Published 7/1/2016
Amber Blake

Improving Prosthetics for Amputees

Study points to benefits of 3D printing, whole-body vibration
Complications commonly associated with traditional socket prostheses, such as pressure sores and instability, have led to an increased interest in improved methods for attaching prosthetic devices to amputees. One approach gaining popularity is the use of a direct transcutaneous osseointegrated implant that allows for a more stable connection to the skeleton, enabling greater control of the prosthetic limb and heightened sensory feedback.

Although these implants offer promise, they are not perfect, according to David Ruppert, a researcher at the University of North Carolina at Chapel Hill and North Carolina State University. "Unfortunately, these implants face several challenges that prevent their use outside of clinical trials," he said. "For example, the implants need to conform to patients' specific anatomy." In addition, he noted that the skin penetration of the implant is susceptible to infection. Furthermore, a 12-month rehabilitation period is required to produce a stable bone-implant interface.

Mr. Ruppert and his colleagues conducted research on two of these challenges: addressing the patients' specific anatomy and reducing the rehabilitation period. They presented their findings at the 2016 Orthopaedic Research Society (ORS) annual meeting.

The researchers compared the osseointegration of two types of textured surface implants—implants created by a 3D process and those machined with a standard threaded design—inserted bilaterally in the proximal tibiae of female rats. They also assessed whether use of whole-body low-magnitude, high-frequency vibration would reduce the integration period for both types of implants. Osseointegration was evaluated at 6 weeks using two-way analysis of variance (ANOVA) assessments.

 "Our findings showed that rough-textured implants created though 3D printing exhibit stronger bone integration than machine-threaded counterparts," said Mr. Ruppert. "This highlights the superiority of using 3D printing to not only produce custom designs, but also custom surfaces that interface with amputees' residual bones."

The researchers also found that vibrating the whole body at low magnitude and high frequency at a specific amplitude range increased bone density around both types of implants. These results demonstrate that whole-body vibration can be used to minimize bone loss during rehabilitation.

Previous work investigating fracture healing has indicated that low-intensity pulsed ultrasound (LIPUS) can be beneficial to bone healing through as yet undetermined mechanisms. It is also unclear if sufficient levels of the stimulus can reach the inner surfaces of the bone to stimulate bone healing.

"In the future, we will investigate the effects of LIPUS on bone integration into an implant to determine if further improvement on the rehabilitation period can be made," Mr. Ruppert explained. "We will also investigate whether there is a cumulative effect of using LIPUS in conjunction with vibration.

"Finally," he added, "we aim to validate additional methods of 3D printing to enhance the level of detail in implant design. Ultimately, we hope to improve the quality of life for amputees."

Mr. Ruppert's coauthors of "Osseointegration of EMB Textured and Threaded Implants through Whole Body Vibration" are Ola L.A. Harrysson; Denis J. Marcellin-Little; Laurence E. Dahners, MD; and Paul S. Weinhold, PhD.

Amber Blake is the ORS communications manager. She can be reached at blake@ors.org