White-Tailed Deer as an Ex Vivo Knee Model: Joint Morphometry and ACL Rupture Strength

Reflected cross-polarized light microscopy as a method for measuring collagen fiber crimp in musculoskeletal tissues

Many musculoskeletal tissues are composed primarily of type I collagen, which takes on a periodic crimp morphology that allows large tensile strains in the tissue. The spatial period of collagen fiber crimp may be used to infer internal strains in a tissue and is typically measured using transmitted cross-polarized light imaging of thin slices. However, slicing may induce specimen distortion and precludes mechanical loading of the specimen during imaging. We hypothesized that reflected cross-polarized light imaging of thick tissue explants would yield crimp period measurements comparable to those obtained from transmitted light imaging of thin slices. We further hypothesized that these measurements would be sensitive to applied uniaxial strain in the fiber direction. These hypotheses were tested by imaging both intervertebral disc outer annulus fibrosus and medial collateral ligament tissue specimens. We found that both transmitted and reflected light yielded similar crimp period measurements for intervertebral disc tissue, with an overall average of 43.5 ± 11.5 μm. Reflected light yielded a significantly higher crimp period with lower variance than transmission through thin specimens (54.1 ± 10.6 μm versus 50.4 ± 16.0 μm) in the ligament. Upon application of axial tension, crimp periods in both fibers increased at a rate of approximately three times the applied strain (with 3.17% applied strain yielding a 9.64 ± 4.4% increase in crimp period in the disc and an 11.7 ± 3.7% increase in the ligament), indicating significant fibril sliding. In support of our hypotheses, these findings suggest that reflected cross-polarized light is a suitable method for measuring collagen fiber crimp in musculoskeletal tissues, both statically and under tension.

Cross-Sectional Area Measurement Techniques of Soft Tissue: A Literature Review

Evaluation of the biomechanical properties of soft tissues by measuring the stress-strain relationships has been the focus of numerous investigations. The accuracy of stress depends, in part, upon the determination of the cross-sectional area (CSA). However, the complex geometry and pliability of soft tissues, especially ligaments and tendons, make it difficult to obtain accurate CSA, and the development of CSA measurement methods of soft tissues continues. Early attempts to determine the CSA of soft tissues include gravimetric method, geometric approximation technique, area micrometer method, and microtomy technique. Since 1990, a series of new methods have emerged, including medical imaging techniques (e.g. magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging (USI)), laser techniques (e.g. the laser micrometer method, the linear laser scanner (LLS) technique, and the laser reflection system (LRS) method), molding techniques, and three-dimensional (3D) scanning techniques.

Proteoglycans contribute locally to swelling, but globally to compressive mechanics, in intact cervine medial meniscus

Loss of charged proteoglycans in the knee meniscus, which aid in the support of compressive loads by entraining water, is an effect of degeneration and is often associated with osteoarthritis. In healthy menisci, proteoglycan content is highest in the inner white zone and decreases towards the peripheral red zone. We hypothesized that loss of proteoglycans would reduce both osmotic swelling and compressive stiffness, spatially localized to the avascular white zone of the meniscus. This hypothesis was tested by targeted enzymatic digestion of proteoglycans using hyaluronidase in intact cervine medial menisci. Mechanics were quantified by creep indentation on the femoral surface. Osmotic swelling changes were assessed by measuring collagen fiber crimp period in the radial-axial plane in the lamellar layer along both the tibial and femoral contacting surfaces. All measurements were made in the inner, middle, and outer zones of the anterior, central, and posterior regions. Mechanical measurements showed variation in creep behavior with anatomical location, along with spatially uniform decreases in viscosity (average of 21%) and creep stiffness (average of 15%) with hyaluronidase treatment. Lamellar collagen crimp period was significantly decreased (average of 27%) by hyaluronidase, indicating a decrease in osmotic swelling, with the largest decreases seen in locations with the highest proteoglycan content. Taken together, these results suggest that while proteoglycans have localized effects on meniscus swelling, the resulting effect on compressive properties is distributed throughout the tissue.

Rise of the Pigs: Utilization of the Porcine Model to Study Musculoskeletal Biomechanics and Tissue Engineering During Skeletal Growth

Large animal models play an essential role in the study of tissue engineering and regenerative medicine (TERM), as well as biomechanics. The porcine model has been increasingly used to study the musculoskeletal system, including specific joints, such as the knee and temporomandibular joints, and tissues, such as bone, cartilage, and ligaments. In particular, pigs have been utilized to evaluate the role of skeletal growth on the biomechanics and engineered replacements of these joints and tissues. In this review, we explore the publication history of the use of pig models in biomechanics and TERM discuss interspecies comparative studies, highlight studies on the effect of skeletal growth and other biological considerations in the porcine model, and present challenges and emerging opportunities for using this model to study functional TERM.