Basic Science · Infection

Orthopaedic Antibiotic Therapy

This topic is about TREATING established bone and joint infection — osteomyelitis, septic arthritis, and prosthetic joint/implant infection — which is the opposite of surgical prophylaxis (prevention in clean tissue). The dominant principle is that antibiotics are an ADJUNCT to surgical source control, never a substitute: pus must be drained, dead bone (a sequestrum) excised, and an infected implant debrided or removed, because no drug penetrates a sequestrum or a mature biofilm. STAPHYLOCOCCUS AUREUS is the single commonest organism across osteomyelitis, septic arthritis and implant infection, so empirical cover must include it (then narrow to culture). Take DEEP cultures (and blood cultures) BEFORE antibiotics whenever the patient is stable — blind early antibiotics can render deep cultures negative and forfeit targeted therapy (the exception is sepsis). BIOFILM on implants and dead bone is the central concept in implant infection: it shields slow-growing bacteria from antibiotics and the immune system, which is why implants often must be removed and why RIFAMPICIN — which penetrates biofilm — is added for susceptible staphylococcal implant infection, ALWAYS with a partner drug (a fluoroquinolone), never alone (resistance emerges rapidly), in the setting of a stable, early infection managed by debridement and implant retention (DAIR). Choose agents that reach bone (clindamycin, fluoroquinolones, rifampicin, fusidic acid, linezolid penetrate well; vancomycin less so). Route is secondary once stable — oral is non-inferior to IV (OVIVA) — and a typical osteomyelitis course is around 6 weeks (shorter, ~2–4 weeks, for a washed-out septic joint).

S. aureusCommonest organism — always cover empirically

BiofilmWhy implants resist clearance — add rifampicin (never alone)

Source controlDrain pus, excise dead bone, debride/remove implant

Oral = IVNon-inferior once stable (OVIVA); ~6 weeks for osteomyelitis

Bottom lineTreating established bone/joint infection: antibiotics are an adjunct to surgical source control (drain pus, excise sequestrum, debride/remove implant). Cover S. aureus empirically; take deep cultures BEFORE antibiotics (except in sepsis); use bone-penetrating agents (clindamycin, fluoroquinolones, rifampicin, linezolid, fusidic acid). Biofilm drives implant infection — add rifampicin (with a partner, never alone) for stable early susceptible staph in DAIR; remove a loose/chronic/sinus implant. Oral is non-inferior to IV once stable (OVIVA); ~6 weeks for osteomyelitis.

Overview

Three ideas run through everything that follows, and they are the threads examiners pull on. First, antibiotics are an adjunct to surgery: dead bone and infected implants must be dealt with surgically, because no drug penetrates a sequestrum or a mature biofilm. Second, the right drug means an agent that covers the likely organism, usually Staphylococcus aureus, and actually reaches bone. Third, biofilm on implants changes the rules: it is the reason implant infection is so hard to clear, the reason rifampicin is added for susceptible staphylococci, and the reason an implant sometimes has to be removed.

Where it turns up. In trauma, early antibiotics plus debridement roughly halve the early infection rate after open fractures. In arthroplasty, prosthetic joint infection is a feared complication, and the decision to retain the implant with rifampicin or remove it is a core viva. In paediatrics, acute haematogenous osteomyelitis and septic arthritis are emergencies where prompt, correctly chosen antibiotics after cultures can avoid surgery or growth disturbance; in the basic-science viva, the biofilm concept, bone penetration and the rifampicin rule are classic asks. Across all of these the same sequence applies: culture, localise the focus by examination and imaging, source control, the right drug into bone, narrow to the organism, and a defined duration.

Principles: How Antibiotics Work in Bone Infection

What the drug has to do. To clear a bone or joint infection an antibiotic has to reach the infected tissue at an adequate concentration, remain active against the organism, and keep working in the hostile environment of infected bone: low oxygen, dead tissue, biofilm.

