Osteomyelitis: pyogenic, tuberculous and syphilitic

Lesion

Infection of bone and marrow. Bacteria kill bone, which becomes a dead fragment that antibiotics cannot reach; TB and syphilis make chronic, destructive forms.

Updated Nov 12, 2026

Key points

Organisms: S. aureus overall; group B streptococcus and E. coli in neonates; Salmonella (and S. aureus) in sickle cell disease; Pseudomonas in people who inject drugs and in foot puncture wounds; polymicrobial in diabetic feet.
Children: metaphysis of long bones (slow, looping vessels); neonates also epiphysis and joint; adults: vertebrae.
Sequestrum = dead bone fragment; involucrum = shell of new subperiosteal bone; cloaca = opening through which pus drains.
Brodie abscess: walled-off intraosseous abscess; Garré sclerosing osteomyelitis: thick reactive bone, often the jaw.
Chronic complications: pathologic fracture, secondary amyloidosis, squamous cell carcinoma in a draining sinus tract, endocarditis and sepsis.
Pott disease: tuberculous destruction of vertebral bodies and discs, gibbus deformity, paravertebral cold abscess, psoas abscess, cord compression.

What it is

Osteomyelitis is inflammation of bone and marrow, almost always from infection. Pyogenic osteomyelitis reaches bone through the blood (children, people who inject drugs, the vertebrae of older adults), from a nearby focus (diabetic foot ulcers, sinusitis, dental infection) or by direct implantation (open fractures, surgery). Staphylococcus aureus causes most cases. Mycobacterial osteomyelitis is a chronic granulomatous destruction, typically of the spine (Pott disease), and still common where tuberculosis is endemic, including Colombia. Syphilis affects bone in congenital and tertiary disease.

Structure

Acute: neutrophils fill the marrow, pus raises intraosseous pressure, vessels thrombose and bone dies.
Pus lifts the periosteum (children's periosteum is loosely attached), forming subperiosteal abscesses and depriving the cortex of blood.
Chronic: sequestrum surrounded by granulation tissue, lymphocytes and plasma cells, and an involucrum of reactive woven bone.
Tuberculous: caseating granulomas with Langhans giant cells destroying bone and crossing the disc; little reactive bone.
Congenital syphilis: osteochondritis at the growth plate and periostitis (saber shin, saddle nose); tertiary syphilis: gummas with necrosis.

Step by step

Bacteria arrive by the blood, from a contiguous focus or by direct implantation.
In children they lodge in the slow-flowing metaphyseal sinusoids; bacteria bind matrix proteins such as collagen.
Neutrophils and bacterial toxins destroy bone; pus under pressure compresses vessels and causes necrosis.
Dead bone (sequestrum) becomes a reservoir of bacteria protected in biofilm, out of reach of antibiotics and immune cells.
Reactive new bone forms an involucrum; untreated infection becomes chronic with draining sinuses.

Clinical notes

Child with fever, limp and local tenderness over a metaphysis: acute haematogenous osteomyelitis; MRI shows marrow oedema early.
In the diabetic foot, probing to bone through an ulcer strongly suggests osteomyelitis.
Chronic osteomyelitis often needs surgical removal of the sequestrum plus prolonged antibiotics.
Back pain, fever and weight loss in an area endemic for tuberculosis: consider Pott disease; it also follows HIV infection.

In the lab

Blood cultures, bone biopsy culture and histology identify the organism.
ESR and CRP rise and help follow the response to treatment.

Test yourself

Think of the answer, then tap the question to see it.

What is a sequestrum?

A fragment of dead bone in osteomyelitis that harbours bacteria and must often be removed.

Which organism is classically linked to osteomyelitis in sickle cell disease?

Salmonella, although S. aureus remains common.

Why is the metaphysis the usual site in children?

Its looping, slow-flowing vessels let blood-borne bacteria settle.

What is Pott disease?

Tuberculous osteomyelitis of the spine, destroying vertebrae and discs and causing gibbus and cold abscesses.

Which cancer can arise in a chronic draining sinus of osteomyelitis?

Squamous cell carcinoma.

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Connections

Microorganisms4

← All of general pathology

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Osteomyelitis (StatPearls (NCBI Bookshelf), 2025); Tuberculous Spondylitis (Pott Disease) (StatPearls (NCBI Bookshelf), 2025); Vertebral Osteomyelitis (StatPearls (NCBI Bookshelf), 2025).

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Representative model, for educational purposes only.