Podium (General) 06

The MechPro1 a Mechanical Prosthesis Developed for Below-Elbow Amputation

Abigail R. Tud, MD-MBA, FPOA1

Introduction: The National Council on Disability reported an approximate 44,000 Filipino amputees in the year 2000. Of these, lower extremity amputations were more common. Upper extremity amputations however, tend to have a larger effect on independence and activities of daily living. For most marginalized patients, loss of limb also means loss of productivity, translating to further financial constraints. Provision of artificial limbs may help avert such consequences, but the cost of commercially-available bionic devices for the upper extremity remain prohibitive. The development of a three-dimensional (3D)-printed mechanical prosthesis may provide patients with a reproducible, cost-effective alternative.

Case Report: A 16-year-old right-handed female sought consult for a large, bleeding left hand mass. Biopsy findings were consistent with Giant Cell Tumor of Bone. Magnetic resonance imaging revealed extensive tumor involvement of the second and third metacarpals, the proximal carpal row, and both dorsal and palmar peri-osseous spaces, as well as encasement of adjacent muscles, tendons and neurovascular bundles. A trans-radial amputation was performed, which healed unremarkably. Financial constraints coupled with the patient’s age prompted the authors to consider a low-cost alternative to commercially-available bionic devices. This led to the creation of a 3D-printed trans-radial artificial limb with haptic feedback. The device was composed of a 3D-printed nylon plastic shell housing mechanical components, powered by two standard double A batteries. An adhesive surface electrode attached to the volar surface of the forearm stump transmitted myoelectric impulses into analog pins within a microcontroller. Digital pins in the microcontroller sent output signals to a servo motor, which consisted of a direct current, potentiometer and control circuit. This servo motor was attached by gears to a control wheel, which converted force exerted into finger movement. The thumb was composed of a single unit which allowed for full flexion and extension in the transverse plane at 2the approximated metacarpophalangeal joint, while the remaining four fingers allowed for full flexion and extension in the sagittal plane at two joint approximations: the metacarpophalangeal and proximal interphalangeal joints. Using a combination of body- and electrically-powered mechanisms, the patient was able to pick up and hold common items such as a pen, her cellular phone and an egg.

Conclusion: Successful rehabilitation following upper-extremity amputations is imperative for patients to recover function, resume activities prior to surgery and remain productive members of society. For many patients, the use of artificial limbs can help ensure this. Technological advances in prosthetic devices have allowed for some patients to attain a degree of normal hand function and dexterity. Costs remain prohibitive for a majority of Filipino patients however, highlighting the need to develop highly-functional, light-weight artificial limbs that can eventually be mass-produced at a lower cost. The MechPro1 is a prototype that may eventually provide an alternative to commercially-available below-elbow bionic devices.

Key words: bionic arm, haptic feedback, hybrid prosthesis, transradial amputation