Influence of orthopedic support structure and construction on compression and behavior during stress relaxation

Abstract

This work was focused on changes of the compression generated by knitted orthopedic supports during the stress relaxation in order to find in which period of the stress relaxation the most significant part of the compression is lost. The influence of knitted structure, elastomeric inlay-yarn insertion density and shape/orientation of the rigid element fixed on the fabric on the compression and its changes under the stress relaxation was also investigated in this study. 11 different knitted structures and constructions were used in this research. It was found that the higher density of elastomeric inlay-yarn insertion into the knitted structure is not only responsible for higher compression generation, but also makes compression degradation during the time slower. In addition, the higher pre-tension of the elastomeric inlay-yarn leads to the faster relaxation process. Moreover, the shape and orientation of the rigid element can significantly affect the compression generation, however behavior of all variants during the stress relaxation is very similar. Evaluation of the tensile force after at least 120-300 s of the stress relaxation has to be used in design algorithm of very different compression products and applied in estimation of the compression at different manufacturing stages of the product.

Classification, Structure and Construction of Functional Orthopaedic Compression Knits for Medical Application: A Review

“…These measurement methods are applied to the German standard RAL-GZ 387/1:2008 and British standard BS 6612:1985 [59]. The indirect (theoretical) method of determining compression is the compression calculation according to Laplace's Law [65,66]:…”

“…During the design and production processes of compression products, the modelling of the product must be based on the analysis of the compression phenomenon [66][67][68]. The mechanical properties of the materials used and, especially, the relaxation phenomenon that occurs during long-term wear must be evaluated, too.…”

“…The mechanical properties of the materials used and, especially, the relaxation phenomenon that occurs during long-term wear must be evaluated, too. Due to the stress relaxation, compression values, if compared the newly produced product and the same product after several hours of wearing, can differ significantly [66]. Currently, the design and production of compression products are based on an identical percentage decrease between the dimensions of the main structural perimeter compared with the corresponding values of the patient's body dimensions [19].…”

“…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].…”

“…The compressive properties of knitted fabrics are influenced by various factors: (a) raw material, i.e., ground yarn type and linear density and elastomeric yarn type; and (b) manufacturing process, i.e., the characteristics of the knitting machine and specific parameters of production process. Compression products are worn repeatedly many times; accordingly, the properties of resilience are equally important as elastic properties [66]. The recovery power of the product is used to evaluate its response to the body's movement immediately after the impact.…”