Modular: S-ROM Stem

Developed in the early 1980s, the S-ROM stem (DePuy, a Johnson & Johnson company, Warsaw, IN, USA) is a modular femoral prosthesis made of titanium alloy (Ti6Al4V). It is composed of a proximal component, called the sleeve, and a neck-to-distal component known as the stem. This prosthesis was developed to address the issue of mismatch between the proximal and distal shapes of the femoral medullary canal, which worked against the fit-and-fill concept of conventional cementless stems. The main concept behind its design is that the shape and size for each fit can be independently selected and combined [1]. The sleeve is coated with a single layer of pure titanium beads to achieve biological fixation. In addition, the sleeves come in a variety of shapes and sizes, and the thickness of the coating is press-fitted to the reaming size. The distal stem has a smooth surface to avoid “fixation” with the bone, which plays an important role in obtaining initial stability [2]. The combination of the claw structure, comprising eight longitudinal flutes with an under-reaming mechanism (the flute diameter of the stem is larger than the reaming diameter) provides strong rotational stability. In addition, the distal stem has a tuning fork-like shape (slot) to reduce rigidity, particularly in the direction of the femoral curvature [1, 2].