Why bone is a difficult place to treat. Chronically infected, sclerotic bone and any dead fragment (a sequestrum) have little or no blood flow, so the drug simply cannot get there; this is the single biggest reason chronic osteomyelitis needs surgery. Biofilm, the subject of the next section, shields the bacteria on implants and dead bone. Staphylococcus aureus can also survive inside osteoblasts and other cells, a reservoir that ordinary antibiotics reach poorly.

Cultures first. Take deep cultures (and blood cultures) before starting antibiotics whenever the patient is stable. Blind early antibiotics can sterilise the surface and leave deep cultures negative, so you lose the chance to target therapy. The exception is sepsis, where you cannot delay treatment.

Which agents reach bone. Choose agents that reach bone; the table gives the penetration and usual role of each. Fusidic acid is anti-staphylococcal and is used as a combination partner rather than on its own. Glycopeptides such as vancomycin penetrate less well, which matters when oral switch or deep cure is the goal.

Clindamycin

Bone penetration: Good
Typical role in bone or joint infection: Staph and anaerobe cover, useful oral switch

Fluoroquinolones (cipro/levofloxacin)

Bone penetration: Good
Typical role in bone or joint infection: Gram-negative cover and the usual rifampicin partner

Rifampicin

Bone penetration: Good (penetrates biofilm)
Typical role in bone or joint infection: Added for susceptible staph implant infection - never alone

Linezolid / fusidic acid

Bone penetration: Good
Typical role in bone or joint infection: Oral options against resistant gram-positives

Flucloxacillin

Bone penetration: Moderate
Typical role in bone or joint infection: First-line for methicillin-susceptible S. aureus (MSSA)

Vancomycin (glycopeptide)

Bone penetration: Lower
Typical role in bone or joint infection: MRSA cover but less reliable bone levels

Bone Penetration and Role of Common Agents
Agent	Bone penetration	Typical role in bone or joint infection
Clindamycin	Good	Staph and anaerobe cover, useful oral switch
Fluoroquinolones (cipro/levofloxacin)	Good	Gram-negative cover and the usual rifampicin partner
Rifampicin	Good (penetrates biofilm)	Added for susceptible staph implant infection - never alone
Linezolid / fusidic acid	Good	Oral options against resistant gram-positives
Flucloxacillin	Moderate	First-line for methicillin-susceptible S. aureus (MSSA)
Vancomycin (glycopeptide)	Lower	MRSA cover but less reliable bone levels

Adverse effects and interactions of a prolonged orthopaedic course

Bone and joint infection means weeks of antibiotics, so the safety and interaction profile is examinable in its own right:

Rifampicin is a potent hepatic enzyme (cytochrome P450) inducer: it lowers the effect of warfarin, the oral contraceptive pill (counsel on alternative contraception) and many other drugs, can be hepatotoxic, and turns secretions orange, staining tears and contact lenses.
Fluoroquinolones, the rifampicin partner, cause tendinopathy and tendon rupture, classically the Achilles, especially in the elderly, in renal impairment or with concurrent steroids, plus QT prolongation and CNS effects.
Linezolid causes reversible myelosuppression (especially thrombocytopenia) beyond about two weeks, peripheral and optic neuropathy with prolonged use, and is a monoamine-oxidase inhibitor, so there is a serotonin syndrome risk with SSRIs.
Aminoglycosides (gentamicin) are nephrotoxic and ototoxic, relevant both systemically and from high-dose local elution; vancomycin is nephrotoxic and needs therapeutic level monitoring; clindamycin is the classic cause of Clostridioides difficile colitis.
A prolonged course, often outpatient (OPAT), therefore needs monitoring of the full blood count, renal and liver function, and drug levels.

What Imaging Shows

Plain radiographs. Chronic osteomyelitis leaves its vocabulary on the film: osteolysis, sequestrum, involucrum and periosteal new bone. The sequestrum is dead bone with no blood supply, which is why antibiotics alone will not clear it. Chronic low-grade infection thickens bone; a tumour usually destroys it.

