1. Technical Field
The present disclosure relates to acetabular implants for hip replacement surgery. In particular, the present disclosure relates to acetabular implants including a shell component and alternative bearing components interchangeably engageable with the shell component to provide a choice of bearing materials.
2. Description of the Related Art
Total hip replacement surgery is commonly performed to alleviate pain and loss of function in injured or diseased hip joints. During this surgery, the articulating surfaces of the hip joint are replaced with prosthetic bearing components. The replacement components generally include a femoral component having a convex bearing surface and an acetabular cup component having a mating concave bearing surface.
Modular prosthetic components have become popular because they allow the surgeon to assemble components in a variety of configurations at the time of surgery to meet specific patient needs and surgeon preferences. For example, modular acetabular components generally include separate shell and liner components that can be assembled in a variety of configurations of shell surface finish, shell outer diameter, liner inner diameter, and liner bearing material. With a modular acetabular component, it is desirable to lock the shell and liner together to prevent expulsion of the liner and to minimize debris producing wear between them. Typically, the engagement mechanism is formed adjacent the equator of a hemispherical shell and liner to maximize the engagement area and the resulting holding power of the engagement mechanism.
Various liner bearing materials are in use. The liners vary in hardness, friction coefficient with different paired ball heads, weight, and wear resistance. Polymers, including ultrahigh molecular weight polyethylene (UHMWPE), are commonly used as bearing materials paired with an opposing metal, ceramic, or other composition ball head. The wear resistance of UHMWPE has been improved by irradiating it to cause changes in its chemical and mechanical properties. As the wear properties are improved, the bulk physical properties also change. Other materials, including metals and ceramics, have also been used for acetabular bearings. These materials vary from one another in terms of their hardness, resilience, brittleness, and other physical properties. Because of this variation, various mechanisms have been developed for engaging acetabular liners with their mating shells. Different engagement mechanisms are suitable for different liner and shell material combinations. These engagement mechanisms include snap-fit, cylindrical press-fit, taper-fit, threaded engagement, and other suitable locking mechanisms. It is desirable to be able to alternately fit different liners into a common shell to reduce inventory while allowing surgeon choice in liner selection. It is also desirable to allow intraoperatively changing from one liner to another without having to remove a shell that has already been placed in the surgical site during a primary surgery, or one that has become well fixed and only needs liner replacement in a revision surgery.
U.S. Pat. No. 6,475,243 issued to Sheldon et al. on Nov. 5, 2002 (the “'243 patent”). The '243 patent discloses an acetabular cup assembly that allows pre-operative or inter-operative selection and securement of a bearing member within a shell member. The shell is metallic, while the bearing insert is in the form of a plastic bearing member. The assembly of the '243 patent includes a securing mechanism including an annular recess formed in the shell and a complementary annular rib that seats within the annular recess. In this assembly, the preferred material for the bearing member is polyethylene.
Alternatively, the '243 patent discloses a sleeve that may be secured within the shell by locking of tapered seating surfaces. A bearing member is secured to the sleeve with a tapered securement surface. The preferred material for the sleeve is commercially pure titanium. A recess may be formed in the tapered seating surface so that engagement of tapered seating surfaces occurs along two segments having generally the same axial length.
U.S. Pat. No. 6,610,097 issued to Serbousek et al. on Aug. 26, 2003 (the “'097 patent”). The '097 patent discloses a shell, a liner and a bearing. The bearing is coupled to the liner to form a subassembly by cooling the bearing, such as with liquid nitrogen, to shrink the size of the bearing, then press-fitting the bearing into the liner and allowing the bearing to warm and return to a larger size. The bearing and liner are fastened together in a fixed and locked position to form the bearing/liner subassembly. The liner provides a metal taper surface that forms a metal-to-metal locking connection between the subassembly and the shell.