Microanatomy of Cartilage, Tendon, Ligament and Joint PDF

Microanatomy of Cartilage, Tendon, Ligament and Joint Dr Georgios Paraschou DVM, DACVP, DipRCPath, MRCVS Slides courtesy of Dr Heather Fenton Spring 2024 Disclaimer: Images from this presentation come from different sources as indicated: McGavin’s Pat...

Microanatomy of Cartilage, Tendon, Ligament and Joint Dr Georgios Paraschou DVM, DACVP, DipRCPath, MRCVS Slides courtesy of Dr Heather Fenton Spring 2024 Disclaimer: Images from this presentation come from different sources as indicated: McGavin’s Pathologic Basis of Veterinary Disease, Tuft’s veterinary gross pathology image collection, Noah’s Arkive, web images, author’s own images or images from colleagues, etc. This presentation is intended to be for teaching purposes only, please do not distribute.  SKELETAL SYSTEM: FUNCTIONS Bone: Frame, protect, and support soft tissues (e. g. brain) Cartilage: Semi-rigid support to specific sites: present in many locations between bones, joints, ligaments, respiratory tree, and intervertebral discs. Acts as a shock absorber in menisci and intervertebral disks – Protects the ends of bones - there are three types of cartilage: hyaline,elastic, and fibrocartilage Ligaments provide stability of joints; connect bones to bones Tendons provide strong, flexible connections between muscles and bones. In athletes and overweight patients, pay attention to ligaments and tendons – they can get strained Joints: Spaces with fluid between bones; lubricated; provide varying degrees of movement and flexibility  SKELETAL SYSTEM: DIFFERENTIATION Originates from undifferentiated mesenchymal cells that can differentiate into various cell types: cartilage, bone, fibrous tissue, etc  CARTILAGE DIFFERENTIATION Differentiation and maturation is most advanced at the center of a mass of growing cartilage; immature at periphery (perichondrium). On completion of growth, the cartilage mass consists of chondrocytes embedded in a large amount of extracellular matrix. At the periphery of mature cartilage there is a zone of condensed connective tissue (perichondrium), containing elongated fusiform cells that resemble fibroblasts. These cells give rise to chondroblasts basicallyword saying surrounding cartilage  CARTILAGE Avascular semi-rigid form of connective tissue characterized by absence of blood vessels, lymphatic vessels and nerves (adults) – young animals have blood vessels in growing cartilage Supports soft tissues (e. g. ear, eyelid, trachea, and bronchi) Very important for LONGITUDINAL bone growth – Endochondral ossification Composed of cells (chondrocytes) that are embedded in an amorphous gel-like substance and connective tissue fibers, making this tissue resilient photo chondrocyte lacunar space matrix in intercellular region  CHONDROGENESIS a = embryonic mesenchyme b= proliferation and early differentiation in a of matrix c = chondroblasts separate from each other due to production d = multiplication of cartilage cells in aggregates 4 mature cartilage has slow cell turnover and replacement of cells Isogenous group: cluster of chondrocytes formed through the division of a progenitor cell; found in hyaline cartilage, elastic cartilage, and fibrocartilage CARTILAGE & BONE DIFFERENTIATION Endochondral ossification- cartilage in physes matures, dies, mineralized and forms scaffold to form bone – longitudinal growth of bones M P E  Growth plate (Physis) 1 B 2 Epiphysis 3 1 - zone of reserve/resting cells 2 - zone of proliferation Metaphysis with primary 3 - zone of hypertrophic cells spongiosa B – primary spongiosa – bone forms on dead mineralized cartilage “scaffold” TYPES of CARTILAGE based on the amount of collagen or elastic fibers present in the extracellular matrix, as well as the amount of GAGs Hyaline #1 Elastic Fibrocartilage Joints - articular cartilage Ear, Epiglottis Menisci Discs more rigi Ribs, Physes, Nose Flexibility needed Insertions of tendons & MOST common type ligaments  *Most abundant type of Locations of Hyaline Cartilage cartilage* Growth plates = physes Articular cartilage covers joint surfaces at costo- chondral junctions of the ribs, the nasal septum, larynx, tracheal rings, and bronchi. Fetal axial and appendicular skeleton  can regenerate ELASTIC CARTILAGE if have perichondrium can regenerate Has a perichondrium, chondroblasts and chondrocytes in large lacunae Contains abundant elastic fibers that stain darkly by specific dyes/stains Flexible tissue due to the presence of numerous bundles of branching elastic fibers in the cartilage matrix Found in the epiglottis and the corniculate and cuneiform processes of the arytenoid cartilage, in the external auditory canal and in the ear pinna Locations of Elastic Cartilage haspoorregenerative capacity FIBROCARTILAGE Lacks a perichondrium, thus does not have the capacity to regenerate. Fibrocartilage contains