growth plate dysfunctions

all zones

Diastrophic dwarfism

· defect in type II collagen synthesis

Pseudoachondroplastic dwarfism

· abnormal accumulation of layers in rER of chondrocytes

Kneist syndrome

· defective processing of proteoglycans

Hurler’s syndrome

· inborn error of metabolism

· accumulation of mucopolysaccharides chondroitin sulphate and heparitin sulphate in chondrocytes

Morquio’s syndrome

· inborn error of metabolism

· accumulation of mucopolysaccharide keratosulphate in swollen chondrocytes (foam cells)

Cretinism

· thyroid deficiency

· abnormal mucopolysaccharide metabloism

· chondroitin sulphate accumulation in chondrocyte

Reserve zone

· no specific abnormality

proliferative zone

· abnormalities may affect

· chondrocyte proliferation

· matrix production

Achondroplasia

· germ plasm defect

· enchondral bone formation inhibited

· membranous bone formation normal

· defect in proliferative zone

· chondrocyte proliferation decreased

· columns poorly formed

· subsequent narrowing of hypertrophic zone

· scanty metaphyseal bone formation

· periosteal strip of fibrous tissue from perichondrium may seal growth plate

· leads to decreased longitudinal growth and short bones

· shaft diameter normal

· subperiosteal membranous bone formation normal

· metaphysis flared

· due to continued latitudinal growth

Malnutrition

· decreases chondrocyte production in proliferative zone

· chondrogenesis slowed

· bone formation in metaphysis continues until metaphyseal seal foms

· resulting dense line called growth arrest line or Harris line

Irradiation

· affects proliferative zone primarily

· decreases chondrocyte proliferation

· does not affect latitudinal bone growth

· similar bones to achondroplasia

Hormones

Sex hormones

· oestrogen excess depresses chondroblastic proliferation

· testosterone excess increases chondroblastic proliferation

· complex interaction as may cause premature plate closure

Glucocorticoid excess

· depresses chondroblastic proliferation

Growth hormone excess

· increases chondroblastic proliferation

· also stimulates membranous ossification

· causes gigantism

Growth hormone deficiency

· opposite effect

· produces proportionate dwarf

hypertrophic zone

Multiple enchondromatosis

· cartilage may be immature hypertrophic cells

· may also originate from cambium layer

Rickets

· calcifiable matrix formed

· matrix does not calcify

· primary spongiosa not formed

· hypertrophic zone greatly widened and viable

· no calcified cartilage bars

· primary spongiosa not formed

· metaphysis consists of large osteoid seams surrounding thin bony trabeculae

· tongues of hypertrophic cells extend into metaphysis

Hypophosphatasia

· inborn error of ALP metabolism

· matrix fails to calcify

· hypertrophic zone widened

· similar appearance to rickets

metaphysis

· can involve

· vascular invasion

· ossification

· remodelling

Osteomyelitis

· abscess starts here

· may result in partial or total destruction of physis

· may result in stimulation of growth

Injury

· fracture usually through hypertrophic zone

Salter-Harris I & II

· blood supply to plate disrupted

· increase in width of hypertrophic zone

· with healing, vascular supply reestablished

· plate becomes normal

Salter-Harris III, IV & V

· growth stops if healing of epiphysis to metaphysis occurs

Scurvy

· two effects

1. defect in chondroitin sulphate production in proliferative zone

2. deficiency in collagen formation

· primarily affects metaphysis

· calcified cartilage accumulates at bone-cartilage junction

· bony trabeculae sparse and thin

Osteogenesis imperfecta

· collagen does not mature beyond reticulin fibre stage

· is disease of osteoblasts

· primarily affects metaphysis

· formation of secondary spongiosa deficient

Osteopetrosis

· internal remodelling deficient

· calcified cartilage bars of primary spongiosa not resorbed

· primitive bone laid down

· no medullary cavity produced