Types of cartilage Main types of cartilage include articular (hyaline) cartilage fibrocartilage (tendon/ligament junction with bone) and fibroelastic cartilage (menisci) elastic cartilage (trachea) epiphyseal cartilage (growth plates) Cartilage biology Cartilage contents (avascular, aneural, and alymphatic) cells chondrocytes extracellular matrix water collagen proteoglycans noncollagenous proteins Cell differentiation cartilage is formed from mesenchymal stem cells designated towards the cartilagenous lineage multi-step process involving activation and migration of cells to necessary sites SOX-9 is a key transcription factor involved in the differentiation of cells towards the cartilage lineage parathyroid hormone (PTH) may have chondroprotective effects thought to be related to influence on indian hedgehog (IHH) signaling pathways affecting cartilage growth Metabolism regulated through mechanical stimulation pH of cartilage is 7.4 disruption in pH can lead to an abnormal cartilage structure Nutrition oxygen and other nutrients supplied to cartilage from synovial fluid diffusion Loading physiologic loading is chondroprotective underloading leads to cartilage thinning, tissue softening, and reduced proteoglycan content, leading to cartilage fibrillation, ulceration and erosion overloading leads to cartilage damage (in vitro only) has not been shown in clinical setting Articular (Hyaline) cartilage Complete Topic Location articular surfaces ribs nasal septum Composition water > collagen > proteoglycan > noncollagenous protein > cells water = 65% to 80% of mass of the cartilage Type II collagen = provides cartilagenous framework and tensile strength proteoglycans = function to provide compressive strength and attract water chondrocytes = produce collagen, proteoglycans, and enzymes Function decreases friction and distributes loads cartilage exhibits stress-shielding of the solid matrix components due to its high water content, the incompressibility of water, and the structural organization of the proteoglycan and collagen molecules Fibrocartilage Location tendon/ligament junction with bone pubic symphysis annulus fibrosis of the intervertebral disc menisci Composition fibrous cartilage Type I collagen (predominantly) extracellular matrix proteoglycans chondrocytes water fibroelastic cartilage fewer proteoglycans and glycoproteins compared to hyaline cartilage Function healing response to injury of articular cartilage including chondroplasty microfracture drilling abrasion arthroplasty compressive strength Elastic Cartilage Location auricle of external ear epiglottis auditory tube Composition chondrocytes surrounded by a thin collagenous network Type II collagen (predominantly) elastin fiber network extracellular matrix proteoglycans and glycoproteins chondrocytes water Function highly elastic designed to tolerate repetitive deformation Epiphyseal cartilage Location also known as the epiphyseal plate or epiphyseal ossification center between the epiphysis and metaphysis at each end of long bones Composition stacked chondrocytes are divided into different zones of maturation proteoglycans and growth factor (e.g.BMP-2) are found in the extracellular matrix between chondrocytes progressive chondrocyte maturation and calcification of the extracellular matirix infiltration of osteoprogenitor cells to produce osteoblasts and osteoid Histology of Epiphyseal cartilage Reserve zone Proliferative zone Hypertrophic zone Primary spongiosa Secondary spongiosa Function linear growth via endochondral ossification can allow extensive bone deformity remodeling potential