In this study, three-dimensional (3D) digital image correlation (DIC) was adopted to investigate the strain in the superficial medial collateral ligament (sMCL) of the human knee. To our knowledge, no reports or validation of 3D DIC measurement on human collagenous tissue exists. The first part of this research project focused on the validation of 3D DIC (1) as a highly accurate tool for non-contact full field strain analysis of human collagenous tissue. In the second part, 3D DIC was used to measure the strain patterns in the superficial medial collateral ligament (sMCL) of the native knee (2). In a third part, the strain pattern in the sMCL after total knee arthroplasty (TKA) in an ‘optimal’ (3) and with a proximalised joint line (4) was analysed. (1) Six fresh frozen human Achilles tendon specimens were mounted in a custom made rig for uni-axial loading. The accuracy and reproducibility of 3D DIC was compared to two linear variable differential transformers (LVDT's). (2) The strain pattern of the sMCL during the range of motion (ROM) was measured using 3D DIC in six fresh frozen cadaveric knees. The knees were mounted in a custom made rig, applying balanced tension to all muscle groups around the knee. The experiment was repeated after computer navigated implantation of a single radius posterior stabilised (PS) TKA in ‘optimal’ (3) and with a 4 mm proximalised joint line (4).Introduction
Methods
As human soft tissue is anisotropic, non-linear and inhomogeneous, its properties are difficult to characterize. Different methods have been described that are either based on contact or noncontact protocols. In this study, three-dimensional (3D) digital image correlation (DIC) was adopted to examine the mechanical behaviour of the human Achilles tendon. Despite its wide use in engineering research and its great potential for strain and displacement measurements in biological tissue, the reported biomedical applications are rather limited. To our knowledge, no validation of 3D DIC measurement on human tendon tissue exists. The first goal of this study was to determine the feasibility to evaluate the mechanical properties of the human Achilles tendon under uniaxial loading conditions with 3D Digital Image Correlation. The second goal was to compare the accuracy and reproducibility of the 3D DIC against two linear variable differential transformer (LVDT's). Six human Achilles tendon specimens were prepared out of fresh frozen lower limbs. Prior to preparation, all limbs underwent CT-scanning. Using Mimics software, the volume of the tendons and the cross sectional area at each level could be calculated. Subsequently, the Achilles tendons were mounted in a custom made rig for uni-axial loading. Tendons were prepared for 3D DIC measurements with a modified technique that enhanced contrast and improved the optimal resolution. Progressive static loading up to 628,3 N en subsequent unloading was performed. Two charge-coupled device camera's recorded images of each loading position for subsequent strain analysis. Two LVDT's were mounted next to the clamped tendon in order to record the displacement of the grips.Purpose
Methods
