## 4 Structure and Construction of Compression Orthopaedic Products
Knitted compression fabrics are made by knitting at least two types of yarns--ground yarn and elastomeric yarn--together. Ground yarn ensures stiffness and thickness. To generate compression and to achieve better performance of compression support, extra elastomeric yarns are inserted into the construction of a knit as inlaid, floated or plated yarns [66; 74; 81; 82]. Thus, taking into account what was said above, it can be summarised that the compressive properties of the orthopaedic product are ensured by the elastomer yarn, dimensional and shape stability is ensured by using synthetic yarns (polyamide or polyester) in the knitted structure, while comfort functionality can be reached by using natural yarns (they can be laid as a ground yarn in the plated or/and combined structure of the knit). The choice of knitting pattern is determined by the functional properties and intended purpose of the compression product. Theoretically, the elastomeric yarn can be introduced into the knitted structure in the following three ways: laying it in the form of a weft inlay yarn; laying it in the form of tucks; and knitting it into loops. The properties of the compression fabric, the structure of its surface and the location of the elastomeric yarn (inside the structure or on the surface of the fabric) will depend on the method of fixing the elastomeric yarn in the knitted structure. The method for securing the elastomeric yarn in the knitted fabric structure depends on the technological capabilities of the knitting equipment, the properties of the ground pattern and the requirements for the knitted product for a specific purpose. The optimal method is that which ensures reliable fastening of the elastomeric yarn in the knitted structure, also uniformity elasticity and dimensional stability of the knitted structure. Moreover, depending on the design of the rehabilitation product, fabrics with increased unidirectional or biaxial stretchability can be used for its manufacture. Modern products are made using both warp and weft-knitted elastic fabrics. In products made from knits of limited width (like corsetry, bandages or reinforcing tapes), usually warp-knitted tapes are used, in which the elastomeric component is introduced in the form of a weft inlay yarn. Such a knitted structure is stretchable only in one direction, however, depending on the relative position of other binding elements in the structure, it can be of different tightness [83]. Circular compression products are usually made on weft-knitting machines. They can be produced on the basis of single and double knitted patterns. Products made on the single needle bar knitting machine, i.e., on the basis of single patterns (such as compression prenatal underwent, stockings, knee socks, tights, stump covers) have a lower thickness and elastomeric yarns are fixed in the knitted structure in the form of tucks and/or knitted into loops together with the ground yarn using principle of a plated knitting [84]. Typically, compression knee pads and knee supports are knitted on the basis of double knitted patterns (using double needle bar knitting machines) that allow the elastomeric yarn to be inserted into the knitted structure in the form of an inlay yarn. Moreover, since the inlay yarn is not knitted into loops, there is more flexibility in choosing its linear density (thickness) depending on the requirements for the level of compression and the rigidity of the compression product. To ensure the longitudinal elasticity of a knitted product, elastomeric yarns can also be knitted into loops separately from the ground yarn. With this method of inserting an elastomeric component into the knitted structure, the functional properties of the product appear in the transverse direction, but such products also have elasticity in the longitudinal direction. The elastomeric yarn can be knitted into the structure by creating in turn loops and floats according to some particular pattern repeat.