BLOCK 14 HISTOLOGY OF THE JOINTS Dr N NAVSA DEPARTMENT OF ANATOMY R4-12 BMW nnavsa@med.up.ac.za

Joint Categories Traditionally – joints (arthroses / articulations) are divided into 2 categories based on: Type of material used Type of movement allowed Two categories are: Synarthroses (non-synovial joints) Diarthroses (synovial joints)

Synarthroses The material used to connect the bony elements in synarthrodial joints is interosseous connective tissue (fibrous & cartilagenous) Synarthroses are thus grouped into 2 divisions according to the type of connectives tissue

Diarthroses The ends of the bony components are free to move in relation to one another because no cartilaginous tissue directly connects adjacent bony surfaces. The bony components are indirectly connected to one another by means of a joint capsule that encloses the joint Synovial joints also have accessory structures – cartilaginous discs, plates/menisci, labrums, fat pads, ligaments, tendons, etc.

CLASSIFICATION OF JOINTS Fibrous joints Cartilagenous joints Synovial joints

Fibrous Joints Synarthroses Immobile Syndesmosis e.g. tibiofibular Suturae e.g. skull Gomphosis e.g. tooth Synostosis – bones joined by fibrous tissue

FIBROUS JOINTS

Cartilagenous joints Amphiarthroses Restricted movement Symphyseal joints Pubic symphysis : bony elements covered by hyaline cartilage with fibrous cartilage in between Intervertebral discs Specialised symphysis – hyaline cartilage plates of vertebral bodies joined by ring of fibrous cartilage e.g. annulus fibrosus

CARTILAGINOUS JOINTS

Synovial Joints Diarthroses Mobile Articular surfaces covered by hyaline cartilage Fibrous capsule lined by synovial membrane Fibrous layer (layers of collagen) of capsule connected to periosteum of bones Synovial cavity with synovial fluid Ligaments formed by irregular connective tissue Menisci / articular discs of fibrous cartilage

Synovial Joints contd Synovial membrane: Inner surface smooth / with folds (villi) Contains blood vessels, lymphatic vessels, nerves Cells about 1-6 layers on the inside Type A cells: macrophages Type B cells: fibroblasts which form synovial fluid

SYNOVIAL JOINTS

HUMAN DEVELOPMENT TEXTBOOKS Medical Embryology by J Langman 4th edn Chapter 9 : Skeletal system p123 Chapter 10 : Muscular system p138 The Developing Human by KL Moore 4th edn Chapter 15 : The skeletal system p334 Chapter 16 : The muscular system p350

NORMAL DEVELOPMENT

SKELETAL SYSTEM 3rd wk Mesoderm – series of blocks = somites Differentiation Sclerotome = ventromedial Dermatome = dorsolateral 4th wk-sclerotome cells mesenchyme=conn tissue Migration

SKELETAL SYSTEM Sclerotome cells migrate Bone formationMesenchyme Fibroblasts (matrix formation) Chondroblasts (cartilage formation) Osteoblasts (bone formation) Bone formationMesenchyme Bone can also form in somatic mesoderm of body wall

LIMBS 5th wk – limb buds Initially – mesenchyme core surr by ecto Apex of bud thickened=ectodermal ridge Ridge influences underlying mesenchyme Rapid growth & differentiation 6th wk – terminal end of buds flat = hand and foot plates

LIMBS Tissue disappearance in radial grooves = fingers & toes External shape is established 6th wk – hyaline cartilage model End of embryonic period endochondral ossification 12th wk – primary ossification centers

LIMBS Ossification progresses from primary center To the ends At birth Diaphysis completely ossified Epiphyses cartilaginous Cartilage plate inbetween = epiphyseal plate Latter NB for growth in length Full length – plate disappears, epiphyses unite

Clinical application Fracture vs Normal development Determination of proper maturation age Hand and wrists commonly used to determine “bone age”

HUMAN DEVELOPMENT ABNORMALITIES

LIMB ABNORMALITIES Amelia – 1 or 2 extremities are absent Meromelia – hands & feet attached to trunk Micromelia – all extremities present but abnormally short Polydactyly – extra fingers or toes Syndactyly – abnormal fusion Lobster claw – abn cleft betw 2nd & 4th metacarpal (MC) bones & sift tissues; 3rd MC & phalanges almost always absent; thumb, index finger, 4th, 5th finger may be fused. Club foot – sole in, foot add & plantar flexed