Anteroposterior radiograph of a left wrist with mottled lucency and sclerosis of the distal radius in chronic osteomyelitis — Chronic osteomyelitis on a plain film: an anteroposterior view of a left wrist (marker L) with mottled lucency and sclerosis through the distal radial metaphysis.Credit: Eplasty — PMC (NIH) open access (CC BY)

Anteroposterior radiograph of a left femur with a yellow arrow at the distal diaphysis, where the cortex is thickened and sclerotic — Anteroposterior radiograph of a left femur (marker L), the yellow arrow at the distal diaphysis where the cortex is thickened and sclerotic.Credit: Cureus — PMC (NIH) open access (cc by)

MRI. MRI is what separates marrow oedema from a collection that needs draining. An abscess is T2 hyperintense and T1 hypointense; in the hindfoot this is Brodie's abscess territory.

Two MRI panels of the same femur: a long-axis T1 view (A) with hypointense marrow, an orange arrow at abnormal intramedullary signal and a 29 cm scale bar, and an axial T2 view (B) with an arrow at the bright abscess cavity in the medullary canal — The same femur on MRI. Panel A is a long-axis T1 view, the marrow hypointense, with the orange arrow on abnormal intramedullary signal and a scale bar to 29 cm; panel B is an axial T2 view in which the arrow marks the bright abscess cavity within the medullary canal, the collection that needs draining.Credit: Cureus — PMC (NIH) open access (cc by)

Three MRI panels of the calcaneus labelled A to C, with white arrows on a posteromedial lesion that is bright in A and dark in B, and blue and white arrows on the axial view in C — A posteromedial calcaneal abscess in three MRI panels: bright under the arrow in A, dark in B, and marked by blue and white arrows on the axial view in C.Credit: Journal of the Belgian Society of Radiology — PMC (NIH) open access (cc by)

Nuclear medicine. The bone scan is sensitive and indiscriminate; the labelled white cells are what localise infection.

Three rows of nuclear-medicine images of diabetic feet with previous toe amputations, labelled A bone scan, B leucocyte scan and C CXCR4 PET/CT, planar on the left and fused on the right, with red and blue arrows at the same two sites on each row — Three studies of the same diabetic feet, with previous toe amputations, labelled row by row: bone scan (A), leucocyte scan (B) and CXCR4 PET/CT (C), planar images on the left and fused images on the right, with red and blue arrows marking the same two sites on every row. Compare how much of each foot lights up on the bone scan with how little does on the leucocyte scan.Credit: European journal of nuclear medicine and molecular imaging — PMC (NIH) open access (cc by)

The diabetic foot. Bone visible or palpable at the base of an ulcer makes osteomyelitis likely before any scan is ordered.

Four foot radiographs: the upper pair carries red arrows at osteolysis of the fifth metatarsal head and adjacent phalanx, and the lower pair is labelled L — Diabetic foot osteomyelitis: in the upper pair of radiographs the red arrows mark osteolysis of the fifth metatarsal head extending into the phalanx; a second pair of views, labelled L, sits below.Credit: Cureus — PMC (NIH) open access (cc by)

Biofilm and the Role of Rifampicin

Biofilm is the central concept in implant-associated infection. Within hours of contamination, bacteria attach to the implant surface and to dead bone and begin to secrete an extracellular matrix. The bacteria inside this biofilm are metabolically slow, physically shielded from antibiotics and immune cells, and can tolerate drug concentrations many times higher than would kill the same organism floating free. This is why a biofilm-coated implant usually cannot be sterilised by antibiotics alone and often has to be removed.

Schematic of biofilm forming on an implant surface: planktonic bacteria attach, build an extracellular matrix dome, shielding slow-growing bacteria from antibiotics and immune cells, with rifampicin penetrating. — The schematic, left to right as labelled: planktonic bacteria attach to the implant surface, multiply, and are enclosed in an extracellular matrix (biofilm) that blocks antibiotics and immune cells while the bacteria inside grow slowly, shielded. The green dotted track at the right edge is rifampicin penetrating the biofilm.Credit: OrthoVellum schematic diagram

Rifampicin is special because it penetrates biofilm and kills slow-growing, adherent staphylococci that other drugs miss. The catch is that staphylococci develop resistance to rifampicin very quickly if it is used on its own, so it is always combined with a partner drug, commonly a fluoroquinolone such as ciprofloxacin or levofloxacin, and it is only added once the partner drug is established and the wound is dry, to avoid selecting resistance.

