The Use of Modularity in Total Hip Arthroplasty.

Modularity is defined as separation of a system into independent parts or modules that can be treated as logical and may be separated and recombined. Historically, the modularity represents the evolution of the concept of "low friction arthroplasty" developed by Sir J. Charnely in 1960. The disadvantage of a one-piece stem is the difficulty of restoring the biomechanical feature of the hip. Thus, the natural evolution was the introduction of modularity on both sides, the acetabulum and the femur. Modularity allows the surgeon to accurately match the anatomic characteristics of each patient to obtain improved range of motion, joint stability, abductor strength, and leg length equality. Disadvantages are related to the introduction of different interfaces, which could be sites of wear and corrosion. In accordance with the most recent literature, in primary total hip arthroplasty (THA) the modularity can be reduced to the head and the acetabular component, while a one-piece stem can manage the majority of cases. On the other hand, we believe that during revision surgery, a complete modularity is necessary.