Biological structures like bones, tendons, and ligaments have mechanical properties that allow the body to move. Furthermore, bones, tendons, and ligaments are structurally, mechanically, and functionally related. Bone is connected to other bone with ligament. Tendons connect muscles to the bone, enabling movement. Both ligament and tendons are comprised primarily of collagen. However, both ligament and tendon have a unique hierarchical structure, in which the outer casing contains successive layers of inner material called fascicles. The structure of tendons and ligaments is not unlike that of a Russian doll. Although both tendons and ligaments have a similar hierarchical structure, they differ in the way the fascicles (including subfibrils, fibrils and fibers) are arranged. Their differential structural arrangement is impacts their different mechanical properties. Generally, ligaments are less tightly structured and therefore more elastic in nature. Tendon fibers, on the other hand, have more of a parallel arrangement with larger fibers. Ligament fibers typically remain crimped until they are stretched to their limit. When they are stretched to their limit, the ligaments will straighten and resist stretching past the point at which the joint’s integrity or stability will allow. If the ligament is stretched past this point, injury may result.

Articular cartilage is the tissue surrounding the ends of a bone where it connects to a joint. Healthy articular cartilage reduces friction to enable smooth, pain-free movement. Articular cartilage also...

Both tendons and ligaments also serve a similar function in controlling joint motion and regulating movement, friction, and pressure.
Bones contain both organic and inorganic materials. The inorganic materials in bone, primarily calcium, are what prevent the bone from deteriorating and what gives bones their natural strength. Organic materials in bone enable flexibility and weight distribution features over time. Unlike ligament, tendon, or cartilage, the weight of bone is not primarily water. However, bones do have fluid elements like marrow. Different bones in the body have different structures and compositions, depending on their function. The mechanical properties of each bone inform, and are informed by, their structures and compositions. For example, the bones in the leg and especially the femur carry almost all of the human body’s weight. Leg bones need to be particularly good at handling and distributing load stress. As a result, the femur’s mechanical structure is much different from that of the pelvis bone or any other bone in the body.

Tendons, ligaments, and articular cartilage can deteriorate over time. Joints also suffer from repetitive use, particularly the knee. The efficacy of tendons, ligaments, and articular cartilage can also be diminished via disuse or misuse. When ligaments heal after an injury, they almost never return to their pre-injury state, making injury prevention critical. The knee is…