BONES

Normal skeletal system Bone is a type of connective tissue Inorganic component – calcuim

hydroxyapatite Organic component – cells & protein

of matrix

Bone forming cells – osteoprogenitor cells, osteoblasts & osteocytes

Osteoblasts – uninucleate, along new bone forming surfaces, synthesise bone matrix

Osteoblasts surrounded by matrix - osteocytes

Osteocytes – numerous, osteoblasts which get incorporated into bone matrix during synthesis, found within lacunae

Osteoclasts – large multinucleate cells, bone resorption

Osteiod matrix – 90-95% of type I collagen

Osteoblasts depositing collagen in random weave – woven bone / orderly layered – lamellar bone

Cartilage lacks blood vessels, lymphatics & nerves

2 components – cartilage matrix & chondrocytes

Cartilage matrix – inorganic – hydroxyapatite

Organic – 80% water, 20% type II collagen & proteoglycans

Chondrocytes – primitive mesenchymal cells – chondroblasts -> chondrocytes

Hyaline cartilage, fibrocartilage, elastic cartilage

INFECTIONS – OSTEOMYELITIS Inflammation of bone & marrow Manifests as primary solitary focus

of disease Systemic diseases spreading to bone

– typhoid, actinomycosis, syphilis, brucellosis, mycetoma

* Pyogenic bacteria & mycobacteria

PYOGENIC OSTEOMYELITIS Bacterial infection – hematogenous

route , contiguous site , direct implantation

Infants & young children – 5-15 yrs Long bones / vertebral bodies Common – staph aureus- express

receptor to bone matrix components & facilitates adherence to bone tissue

E.coli, Pseudomonas, Klebsiella Location – neonate-> metaphysis Children – metaphysis Adult – epiphysis

Morphology – Depends on stage – acute , subacute

or chronic & location of infection Suppuration, ischaemic necrosis,

healing by fibrosis & bony repair Acute inflammatory reaction -> cell

death Entrapped bone – necrosis Bacteria & inflammation spreads

Infection begins in metaphyseal end of marrow cavity occupied by pus, microscopy shows congestion, oedema, & exudate of neutrophils

Infection spreads along marrow cavity to endosteum, haversial canal – Periosteitis

May reach subperiosteal space – subperiosteal abscess

May penetrate through cortex creating draining sinus tracts

Combination of suppuration & impaired blood supply to cortex results in erosion, thinning & infarction necrosis of cortex – Sequestrum

Later there is formation of new bone beneath periosteum present over infected bone. This forms encasing sheath around necrosed bone - Involucrum

Continued neo-osteogenesis gives rise to dense sclerotic pattern of osteomyelitis

Occasionally acute osteomyelitis may be contained to a localised area & walled off by fibrous tissue & granulation tissue – Brodie’s abscess

Clinical course – Acute systemic illness with malaise ,

fever, chills , leucocytosis & pain X – ray – lytic focus of bone

destruction surrounded by zone of sclerosis

Blood culture , biopsy

Complications Septicaemia Acute bacterial arthritis Pathologic # SCC Secondary amyloidosis

TUBERCULOUS OSTEOMYELITIS Adolescents or young adults Morphology – Blood borne , originate from focus of

active infection Sites – spine , knees & hips

Central caseous necrosis, granuloma Involvement of joint space &

interverebral disc are frequent Pott’s disease – TB of spine

commences in vertebral body, may be associated with compression #, destruction of intervertebral discs -> permanent damage & paraplegia

Psoas abscess – extension of caseous material alongwith pus from lumbar vertebrae to sheaths of psoas muscle

Pain on motion , localized tenderness , fever,chills & weight loss

Kyphosis & scoliotic deformities Neurologic deficits