When it is worth using. The classic indication is a stable, susceptible staphylococcal implant infection of short duration that is being managed with debridement and implant retention (DAIR). Rifampicin is the biofilm answer in the viva, but it is only worth using when the implant is stable and the infection is caught early; a loose implant or long-standing infection usually needs removal, not rifampicin.

Schematic of staphylococcal biofilm formation labelled primary attachment phase (A Aap, B MSCRAMM) and accumulation phase (C Aap/SasG B domain-mediated, D MSCRAMM-mediated) — Staphylococcal biofilm assembly as the source draws it: a primary attachment phase to the surface through cell-wall-anchored proteins (A, Aap; B, MSCRAMM), then an accumulation phase in which the cells link to one another (C, Aap/SasG B-domain-mediated; D, MSCRAMM-mediated). The accumulated community is what rifampicin is added to reach.Credit: Frontiers in cellular and infection microbiology — PMC (NIH) open access (CC BY)

Scanning electron micrographs of bacterial biofilm on coated Ti6Al4V, uncoated Ti6Al4V and glass at two magnifications, with 5 µm and 2 µm scale bars — Biofilm under the scanning electron microscope on three substrates, labelled coated Ti6Al4V, Ti6Al4V and glass, at two magnifications (scale bars 5 µm above, 2 µm below). The implant surface is not a passive bystander; it is the substrate.Credit: Journal of materials science. Materials in medicine — PMC (NIH) open access (cc by)

Local delivery. Systemic antibiotics are only half the story in implant and bone infection; local delivery achieves very high concentrations at the site with low systemic levels. Antibiotic powder mixed into polymethylmethacrylate (PMMA) bone cement is used as beads or chains, a cement mantle, or an articulating or static spacer in two-stage revision, and it elutes a high early burst then a long low-level tail.

What can go into cement. The cement polymerises with an exothermic reaction, so only heat-stable, powdered antibiotics can be used: gentamicin, tobramycin and vancomycin are the standard choices, and liquid or heat-labile agents are unsuitable. High antibiotic loading weakens the cement, so heavily loaded high-dose cement is used for spacers and beads (infection control) rather than for load-bearing structural fixation.

Carriers that stay and carriers that go. PMMA is non-absorbable: it is itself a foreign body that can host biofilm and usually has to be removed. Biodegradable carriers that do not need removal are the alternatives:

Calcium sulphate beads
Gentamicin-collagen sponges
Bioactive glass

Two-stage revision. The infected implant is removed and replaced with an antibiotic spacer; after an interval of systemic antibiotics and confirmed clearance, the definitive implant is reimplanted.

Three panels of serial radiographs of a right femur: a locked intramedullary nail (a), a nail with a cluster of bead-like densities beside the distal femur (b), and the femur with all metalwork removed (c) — An infected nonunion managed with a custom antibiotic-coated nail, on serial films of a right femur (marker R): the original locked nail (a), the antibiotic-coated nail with a cluster of bead-like densities beside the distal femur (b), and the femur with the metalwork out (c). Local delivery puts the drug where the blood supply cannot.Credit: Healthcare (Basel, Switzerland) — PMC (NIH) open access (cc by)

Antibiotic Therapy by Clinical Scenario

The organism. In acute, including haematogenous, osteomyelitis the commonest organism is Staphylococcus aureus. In specific groups think wider: Salmonella and other gram-negatives in sickle cell disease, group B streptococcus and gram-negatives in neonates, Kingella kingae in young children.

