Orthopedics - Oleksa A.P. 2006

Examination of the Orthopedic Patient
Structural Elements of the Joint
Cartilage

Cartilage is a type of Connective Tissue. There are three main types:

1. Hyaline cartilage — covers the ends of long bones in diarthrodial joints.

2. Fibrocartilage — found in specific locations that are not diarthrodial joints.

3. Elastic cartilage — can be found in structures such as the tip of the Nose or the auricle of the ear.

According to Benninghoff, articular cartilage consists of four distinct zones:

— the superficial layer, also known as the tangential zone, formed by small, flat, round Cells arranged parallel to the joint surface;

— the transitional zone, composed of cells with an irregular round shape;

— the radial zone, formed by elongated cells oriented perpendicularly to the plane of the joint, with their number essentially determined by the thickness of the articular cartilage;

— the calcified zone, which is adjacent to the bone.

Between the cartilage cells within the hyaline ground substance lie fine fibrils that tightly encircle them; these fibrils run parallel to the joint surface in the tangential zone and perpendicularly to it in the radial zone. The hyaline matrix creates a glassy, smooth articular surface.

Articular cartilage ensures smooth joint motion because its resilient superficial layer is not only nourished but also continuously lubricated by synovial fluid. During movement and impact, resilient articular cartilage can compress and subsequently recover its original shape and surface Structure.

This shape deformation is driven by the flattening of chondrons, which are enclosed by fibrils; once the pressure on the contacting areas of the articular surfaces is released, they restore their shape under the hydrostatic pressure of the internal fluid.

However, the elasticity of cartilage varies across different joints and even within different areas of the same joint. For instance, cartilage in joint sockets is softer and varies in thickness, whereas the cartilage covering bone heads is denser.

Cartilage thickness also varies across different joints, reflecting functional demands, namely joint load, pressure, and friction. The greater the demands, the thicker and more resilient the cartilage. If contact between articulating cartilage surfaces is lost (for example, in untreated dislocations), the articular cartilage degenerates. Furthermore, articular cartilage undergoes retarded growth and pathological changes due to prolonged pressure on localized areas, which can occur with the application of plaster casts or limb axis misalignment.

Pathological alterations in the biochemical, enzymatic, and cytological COMPOSITION OF THE synovial fluid also adversely affect the condition of articular cartilage.

Hyaline cartilage is an aneural, avascular connective tissue composed of 70% Water and 30% Extracellular matrix and cells. The matrix consists of Collagen and glycosaminoglycans. Scattered throughout in small cavities known as lacunae are the cellular components — chondrocytes.

Chondrocytes play a vital role in maintaining healthy cartilage by producing matrix components. Hyaline cartilage receives most of its Nutrition through diffusion from the synovial fluid and the Vessels of the subchondral plate. Normal joint function depends entirely on the health of the hyaline cartilage. When fully hydrated, hyaline cartilage ensures frictionless movement across articular surfaces.