Hip joint replacement based on linear cylindrical articulations for reduced wear : a radical change in design

Abstract

Hip replacement surgery is a common procedure for patients suffering from hip joint degeneration. However, wear of the implant components, particularly Ultra-High-Molecular- Weight Polyethylene (UHMWPE), remains a significant concern, often leading to complications such as osteolysis and implant loosening. This invention disclosure introduces a novel tri-axial hip replacement design aimed at addressing these issues. The design incorporates three orthogonal cylindrical articulations, each providing one rotational degree of freedom to replicate the natural movements of the hip joint. The prosthesis comprises two components made from UHMWPE (cup and rotator) and two components made from high-N stainless steel (flexor and abductor). Each articulation consists of metal-on-polyethylene bearing couples. Unlike traditional ball-and-socket implants, the novel design limits motion within each articulation to a single direction, taking advantage of friction-induced UHMWPE strain hardening. Moreover, cylindrical joints offer a larger contact surface area than their spherical counterparts, thereby reducing contact stresses. Mid-sized high-fidelity prototypes underwent wear resistance testing, demonstrating significantly superior performance compared to a commercial ball-and-socket implant of similar size tested in the same conditions. Moreover, a cadaveric implantation performed by experienced orthopaedic surgeons showed the implant has good stability even for postures requiring a wide range of motion. This innovative design represents a promising advancement in hip replacement technology, offering improved wear resistance and longevity, thus potentially reducing the need for revision surgeries and enhancing patient outcomes.