Summary
Objectives: To design, manufacture and analyze custom implants with functional gradation in macrostructure
for attachment of amputation prostheses.
Methods: The external shape of the implant was designed by extracting geometrical data of
canine cadavers from computed tomography (CT) scans to suit the bone cavity. Three
generations of implant designs were developed and were optimized with the help of
fit/fill and mechanical performance of implant-cadaver bone assembly using CT analysis
and compression testing, respectively. A final optimized, custom Ti6Al4V alloy amputation
implant, with approximately 25% porosity in the proximal region and approximaltely
zero percent porosity in the distal region, was fabricated using Laser Engineered
Net Shaping (LENS™) – a laser based additive manufacturing technology.
Results: The proposed design changes in the second generation designs, in terms of refining
thresholds, increased the average fill of the bone cavity from 58% to 83%. Addition
of a flange between the stem and the head in the second generation designs resulted
in more than a seven-fold increase in the compressive load carrying capacity of the
assembly. Application of LENS™ in the fabrication of present custom fit Ti6Al4V alloy
implants enabled incorporation of 20 to 30% porosity in the proximal region and one
to two percent residual porosity in the distal portion of the implant.
Clinical significance: Patient specific prostheses having direct connection to the skeletal structure can
potentially aid in problems related to load transfer and proprioception in amputees.
Furthermore, application of LENS™ in the fabrication of custom implants can be faster
to incorporate site specific porosity and gradients for improving long-term stability.
Keywords
Custom implant - amputation prosthesis - solid freeform fabrication - rapid prototyping
- laser engineered net shaping
