Development and Verification of a Porous Acetabular Shell Design Manufactured Using Additive Technology.

INTRODUCTION: Porous surface acetabular shells have been successfully used in cementless total hip arthroplasty. Recent advances in additive manufacturing have provided opportunities to optimize the shell designs. The current study describes the design and verification of a new acetabular shell design. MATERIALS AND METHODS: Additive manufacturing technology was used to fabricate acetabular shells using Ti6Al4V powder. A large computed tomography (CT) database was used to verify the screw hole location to ensure the screw trajectories were directed in the safe zone. Benchtop stability tests were conducted to compare the fixation stability of the new shell design to a clinically successful design. RESULTS: Shells were designed with an average pore size of 434 microns, surface porosity of 76%, and a coefficient of friction of 1.2. The CT analysis of various shell orientations demonstrated that at least two useful screws were typically directed toward the acetabular safe zone. The sawbone testing showed that the fixation stability of the new shell was either better or equivalent to the clinically successful design under two different bone preparation conditions. CONCLUSIONS: Using additive manufacturing technology, thin walled acetabular shells were fabricated which allowed for at least two ancillary fixation screws in the safe zone. The thin walls enable the use of a 36mm femoral head with a 48mm diameter shell which may enhance the joint stability in small stature patients. The equivalent or better fixation stability of the new design indicates that good initial fixation may be expected in vivo.

Selective laser melting: a unit cell approach for the manufacture of porous, titanium, bone in-growth constructs, suitable for orthopedic applications. II. Randomized structures.

In this study, the unit cell approach, which has previously been demonstrated as a method of manufacturing porous components suitable for use as orthopedic implants, has been further developed to include randomized structures. These random structures may aid the bone in-growth process because of their similarity in appearance to trabecular bone and are shown to carry legacy properties that can be related back to the original unit cell on which they are ultimately based. In addition to this, it has been shown that randomization improves the mechanical properties of regular unit cell structures, resulting in anticipated improvements to both implant functionality and longevity. The study also evaluates the effect that a post process sinter cycle has on the components, outlines the improved mechanical properties that are attainable, and also the changes in both the macro and microstructure that occur.

Selective Laser Melting: a regular unit cell approach for the manufacture of porous, titanium, bone in-growth constructs, suitable for orthopedic applications.

In this study, a novel porous titanium structure for the purpose of bone in-growth has been designed, manufactured and evaluated. The structure was produced by Selective Laser Melting (SLM); a rapid manufacturing process capable of producing highly intricate, functionally graded parts. The technique described utilizes an approach based on a defined regular unit cell to design and produce structures with a large range of both physical and mechanical properties. These properties can be tailored to suit specific requirements; in particular, functionally graded structures with bone in-growth surfaces exhibiting properties comparable to those of human bone have been manufactured. The structures were manufactured and characterized by unit cell size, strand diameter, porosity, and compression strength. They exhibited a porosity (10-95%) dependant compression strength (0.5-350 Mpa) comparable to the typical naturally occurring range. It is also demonstrated that optimized structures have been produced that possesses ideal qualities for bone in-growth applications and that these structures can be applied in the production of orthopedic devices.