Comparative Mechanical Testing of Knitted Compression Garments’ Dosage Distribution and Stiffness

Introduction: Knitted compression garments are manufactured with standardized pressure ranges, reported as ankle dosage only, in mmHg.  However, their effectiveness is also dependent on stiffness (references 1-10), and distribution of dosage may also play a role. Unfortunately, these parameters are not reported.  Therapeutic ranges could be determined through comparative mechanical testing.

Methods: Standardized mechanical tests were conducted on garments in Circular Knit (CK), custom Flat Knit (FK), and new Stiffer Circular Knit (SCK) categories. Pressure and stiffness values were verified at the foot, ankle, calf, and thigh, using a Zwick/Roell device (constant rate of extension) and integrated computer software.  All products tested were of the same dosage (30-40mmHg). CK and SCK were the exact same size, and custom FK of similar size.

Results: All garments were verified to have 100% of the dosage at the ankle, consistent with garment labeling. CK garments had on average 47%, 55% and 27% at the foot, calf and thigh, respectively, relative to the ankle dosage. SCK average dosages were 71%, 68%, 43% at the foot, calf and thigh, respectively.  FK were 89% and 76% at the calf and thigh, respectively (foot measurements not taken at time of study). Average stiffness at the ankle measured 1.37, 3.18, and 6.00 for CK, SCK and FK, respectively.  Standard deviation was similar within +/- 1.00 for all product categories.

Discussion: Effectiveness of compression garments varies based on compression dosage, stiffness and potentially dosage distribution.  In this study, garments of the exact same dosage had very different dosage distributions and stiffness levels. Our understanding of the different presentations of edemas continues to evolve, and new constructs for compression garment selection must evolve too. Stiffness and dosage distribution reporting, in addition to compression dosage, may help clinicians determine clinical efficacy.