The sequence. Take blood cultures and, where feasible, a bone aspirate or biopsy before antibiotics. Start empirical anti-staphylococcal therapy, for example flucloxacillin for MSSA, adding MRSA cover such as vancomycin where MRSA is likely, then narrow to the culture. Surgery (drainage, debridement) is needed if there is an abscess, a sequestrum, or failure to respond to antibiotics.

Duration. Commonly around 6 weeks total for osteomyelitis, individualised to the organism, the surgery performed, and the clinical and inflammatory-marker response.

Children Often Avoid Surgery

Uncomplicated acute haematogenous osteomyelitis in a child, caught early, often responds to antibiotics alone with an early switch from intravenous to oral therapy once the child improves and markers fall. Surgery is reserved for abscess, no response, or a confirmed septic joint.

Guidelines, Registries and Global Practice

Staphylococcus aureus is consistently reported as the commonest organism in osteomyelitis, septic arthritis, and prosthetic joint infection across global series, so empirical regimens everywhere are built around reliable anti-staphylococcal cover.
Local resistance patterns drive empirical choice: where MRSA prevalence is high, empirical regimens add a glycopeptide (such as vancomycin) or another MRSA-active agent until cultures return, then narrow.
The OVIVA trial has shifted international practice towards earlier oral switch for stable bone and joint infection, reducing prolonged intravenous lines and hospital stay while preserving cure rates.
The rifampicin combination for stable staphylococcal implant infection, established by the Zimmerli foreign-body infection trial, is embedded in major prosthetic-joint-infection guidance (for example IDSA and European consensus statements) as the basis for the DAIR strategy.
For open fractures, society guidance worldwide pairs early antibiotics with prompt irrigation, debridement and stabilisation, keeping antibiotic courses short and grade-appropriate rather than open-ended.

Exam Viva Scenarios

Practise clinical reasoning and management decisions out loud

Viva scenarioStandard

Principles of Treating Osteomyelitis (~3 min)

Clinical prompt

“A 40-year-old man has chronic osteomyelitis of the tibia after a previous open fracture, with a discharging sinus. The examiner asks how you would approach antibiotic treatment.”

Viva scenarioAdvanced

Infected Hip Replacement and the Rifampicin Question (~4 min)

Clinical prompt

“A 70-year-old woman develops a hot, painful hip three weeks after a primary total hip replacement. The wound is healing and the implant looks well-fixed on radiographs. How would you manage the infection and what is the role of rifampicin?”

Exam day cheat sheet

ANTIBIOTICS IN ORTHOPAEDIC INFECTION

Core Principles

Treatment of established infection - an adjunct to surgery, never a substitute
Cultures (deep and blood) before antibiotics if the patient is stable
Source control first: drain pus, excise dead bone, debride or remove implant
Narrow empirical therapy to the cultured organism

The Right Drug

Cover Staphylococcus aureus empirically (the commonest organism)
Pick agents that reach bone: clindamycin, fluoroquinolones, rifampicin, linezolid, fusidic acid
Flucloxacillin for MSSA; vancomycin for MRSA (lower bone penetration)
Rifampicin for susceptible staph implant infection - always with a partner drug

Biofilm and Implants

Biofilm shields bacteria from antibiotics and immune cells
Stable, early, susceptible implant infection: DAIR plus rifampicin combination
Loose implant, chronic infection, sinus, or resistant organism: remove the implant
Never give rifampicin alone (rapid resistance)

Duration and Route

Osteomyelitis: commonly around 6 weeks total, individualised
Septic arthritis: shorter (often 2 to 4 weeks) once the joint is washed out
Oral is non-inferior to IV for many bone/joint infections once stable (OVIVA)
Open fractures: early antibiotics plus urgent debridement, short grade-appropriate course

Evidence Base

How to read this evidence

Three trials anchor the topic: OVIVA (oral is non-inferior to IV once stable), the Zimmerli Foreign-Body Infection trial (the evidence base for rifampicin-combination DAIR in stable staphylococcal implant infection), and the Gosselin Cochrane review (early antibiotics roughly halve open-fracture infection, as an adjunct to debridement).

