myoelectric, including pattern recognition and targeted muscle reinnervation), and the trade-offs among dexterity, feedback, weight, and reliability. It is a reference overview of upper-limb componentry and control, not a prescription or fitting guide.

Core questions

• What grasp functions must an upper-limb terminal device provide, and how do hands and hooks differ?
• How do body-powered and myoelectric control strategies operate?
• How do pattern recognition and targeted muscle reinnervation expand control of multifunction devices?
• What trade-offs exist among dexterity, feedback, weight, and reliability?

Key concepts

• Terminal device (hand, hook, tool)
• Prehension and grasp patterns
• Body-powered (cable-operated) control
• Myoelectric (externally powered) control
• Direct control versus pattern recognition
• Targeted muscle reinnervation
• Sensory feedback and device weight

Mechanisms

A terminal device produces prehension through opposing surfaces (fingers or hook tines) that open and close. Body-powered devices use a harness and cable so that shoulder or scapular motion opens or closes the device, giving the user some inherent force feedback through the cable. Myoelectric devices detect electrical signals from residual muscles via surface electrodes and translate them into device actions; in direct control a pair of muscle sites drives open and close, while pattern-recognition control interprets coordinated patterns of muscle activity to select among more functions. Targeted muscle reinnervation surgically redirects residual nerves to spare muscles, creating additional intuitive control sites and improving the signals available for multifunction myoelectric control. Designs trade dexterity and number of grasps against weight, cost, robustness, and the limited sensory feedback that current devices provide.

Clinical relevance

Terminal-device choice and control strategy shape how well a person can perform daily tasks and how readily they adopt and continue using an upper-limb prosthesis, so understanding the options supports shared decisions in rehabilitation. This topic describes devices, control methods, and evidence for reference and education; it does not provide individual prescription, fitting, or surgical guidance.

Evidence & guidelines

Evidence on upper-limb prosthetic control includes controlled studies and a randomized clinical trial showing that, for selected users with targeted muscle reinnervation, pattern-recognition control can outperform conventional direct control on functional tasks. Much of the broader evidence consists of laboratory and small clinical studies, and high abandonment rates of upper-limb prostheses remain a recognised challenge in the field.

History

Upper-limb prostheses long relied on body-powered split hooks and hands operated by harness-and-cable systems. Myoelectric control using residual-muscle signals developed through the later twentieth century, and subsequent advances in multi-articulating hands, pattern-recognition control, and targeted muscle reinnervation aimed to expand the number of functions a user can command intuitively.

Debates

Do advanced myoelectric and multi-articulating hands outperform simpler devices in everyday use?

Controlled studies, including a randomized trial after targeted muscle reinnervation, show pattern-recognition control can outperform direct control on tasks, yet body-powered devices retain advantages in robustness, weight, and feedback, and high abandonment rates complicate claims of overall superiority.

Seminal works

• kuiken-2009
• hargrove-2017

Frequently asked questions

What is the difference between body-powered and myoelectric terminal devices?

Body-powered devices are operated mechanically through a harness and cable driven by body movement, while myoelectric devices use electrodes to detect muscle signals and electric motors to open and close the terminal device.

What is targeted muscle reinnervation?

It is a surgical procedure that redirects residual nerves to spare muscles so they generate additional control signals, which can provide more intuitive sites for controlling a multifunction myoelectric prosthesis.