Cartilage and Joints - University of Nottingham

Cartilage and Joints Learning Outcomes By the end of this lecture students should be able to: Describe the features and function of different joint types and give examples Describe in detail the structure of a synovial joint Provide details of the properties of individual elements of a syn...

Cartilage and Joints Learning Outcomes By the end of this lecture students should be able to: Describe the features and function of different joint types and give examples Describe in detail the structure of a synovial joint Provide details of the properties of individual elements of a synovial joint (e.g. the knee joint) Describe some of the accessory structures about a synovial joint e.g. ligaments, bursae BIOS3100: Musculoskeletal Physiology Dr John Harris (Oct ’24)  Joint Classification By Function When bones (or bone and cartilage) come together they form a JOINT (a.k.a. an ARTICULATION) Function a balance between movement and stability Classification according to function: Synarthrosis or immobile joint – joint held firmly together to give protection and stability with no permitted movement Amphiarthrosis – joint providing protection and stability, with some limited movement Diarthrosis – freely moveable joint allowing extensive movement of body (axial skeleton) and limbs (appendicular skeleton)  Joint Types By Structure Three joint types according to structure: Fibrous – joints held firmly together by fibrous connective tissue Cartilaginous – bones firmly held together by hyaline cartilage or fibrocartilage Synovial – bones not directly joined (fluid- filled joint cavity); nature of contacting bone surfaces allows smooth movement between the bones Fibrous and cartilaginous joints can be synarthrosis or amphiarthrosis joints All synovial joints are diarthrosis joints  Fibrous Joints Bones directly connected by fibrous tissue with no joint cavity Gap between bones can vary from narrow to wide depending on length of fibres. Three types of fibrous joint: - Sutures - Gomphoses - Syndesmoses Fibrous Joints: Sutures Strongly bind bones of skull Narrow, synarthrotic joints Protection of brain Helps to form the face Begin as wider areas of connective tissue in newborn = fontanelles Some sutures ossify causing skull bones to fuse = a synostosis Fibrous Joints: Gomphoses A gomphosis is a narrow joint between a tooth root (so not bone) and its jaw ‘socket’ (alveoli) a.k.a. peg-and-socket joint Anchored by short dense connective tissue bands = periodontal ligament Immobile therefore a synarthrosis Fibrous Joints: Syndesmoses A syndesmosis is where two parallel bones are joined together e.g. tibia and fibula - narrower joints joined by ligaments (fibrous band) - wider joints by interosseous membrane (broad fibrous sheet) Prevents separation of bones Amphiarthrosis as not all movement prevented (but very little) - gives stability and weight- bearing support  Cartilage Reminder Connective tissue made up of cells plus extracellular matrix ECM = protein fibres + ground substance Ground substance = water + large organic molecules Cartilage comprised of dense network of collagen or elastic fibres embedded in proteoglycans (containing e.g. chondroitin sulphate, keratan sulphate, hyaluronic acid) and water Precursor cartilage cells = chondroblasts. Mature chondrocytes located in lacunae Collagen fibres provide strength; chondroitin resilience (rubbery)  Elastic Cartilage Surface of most cartilage surrounded by membrane, perichondrium (composed of collagen fibres) Chondrocytes are located within elastic fibres in the extracellular matrix Provides strength and elasticity hence supports the shape of certain structures e.g. external ear  Fibrocartilage Chondrocytes scattered within bundles of collagen fibres in the extracellular matrix (no perichondrium) Strongest form - provides support and joins certain structures together e.g. intervertebral discs, menisci of knee  Hyaline Cartilage Many chondrocytes within fine collagen fibres in the extracellular matrix Provides support, flexibility and smooth surface for joint movement, but weakest form (no perichondrium over articular