BLOCK 14 HISTOLOGY OF THE JOINTS

Dr N NAVSADEPARTMENT OF ANATOMY

R4-12 BMWnnavsa@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 DEVELOPMENTTEXTBOOKS

• 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– Fibroblasts (matrix formation)– Chondroblasts (cartilage formation)– Osteoblasts (bone formation)

• Bone formationMesenchyme • 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