A ligament's strength and flexibility are determined by its unique ratio of collagen and elastin proteins.

Ligaments are dense connective tissues primarily composed of Type I collagen fibers and elastic fibers. Collagen provides high tensile strength, with a modulus of elasticity reaching approximately 1.2 gigapascals. This allows ligaments like the Anterior Cruciate Ligament (ACL) to resist forces that would otherwise cause joint dislocation. Elastin is a highly insoluble polymer that can stretch up to 150% of its original length without breaking. In the human body, the ligamentum flavum in the spine contains nearly 60% to 80% elastin. This high concentration allows the spine to flex and extend safely while protecting the spinal cord. The specific ratio of these proteins is regulated by fibroblasts, which are specialized cells that synthesize the extracellular matrix. Research published in the Journal of Anatomy highlights that genetic factors, such as variations in the COL1A1 gene, influence collagen production. These variations can result in joint hypermobility syndrome, where individuals possess significantly more elastin or less dense collagen. Biomechanical studies show that as we age, the ratio of these proteins shifts and cross-linking increases. This process makes ligaments stiffer and more prone to injury. Understanding these protein concentrations helps orthopedic surgeons develop better synthetic grafts for ligament reconstruction surgeries.