3D-Printed Implants Improve Amputee Prosthetics Integration

A new study shows that three dimensional (3D) additive manufacturing (AM) printing technologies can be used to customize implant surface textures and geometries to match the specific anatomy of human amputees.

Researchers at the University of North Carolina (UNC, Chapel Hill, USA) and North Carolina State University (NC State, Raleigh, USA) conducted a study to evaluate electron beam melting (EBM) and direct metal laser sintering (DMLS) for the manufacture of titanium osseointegrated implants. While EBM produces only a coarse textured implant, DMLS can create either a fine or coarse textured surface. For the study, two cohorts of Sprague-Dawley rats received bilateral titanium implants in their distal femurs, and were followed for four weeks.

The first cohort animals received EBM implants transcortically in one femur and a DMLS implant in the contralateral femur. The second cohort received DMLS implants (either fine textured or coarse textured in order to mimic EBM) in the intramedullary canal of each femur. The researchers then compared the two AM methods and the resulting strength of bone integration, interlocking, and torque. The results showed substantial differences between the two methods, including osseointegration and torsional properties, bone volume fraction (BV/TV), and bone-implant contact (BIC).

The researchers found that fixation strength of coarse textured implants provided superior interlocking, relative to fine textured implants, without affecting BV/TV or BIC in both rat cohorts. The coarse EBM implants in the transcortical model demonstrated an 85% increase in removal torque relative to the fine DMLS textured implants. On the other hand, the thrust load in the intramedullary model saw a 35% increase from fine to coarse DMLS implants. The study was published in the June 2017 issue of 3D Printing and Additive Manufacturing.

“Osseointegrated implants transfer loads from native bone to a synthetic joint and can also function transdermally to provide a stable connection between the skeleton and the prostheses, eliminating many problems associated with socket prostheses,” concluded senior author Paul Weinhold, PhD, of UNC, and colleagues. “Additive manufacturing provides a cost-effective means to create patient-specific implants, and allows for customized textures for integration with bone and other tissues. Due to spatial resolution, DMLS can produce surfaces with a roughness comparable to EBM.”

Direct transcutaneous osseointegrated prostheses constitute an emerging alternative to traditional socket prostheses that offer a stable connection, and the elimination of dermal lesions caused by the socket-skin interface. Osseointegrated implants also transfer loads from the residual native bone to a synthetic joint and back to the opposing bone in total joint replacements. AM implants provide a cost-effective means to customize the shape of the implant to interface with a patient's unique bone morphology, and allow for the customization of the surface texture that integrates directly with the bone and other tissues.

Related Links:
University of North Carolina
North Carolina State University