16 Transhumeral Prosthesis Project Critique Guidelines
***During your critique, you are expected to identify the fitting problems, state the reason for the problem and describe a possible solution to resolve the problem. If you fail to identify a problem, you will be marked down.
Use this step-wise process to systematically evaluate the fit and operation the prosthesis.
Approximate force and displacement to operate the TD and prosthetic elbow are as follows.
| Operation | Force (lbs.) | Displacement (in) |
| Forearm flexion (no load on hook) | 9 | 2-2.5 |
| Prehension, VC hook | 9-35 | 1.5-2” |
| Prehension, VO hook | 10-20 | 1.5 |
| Elbow lock | 2-4 | 1/2-3/4” |
| Upper Limb Prosthetics, Prosthetist’s Supplement, New York University Medical Center |
Need a total of ~4.5” excursion to operate TD and elbow of transhumeral prosthesis with dual control cable.
| Control motions | Force (lbs.) | Excursion capability (in) |
| Glenohumeral flexion | 56 lbs. | 5.3” |
| Protraction | 49 lbs. | 1.6” |
| Glenohumeral extension | ||
| Glenohumeral abduction | ||
| Shoulder depression | 44 lbs. | 1.1” |
| Chest expansion |
Initial location of lift tab: 1¼-1½” distal and 1” anterior to elbow joint center
NYU recommends that the lift tab be approximately 1¼” distal from the elbow center and approximately 1 inch long. In general, the forearm lift tab needs to be close to the axis of rotation in order to minimize excursion required for use, but the closer it gets to the axis the longer the lift tab needs to be in order to reduce the force required.
Depending on the patient’s needs and abilities, adjustments may be made to the distance from the axis and the length of the lift tab.
Initial location of base plate: 25 mm proximal to the distal end of the humerus at the postero-lateral aspect of the mid-humerus.
The baseplate and retainer should be positioned for maximum efficiency for forces transmitted and excursion required. Moving the baseplate more distal and posterior will require less excursion and more force. Moving the baseplate more anterior and lateral will require more excursion and less force.
Two base plates may be used to lead the cable in the smoothest line from the control attachment strap to the lift tab, placing it anterior to the elbow joint center.
***The cable should lie anterior to the elbow joint axis!