Understanding Kinematic Changes in Prosthetics

At Marins Med we analyze the science of human motion. Kinematics is a branch of mechanics that studies the motion of objects without considering the forces that cause this motion. In the context of prosthetics, kinematic changes refer to the alterations in the movement patterns of the prosthetic limb and the user's body as they learn to use the device.

Key Aspects of Kinematic Changes

1. Movement Time: This is the duration taken to complete a specific movement or      task. For prosthetic users, a reduction in movement time indicates improved efficiency and skill in using the device.
2. Velocity: This refers to the speed at which a movement is performed. In prosthetics,      an increase in the velocity of movements, such as hook closing, suggests that the user is becoming more adept at controlling the prosthesis.
3. Trajectory: This is the path that the prosthetic limb follows during a movement. As      users become more skilled, their movement trajectories tend to become smoother and more direct, indicating better control and coordination.
4. Acceleration: This is the rate of change of velocity. In prosthetics, improvements in      acceleration can show enhanced responsiveness and control of the prosthetic limb.
5. Joint Angles: This refers to the angles between different segments of the      prosthetic limb and the user's body during movement. Optimal joint angles can indicate improved ergonomics and comfort in using the prosthesis.

Practical Implications

For body-powered prosthesis users, kinematic changes are crucial indicators of progress and learning. As users practice and become more familiar with their prosthetic devices, they typically exhibit:

• Decreased Movement Times: Faster task completion as they become more proficient.
• Increased Hook Closing Velocities: Faster and more efficient grasping motions.
• Smoother Trajectories: More fluid and controlled movements.

These kinematic changes are essential for improving the functional performance and overall usability of the prosthetic device, leading to better integration into the user's daily activities.

Influence of Terminal Devices on Kinematic Outcomes

While the prosthetic limb as a whole is crucial, the terminal device (such as the hook or hand) plays a significant role in determining the kinematic outcomes. Different terminal devices have unique characteristics that can influence movement patterns and efficiency.

1. Voluntary Closing (VC) Devices: As used in the study, VC devices like the TRS VC      Hook (Grip 3) require the user to actively close the hook by pulling on a  cable. This design allows for fine control over gripping force and speed, leading to more precise movements. Users can develop better kinematic outcomes such as faster hook closing times and smoother grasping trajectories.
2. Voluntary Opening (VO) Devices: These devices remain closed by default and      require the user to pull the cable to open the hook. VO devices can provide a stable grip once the object is held, potentially improving kinematic outcomes related to holding and manipulating objects over longer  periods.
3. Self-Actuated Locking Mechanisms: Incorporating a self-actuated locking mechanism into the terminal device could significantly enhance kinematic outcomes.      The ProHensor (ProHook), for instance, is a Voluntary Closing and Locking (VC&L) Device created by Marins Med. Such a mechanism would allow users to lock the device in a closed position without continuous effort, reducing fatigue and enabling more efficient use of the prosthetic limb. This could lead to:
   • Enhanced Grip Stability: Users can maintain a secure grip on objects without       ongoing exertion, improving movement efficiency and task performance.
   • Improved Task Performance: The ability to lock the device could result in more       consistent and reliable execution of tasks, particularly those requiring sustained grip.
   • Increased Confidence and Acceptance: Enhanced functionality and ease of use may boost user confidence and acceptance, addressing common issues related to prosthetic rejection.

Conclusion

Understanding and measuring kinematic changes provide valuable insights into the effectiveness of prosthetic training programs and the development of user-friendly prosthetic devices. By focusing on these changes, researchers and developers can create more effective training protocols and design advanced prosthetic solutions that enhance the quality of life for users. Terminal devices, especially those with advanced features like self-actuated locking mechanisms, play a crucial role in optimizing these kinematic outcomes and ensuring that prosthetic users can perform daily tasks with greater ease and efficiency.