Evidence

Oral versus Intravenous Antibiotics for Bone and Joint Infection (OVIVA)

LoE 1

Li HK, Rombach I, Zambellas R, et al. • N Engl J Med (2019)

Key Findings:

Randomised non-inferiority trial, 1054 adults treated for bone or joint infection at 26 UK centres
Oral versus intravenous antibiotics for the first 6 weeks after surgery or starting treatment
Treatment failure at one year: 13.2 percent oral versus 14.6 percent intravenous - oral was non-inferior
Oral therapy was associated with shorter hospital stay and fewer intravenous-catheter complications

Clinical implication: For many complex bone and joint infections, a well-chosen oral antibiotic with good bone penetration is as effective as intravenous therapy once the patient is stable and source control is achieved - allowing earlier discharge and avoiding line complications.

Verify on PubMed (PMID 30699315)

Evidence

Rifampicin Combination Cures Staph Implant Infection (FBI Study, Zimmerli)

LoE 1

Zimmerli W, Widmer AF, Blatter M, Frei R, Ochsner PE • JAMA (1998)

Key Findings:

Randomised, double-blind, placebo-controlled trial in staphylococcal infection of stable orthopaedic implants
All patients had debridement and a short-duration infection, then ciprofloxacin plus rifampicin or placebo
Cure without implant removal: 100 percent (12 of 12) with rifampicin versus 58 percent (7 of 12) with placebo
Established that biofilm-active rifampicin combinations can salvage a retained implant in selected cases

Clinical implication: In a stable, early, susceptible staphylococcal implant infection managed with debridement, adding rifampicin to a fluoroquinolone allows cure with implant retention - the evidence base for the rifampicin rule in DAIR.

Verify on PubMed (PMID 9605897)

Evidence

Antibiotics Roughly Halve Early Open-Fracture Infection (Cochrane Review)

LoE 1

Gosselin RA, Roberts I, Gillespie WJ • Cochrane Database Syst Rev (2004)

Key Findings:

Systematic review pooling 913 participants across randomised and quasi-randomised trials
Antibiotics reduced early infection versus placebo or no antibiotic (relative risk 0.41)
Absolute risk reduction about 8 percent, with a number needed to treat of roughly 13
Insufficient data to judge effects on osteomyelitis, nonunion, amputation or death

Clinical implication: Level I evidence that early antibiotics are a core part of open-fracture care, halving early infection - but they work as an adjunct to prompt irrigation, debridement and stabilisation, not instead of them.

Verify on PubMed (PMID 14974035)

Bone Penetration and Role of Common Agents

Agent

Bone penetration

Typical role in bone or joint infection

Clindamycin

Good

Staph and anaerobe cover, useful oral switch

Fluoroquinolones (cipro/levofloxacin)

Good

Gram-negative cover and the usual rifampicin partner

Rifampicin

Good (penetrates biofilm)

Added for susceptible staph implant infection - never alone

Linezolid / fusidic acid

Good

Oral options against resistant gram-positives

Flucloxacillin

Moderate

First-line for methicillin-susceptible S. aureus (MSSA)

Vancomycin (glycopeptide)

Lower

MRSA cover but less reliable bone levels

Duration. Commonly around 6 weeks total for osteomyelitis, individualised to the organism, the surgery performed, and the clinical and inflammatory-marker response.

Children Often Avoid Surgery

Feature	Favours retention (DAIR + rifampicin)	Favours removal (revision)
Symptom duration	Short (acute, caught early)	Long-standing / chronic
Implant fixation	Well-fixed, stable	Loose
Organism	Susceptible, rifampicin usable	Resistant or rifampicin not tolerated
Soft tissues	Healthy, no sinus	Sinus tract, poor soft tissues

Feature	Favours retention (DAIR + rifampicin)	Favours removal (revision)
Symptom duration	Short (acute, caught early)	Long-standing / chronic
Implant fixation	Well-fixed, stable	Loose
Organism	Susceptible, rifampicin usable	Resistant or rifampicin not tolerated
Soft tissues	Healthy, no sinus	Sinus tract, poor soft tissues