Neck-modular femoral stems for total hip arthroplasty.

Modular total hip arthroplasty (THA) components have evolved significantly as the success of uncemented femoral fixation has been proven. Current trends in the United States include widespread use of cementless components (acetabular and femoral), usually with monoblock femoral stems with modular heads. Femoral offset has been proven to play a vital role in hip abductor strength, hip range of motion, and hip stability. Also critical to hip stability is the orientation of the acetabular and femoral components. Thus, offset and component positioning are fundamental to success in THA. Modularity of the femoral neck has been proposed to aid in further customizing the THA component fit. Neck-modular stems enable the adjustment of leg length, femoral anteversion, and femoral offset independently of stem size. Modularity of the neck allows the surgeon to precisely match the anatomic characteristics of each patient to yield improved range of motion, stability, abductor strength, and leg length equality. Disadvantages are related to cost and the addition of another interface. Neck-modular femoral stems are not a new concept; however, as tough component manufacturing has advanced, these stems have been reintroduced to the armamentarium of the hip surgeon.