Abstract
For primary hip arthroplasty contemporary acetabular component options available from across multiple manufacturers have evolved over the years to provide several common and widely available features and a few unique options designed to address the main clinical problems that have plagued hip arthroplasty in the past. These include the main causes of failure of THA generally, and of acetabular components in particular: fixation, wear, instability, and infection. The design and implant options that have been made available vary in how effectively they have “solved” the problem in question and occasionally have created new problems or have been associated with major tradeoffs and disadvantages.
Fixation: Cementless fixation of the socket has largely supplanted cemented fixation in North America. First generation ingrowth materials for cementless sockets including beads, plasma spraying, and wire mesh, have given way to enhanced more highly porous materials. The advent of rapid prototyping and 3-D printing of highly porous titanium (and other) materials has sparked a wave of various new orthopaedic implant designs including for the acetabulum.
Wear: Polyethylene wear and the resulting osteolysis problems seen in hip arthroplasty in the 1980's and 90's spawned a competition between 3 technologies over the optimal enhanced wear couple for THA: Metal-on-Metal (MOM), Ceramic-on-Ceramic, and Metal/Ceramic-on-Highly Crosslinked Polyethylene. Metal-on-Metal surface replacement and MOM THA were designed to reduce wear and also allow very large heads and potentially enhanced hip stability. Unfortunately, after wide adoption, subsequent problems occurred and this ongoing disaster has resulted in the rapid disappearance of virtually all MOM designs. Ceramic-on-Ceramic articulations achieve very low wear rates, but with lower tolerances for imperfect implant positioning. The potential for stripe wear, audible squeaking, rare breakage problems, and much greater expense have limited usage in the US, though this articulation is still preferred by some surgeons for selected very young patients. Ceramic- or Chrome Cobalt-on-Highly Crosslinked Polyethylene has emerged as the most widely used articulation in the US and has excellent wear performance with no demonstrable osteolysis over the first decade. More recent modifications of crosslinking methods and use of Vitamin E as an antioxidant, it is hoped, will further improve wear performance and mechanical properties.
Instability: Instability of the hip (subluxation or frank dislocation) remains one of the most common complications of THA, especially early. Acetabular component and insert options available to prevent instability (or treat it in the revision setting) include: 1) Optimal cup version and inclination (so called “safe zone”); 2) Prevent femoral component impingement against socket or liner rim; 3) Face changing elevated liner; 4) Liner to allow large fixed head (32 mm or > depending on cup size); 5) Dual mobility liner; 6) Tripolar construct (small bipolar inside a matched liner for a 40 mm or larger head); 7) Constrained liner (various designs).
Infection: There are currently a very limited number of acetabular component or liner options available to attempt to reduce the risk of infection or assist as adjunctive measures in treating the infected arthroplasty, but this is an area of active research and implant design effort.
