Objective: This study describes differentiating prosthetic feet designs fitted to bone-anchored transtibial prostheses based on an automated characterization of ankle stiffness profile relying on direct loading measurements. The objectives were, first, to present a process characterizing stiffness using innovative macro, meso, and micro analyses, second, to present stiffness profiles for feet with and without anthropomorphic designs, where anthropomorphicity is defined as a similarity of the moment-angle dependency in prosthetic and in the anatomical ankle, and third, to determine the sensitivity of characterization. Methods: Three participants walked consecutively, with two instrumented bone-anchored prostheses, including their own prosthetic feet and free-flow foot, meeting the anthropomorphicity criterion by design. Angle of dorsiflexion was extracted from video footage. Bending moment was recorded using multi-axis transducer attached to osseointegrated fixation. The automated characterization of stiffness involved a 12-step process relying on data-based criterion. Results: The meso analyses confirmed bilinear behavior of moment-angle curves with Index of Anthropomorphicity of -2.966 ± 2.369 Nm/Deg and 2.681 ± 1.089 Nm/Deg indicating a convex and concave shape of usual and free-flow feet without and with anthropomorphic designs, respectively. Conclusions: The proposed straightforward meso analysis of the stiffness was capable to report clinical meaningful differences sensitive to feet's anthropomorphicity. Results confirmed the benefits for clinicians to rely on direct loading measurement providing individualized complementary insight into impact of components. Significance: This work could assist the development of standards and guidelines for the manufacturing and safe fitting of components to a growing population requiring transtibial prostheses with socket or direct skeletal attachment worldwide.

Two decades after introducing threaded titanium dental implants, Dr. Per-Ingvar Brånemark used a similar technique in the 1980s to pioneer the direct skeletal attachment (DSA) of limb prostheses. He and his colleagues used convincing clinical experience to overcome the skepticism of their peers, affording a new dimension of prosthetic rehabilitation to almost 100 individuals with amputation. As a result, more research has been initiated worldwide to move DSA to a level of greater safety, longevity, and reliability. This review highlights the trends and milestones in current DSA development. It also identifies ideas from previous studies in various fields that may be useful in future DSA development.

This article presents recent results in the development of the skin and bone integrated pylon (SBIP) intended for direct skeletal attachment of limb prostheses. In our previous studies of the porous SBIP-1 and SBIP-2 prototypes, the bond site between the porous pylons and residuum bone and skin did not show the inflammation characteristically observed when solid pylons are used. At the same time, porosity diminished the strength of the pylon. To find a reasonable balance between the biological conductivity and the strength of the porous pylon, we developed a mathematical model of the composite permeable structure. A novel manufacturing process was implemented, and the new SBIP-3 prototype was tested mechanically. The minimal strength requirements established earlier for the SBIP were exceeded threefold. The first histopathological analysis of skin, bone, and the implanted SBIP-2 pylons was conducted on two rats and one cat. The histopathological analysis provided new evidence of inflammation-free, deep ingrowth of skin and bone cells throughout the SBIP structure.

Direct recordings were made of electrical signals emanating from the muscles in a rabbit's residuum. The signals were transmitted via wires attached on one end to the muscles, and on the other to an external recording system. The cable was held in a titanium tube inside a pylon that had been transcutaneously implanted into the residuum's bone. The tube was surrounded by porous titanium cladding to enhance its bond with the bone and with the skin of the residuum. This study was the first known attempt to merge the technology of direct skeletal attachment of limb prostheses with the technology of neuromuscular control of prostheses, providing a safe and reliable passage of the electrical signal from the muscles inside the residuum to the outside recording system.