chondrocytes & lacunae Features are intermediate between cartilage and dense fibrous connective tissue ContainsType1 collagen fibers Located where support and tensile strength are required: Intervertebral discs (annulus fibrosus) menisci, insertions of tendons and ligaments,mandibular symphysis, pubic symphysis Locations of Fibrocartilage  Fibrocytes are mature and inactive Chondrocytes fibroblasts halo aroundchondrocyte vs no halo Fibrocartilage Intervertebral discs = annulus Connective tissue – collagen, dense. fibrosus, tendons, ligaments, skin, fascia, scar menisci, insertions of tendons,ligaments, tissue mandibular symphysis, pubic symphysis  PERICHONDRIUM articular Fibrocartilage don'thaveperichondrium The outer layer is composed of dense fibrous connective tissue; resembles mature fibroblasts.The inner layer is cellular and it is present in all hyaline cartilage except on articular surfaces. Inner layer is chondrogenic, contains cells with capacity to become chondroblasts (i. e. can regenerate) BUT not present in articular cartilage  GAGresponsibleforbasophilia Cartilage matrix Components include collagen, elastic fibers and proteoglycans(GAGs). Basophilia of cartilage matrix is due to high concentration of GAGs. The matrix near the clusters of chondrocytes (territorial) is more basophilic due to the greater amount of GAG than the matrix further away from the chondrocytes (interterritorial). GAGs = Sulfated polysaccharide units (GAGs = glycosaminoglycans) Examples of GAGs include chondroitin sulfate, keratan sulfate, dermatan sulfate, heparan sulfate and hyaluronan (hyaluronic acid in joint fluid) GAGs bound to a protein core form macromolecules called proteoglycans that are responsible for the strong and flexible property of cartilage – shock absorption Within the matrix GAGs are embedded at varying proportions of collagen and elastic fibers giving rise to the different types of cartilage: hyaline, elastic and fibro-cartilage Tendon muscle to bone Ligament bone to bone Function: attachments, flexibility TENDON Parallel bundles of type I Approximately 85% collagen- 98% type I collagen fibers in a 2% elastin tendon 1–5% proteoglycans  Tendon is primarily type I collagen, elastic and strong. Mature tendon contains cells that have a limited ability to regenerate. Following injury, a tendon lays down type III collagen, or scar tissue, which is stronger than type I, but stiffer and less-elastic. This makes it less flexible and prone to re-injure when the animal begins to stretch the tendon during strenuous work.  Types of Joints Fibrous Joints (Synarthroses): Bones or cartilages are united by fibrous tissue. There are three main types of fibrous joints 1. Sutures (cranial suture) 2. Syndesmosis (tibia-fibula) 3. Gomphosis (i. e. a tooth socket) Cartilaginous (Amphiarthrosis): Bones or cartilages united by hyaline cartilage (i. e. costrochondral joints) or fibrocartilage (i. e. pelvic and mandibular symphysis) Synovial (Diarthrosis/True joints): Unite two bone ends and are covered by articular cartilage and surrounded by a thick articular capsule (i. e. synovial joints of appendicular skeleton and vertebral joints) Bone surfacesin the jointcavityare coveredby hyaline cartilage (articular cartilage). The joint cavity consists of a capsule composed of a fibrous portion and a well vascularized synovial membrane lined by two types of cells: TypeA cell: phagocyticfunction–remove debris Type B cell: secrete hyaluronic acid, & protein complex (mucin) into synovial fluid = lubricant, protectant and nutrition to joints. Articular cartilage: Surface should be smooth; formed by Type II collagen and proteoglycans; lacks blood vessels and nerves (poor capacity for regeneration) - no nerves, blood or lymphatic vessels - firmly attached to subchondral bone - limited capacity for repair (nourishment comes from synovial fluid) Articular capsule: Thick sac of connective tissue that covers the entire joint and provides additional joint stability Synovial membrane: thin membrane with lots of villi superficially lined by a continuous layer of specialized cells (synoviocytes – type A are phagocytic; type B produce synovial fluid) Synovial fluid: clear, viscous, colorless or slightly yellow fluid produced by synoviocytes (low cellularity and low protein content); function is to reduce friction; increases in many joint diseases (effusion)  Terms to Know: Cartilage and Ligaments Hyaline, Elastic and Fibrocartilage Ligament vs Tendon Endochondral ossification Mesenchyme Chrondroblast Perichondrium Isogenous group Growth plate components (zone of reserve/resting cells, zone of proliferation, zone of hypertrophic cells, primary spongiosa) Metaphysis, physis, epiphysis Proteoglycans Tendinocyte/Tendon Fascicle Type I vs Type II collagen Synarthroses, Cartilaginous, and Synovial Joints Type A cell and Type B cell (synoviocytes) Synovial fluid