Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Periarticular Ligamentous Tissue: A Biochemical and Physiologic Assessment-Key Points

Key Points

  • Although tendons and ligaments are composed primarily of fibrillar collagens, they have entirely different functions. Tendons are a conduit, connecting muscle to bone. Ligaments are short bands of fibrous tissue that bind bone to bone.
  • Collagen is the single most abundant animal protein in mammals. Collagen molecules assemble into characteristic fibers responsible for the functional integrity of tissues such as bone, cartilage, skin, ligament, and tendon.
  • The medial collateral ligament (MCL) of the knee is notable for rod-shaped and spindle-shaped cells that are intermediate in length compared with patellar tendon and anterior cruciate ligament (ACL) cells. The cellular morphological characteristics of the MCL are those of all fibroblasts, whereas the ACL cellular characteristics are similar to fibrocartilage cells.
  • A distinct form of collagen in cartilage, now known as Type II collage, was discovered about 30 years ago. Since then, many other unique molecular species have been observed. Types I, II, III, V, and XI collagen are categorized as fiber-forming collagens. They all exhibit lengthy, uninterrupted collagenous domains and are first synthesized as biosynthetic precursors (procollagens).
  • Proteoglycans consist of small amounts of protein bound to negatively charged polysaccharide chains referred to as glycosaminoglycans (GAGs). In articular cartilage, proteoglycans form a large portion of the macromolecular framework, but in ligaments they form only a small portion of this framework.

The ligaments of the knee are well-designed for their role in the maintenance of normal joint kinematics, with each ligament oriented in the direction needed to provide joint stability. Ligaments are well-designed connective tissues. Their densely packed collagen fiber bundles are arrayed in parallel along the length of the tissue substance to allow for the most efficient resistance of tensile loads.

Ligament insertions to bone are also well-adapted to their intended function. Force dissipation is achieved through a gradual transition from ligament to fibrocartilage to bone. Disruption is less likely to occur in this transition region than in the bone or peri-insertional tissue substance.

For many years, tendons and ligaments have been classified together as dense, regularly arranged connective tissue . Although tendons and ligaments are composed primarily of fibrillar collagens, they have entirely different functions. Tendons are a conduit, connecting muscle to bone, thereby allowing movement of a joint complex through muscle contraction or relaxation.

Ligaments are short bands of fibrous tissue that bind bone to bone and provide support for internal organs. In concert with the bony geometry and the dynamic effects of muscle and tendon ligaments limit and guide joint motion.

Collagen is the single most abundant animal protein in mammals, accounting for up to 30% of all proteins . Collagen molecules assemble into characteristic fibers responsible for the functional integrity of tissues such as bone, cartilage, skin, ligament, and tendon. They contribute a structural framework for most organs. Crosslinks between
adjacent molecules are a prerequisite for the collagen fibers to withstand the physical stresses to which they are exposed.

A variety of human conditions, normal and pathologic, involve the ability of tissues to repair and regenerate their collagenous framework. Many disabling conditions result from changes in the nature and organization of collagen.

Comments are closed.