Establishing the Problem: Rationale

There is unmet need for transtibial prostheses for persons <18 years of age that are capable of growing with the minor; that is, the prosthesis is either easily replaceable or adjustable beyond what is currently provided, which must be replaced every 1 to 2 years when the child grows beyond the prosthesis’ range of adjustment or wears out the limb with continuous stress. A child will need frequent replacement of a transtibial prosthesis for two primary reasons: growth and activity.

According to the CDC and researchers at Worcester Polytechnic Institute, children between ages 2 and 14 may grow 5-10 cm per year. Although conventional transtibial prostheses are capable of adjustment--endoskeletal shanks can be adjusted by changing the internal piping, exoskeletal shanks can be adjusted incrementally with the addition of shims by a prosthetist, and shoe insert may be added for both types of shanks--these adjustments have their limitations, and the child will require a new prosthesis given how rapidly they grow, both in height and weight.

People under 18 years of age also tend to be very active, putting more strain on their joints and requiring a higher range of motion. With continuous use, either sustained moderate pressure (i.e. walking, standing, etc.) or intermittent pressure (i.e. jumping, running, etc.), the prosthesis will exhibit a weakened shank, wear on movable components, and a less aesthetically pleasing external finish.

Frequent replacement of the prostheses should not be a problem; replacements do exist for all four components of a below-knee prosthesis (ankle-foot assemblies, shanks, below-knee sockets, below-knee prosthetic suspensions), but patients and families face financial restrictions in most cases. Prostheses are expensive (usually upward of $5,000) and frequent replacement is burdensome. Patients who require frequent replacements often deal with restrictions from their primary third-party payer. In some cases, children are denied financial reimbursement from insurers and must decline a prosthesis that their families can’t afford.