cartilage or epiphyseal plate) e.g. ends of long bones  Cartilaginous Joints Two forms of cartilaginous joint: ○ A synchondrosis ‒ Bones joined by hyaline cartilage OR a bone joined to hyaline cartilage ○ A symphysis ‒ Bones joined by fibrocartilage (but bone can have hyaline cartilage on its end) ‒ Fibrocartilage contains numerous bundles of thick collagen fibres → greater ability to resist pulling and bending forces compared to hyaline cartilage  Cartilaginous Joints: Synchondrosis Region of hyaline e.g. Epiphyseal growth plate cartilage joining diaphysis and epiphysis of long bone When growth ends, plate becomes bone (synostosis) Immobile therefore synarthrotic joint Can be considered a temporary synchondrosis  Cartilaginous Joints: Symphysis Intervertebral discs e.g. Intervertebral symphysis comprised of outer ring of fibrocartilage Soft, pulpy highly elastic interior → cushioning effect Allow small movements between adjacent vertebrae (amphiarthrotic) Across entire vertebral column large range of movement Synovial Joints Most common joint type Articular capsule joins articulating bones creating joint (synovial) cavity Capsule comprises two layers: ‒ Outer fibrous membrane (of mostly collagen) ‒ Inner synovial membrane (synovium) Synovial Joints 2 Surfaces of contacting bones covered in thin smooth layer of articular (hyaline) cartilage Filled with lubricating synovial fluid – viscous fluid that reduces friction Affords significant joint mobility (diarthrotic) and helps to avoid shock but less stable than other joints  Subchondral Bone e.g. the knee joint Cartilage is avascular, aneural and has no lymphatic system If damaged, no capacity to regenerate new cartilage Subchondral bone (e.g. in femur/tibia) connected to cartilage via calcified layer Vascularised but exchange with chondrocytes dependent on diffusion – limits thickness of cartilage  The Synovial Membrane Synovial membrane (synovium) comprised of connective tissue, collagen fibres and adipose tissue (articular fat pads) Synoviocytes responsible for secretion of synovial fluid (synovia) which forms a thin film over structures in joint cavity In addition to lubrication, this fluid also provides nourishment to the articular cartilage Synovial Fluid Viscous clear or pale yellow, sterile fluid in healthy joint Consists of high levels of hyaluronic acid, lubricin and associated glycoproteins The fluid component is an ultrafiltrate of plasma (transudate) from capillaries in the synovium Normal synovial fluid also contains some (< 100/ml) leucocytes (mainly monocytes)  Menisci e.g. the knee joint Some synovial joints have fibrocartilage pads between the articulating bones Attached to the fibrous capsule Two forms: ‒ An articular disc is generally small and oval-shaped ‒ A meniscus is larger and C-shaped. Each meniscus in knee joint provides cushioning (as can fat pads) and shock absorption between the bones  Ligaments Ligaments = strong bands of e.g. the knee joint fibrous connective tissue Accessory ligaments located outside (medial and lateral collateral ligaments) and inside (anterior and posterior cruciate ligaments) the articular capsule Strengthen and support the joint by anchoring the bones together and preventing their separation. Allow normal movements but limit the range Additional support by muscles/tendons acting across joint  Bursa(e) A bursa is thin connective tissue sac filled with lubricating liquid located outside of a synovial joint Prevent friction between the bones of the joint and the overlying muscle, tendons or skin A tendon sheath is similar to a bursa but smaller Surrounds a tendon where it crosses a joint to permit smooth movement of the tendon when muscle contracts and joint moves  Some Further Reading Muscolino, J.E. (2017) Kinesiology: the skeletal system and muscle function, 3rd Edition, Elsevier, Chapter 7: Classification of Joints Young, B., O’Dowd, G. & Woodford, P. (2014) Wheater’s Functional Histology: A Text and Colour Atlas, 6th Edition, Elsevier/Churchill-Livingstone, Chapter 10 Skeletal Tissues Tortora, G.J. & Derrickson, B.H. (2009) Principles of Anatomy and Physiology, 12th Edition, Wiley, Chapter 7: Joints