## 2 Classification of Compression Garments and Specific Requirements
There are different technologies for manufacturing compression stockings that determine the compression class of the product. Compression stockings produced on a flat knitting machine can reach a higher compression class (3-4 classes) than that knitted on a circular knitting machine (1-3 classes) [17]. However, circular knitting is able to propose seamless products. Similar to compression stockings, knitted orthopaedic compression supports can be divided by purpose: prevention, rehabilitation or postoperative supports [41]. Compression support is defined as a corrective or orthopaedic item intended to grip or support any movable part of the body in the correct position and allow movement of that body part. The main difference between these groups is the intensity of compression generated by the support. Preventive compression support may assist both as sportswear and as a textile for medical applications. Nevertheless, medical supports may be applied for the same body part, though not for compression therapy purposes. The compression rate of the orthopaedic compression support is usually in the range of 20-25 mmHg [42]. Conventionally, all these products have various distinct applications. The range of orthopaedic supports is very wide. This group includes supports for neck, shoulder, wrists, elbows, hips, thighs, wrists, back, knees, legs, ankles and feet. Such supports not only fix the limb, but also hold, heat, stabilise, reduce pain, and play a different role, depending on the cause of the problem. The knee joint is the largest joint of the human body in terms of joint surface area and capsule size. Usually, it gets very heavy workloads. Regardless of its size, this joint is structurally weak. Because of its joint anatomy, large external forces and high function demands, the knee is one of the most commonly injured joints [43; 44]. Knee supports are generally divided into three groups: functional preventive supports, post-trauma supports, and post-operative supports. Information from different manufacturers was compared and the results of the analysis are presented in Table 4. Differently from the previous classification, in this case the similar application (e.g., knee support) but different purposes of the indications of products were analysed. \begin{table}
\begin{tabular}{c c} \hline \hline
**Support** & **Description** & **Functionality** \\ \hline \hline \multicolumn{3}{c}{Functional Prevention} \\ \hline \hline \multirow{3}{*}{Compression knee support} & The brace does not prevent movement, reduces the risk of injuries and is designed to be used during motion. Indicated for knee joint stabilisation, arthrosis of the knee joint, arthritis, osteoarthritis, synovitis, chondrites, etc. [20; 45]. \\ \cline{1-1}  & Compression knee support with silicon ring & Viscoelastic insert improves blood circulation and ensures knee patellar fixation and stabilisation in the correct position [20; 46]. Indicated for cartilage disease, deficient knee patella position of the knee joint ligaments and muscle strains, arthrosis, osteoarthritis, and injury prevention [11; 20]. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Analysis of applications and purposes of knee supports and braces. \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Standard**} & \multicolumn{4}{c}{**Compression Class**} \\ \cline{2-5}  & **I** & **II** & **III** & **IV** \\ \cline{2-5}  & \multicolumn{4}{c}{**Generated Compression, mmHg**} \\ \hline Great Britain BSI [34] & 14–17 & 18–24 & 25–36 & \textgreater{}36 \\ \hline Germany RAL-GZ-387/1:2008 [38] & 15–21 & 23–32 & 34–46 & \textgreater{}49 \\ \hline France AS-QUAL [37] & 10–15 & 15–20 & 20–36 & \textgreater{}36 \\ \hline Unified European CEN [35] & 15–21 & 23–32 & 34–36 & \textgreater{}49 \\ \hline USA (based on European Standards) [36] & 15–20 & 20–30 & 30–40 & \textgreater{}40 \\ \hline USA HCPCS [36] & & 18–30 & 30–40 & 40–50 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Compression class standards [39; 40].