Treats established infection | Source control comes first | Staph is the main target | Biofilm needs rifampicin | Route matters less than once thought
ANTIBIOTIC THERAPY BY SETTING
Critical Must-Knows
- Treatment, not prophylaxis: this topic is about clearing established bone and joint infection - the antibiotic is an adjunct to surgical source control, never a substitute for it
- Staphylococcus aureus is the single commonest pathogen in osteomyelitis, septic arthritis, and implant infection, so empirical cover must always include it
- Biofilm on dead bone and implants shields bacteria from antibiotics and the immune system, which is why implants often must be removed and why rifampicin is added for susceptible staphylococcal implant infection
- Take cultures before antibiotics wherever it is safe to do so - blind early antibiotics can render deep cultures negative and make targeted therapy impossible
- Route is secondary to source control: oral therapy is non-inferior to intravenous therapy for many bone and joint infections once the patient is stable (OVIVA)
Clinical Pearls
- "Always distinguish prophylaxis (prevent infection in clean tissue) from treatment (eradicate established infection) - they are examined as different things
- "Never give rifampicin as a single agent - resistance emerges rapidly, so it is always combined with a partner drug
- "Choose agents with good bone penetration: clindamycin, fluoroquinolones, rifampicin, fusidic acid and linezolid penetrate bone well
- "Debridement of dead, infected bone is the most important step - antibiotics cannot sterilise a sequestrum or a biofilm-coated implant
Clinical Imaging
The radiographs of bone and joint infection
Critical Antibiotic-in-Infection Exam Points
Cultures Before Antibiotics
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.
Source Control First
Antibiotics are an adjunct to surgery, not a replacement. Pus must be drained, dead bone (a sequestrum) excised, and an infected implant debrided or removed. An antibiotic cannot penetrate a sequestrum or a mature biofilm.
Biofilm and Rifampicin
Bacteria on implants form a biofilm that resists antibiotics and immune cells. For susceptible staphylococcal implant infection, add rifampicin to a partner drug - it penetrates biofilm and kills slow-growing organisms. Never use rifampicin alone (rapid resistance).
Bone Penetration
Choose agents that reach bone: clindamycin, fluoroquinolones, rifampicin, fusidic acid and linezolid penetrate well. Glycopeptides such as vancomycin penetrate less well, which matters when oral switch or deep cure is the goal.
Memory aids
CLEANEDPrinciples of Treating Bone and Joint Infection
| C | Cultures first Deep and blood cultures before antibiotics if stable |
| L | Localise the source Imaging and examination to find the focus |
| E | Excise dead bone and drain pus Surgical source control is the priority |
| A | Agent that reaches bone Pick antibiotics with good bone penetration |
| N | Narrow to the culture De-escalate from empirical to targeted therapy |
| E | Enough duration A defined course, commonly around 6 weeks for osteomyelitis |
| D | Decide on the implant Retain with rifampicin, or remove if biofilm cannot be cleared |
| C | Cultures first Deep and blood cultures before antibiotics if stable | A | Agent that reaches bone Pick antibiotics with good bone penetration | D | Decide on the implant Retain with rifampicin, or remove if biofilm cannot be cleared |
| L | Localise the source Imaging and examination to find the focus | N | Narrow to the culture De-escalate from empirical to targeted therapy | ||
| E | Excise dead bone and drain pus Surgical source control is the priority | E | Enough duration A defined course, commonly around 6 weeks for osteomyelitis |
Hook:Get the bone CLEANED - cultures, localise, excise, agent, narrow, enough, decide on the implant.
CFR-LFAntibiotics with Good Bone Penetration
| C | Clindamycin Good bone levels, covers staph and anaerobes |
| F | Fluoroquinolones Ciprofloxacin and levofloxacin, the rifampicin partners |
| R | Rifampicin Penetrates biofilm - never used alone |
| L | Linezolid Oral, active against MRSA, watch marrow suppression |
| F | Fusidic acid Anti-staphylococcal, used as a combination partner |
| C | Clindamycin Good bone levels, covers staph and anaerobes | L | Linezolid Oral, active against MRSA, watch marrow suppression |
| F | Fluoroquinolones Ciprofloxacin and levofloxacin, the rifampicin partners | F | Fusidic acid Anti-staphylococcal, used as a combination partner |
| R | Rifampicin Penetrates biofilm - never used alone |
Hook:CFR-LF reach bone: Clindamycin, Fluoroquinolones, Rifampicin, Linezolid, Fusidic acid.
LONGWhen an Implant Cannot Be Saved
| L | Loose implant Loosening means the implant must come out |
| O | Old infection Long symptom duration favours removal over retention |
| N | No biofilm-active drug usable Resistant organism or rifampicin not tolerated |
| G | Grossly unwell or sinus tract Sinus or systemic sepsis points to removal |
| L | Loose implant Loosening means the implant must come out | N | No biofilm-active drug usable Resistant organism or rifampicin not tolerated |
| O | Old infection Long symptom duration favours removal over retention | G | Grossly unwell or sinus tract Sinus or systemic sepsis points to removal |
Hook:A LONG, loose, old, untreatable, septic implant comes out rather than being retained.
Overview
This topic is about using antibiotics to treat established orthopaedic infection - osteomyelitis, septic arthritis, and prosthetic joint or other implant infection. It is the opposite side of the coin to surgical prophylaxis: prophylaxis prevents infection in clean tissue before contamination, whereas here the infection is already present and the goal is to eradicate it.
Three ideas run through everything that follows and 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.
Principles: How Antibiotics Work in Bone Infection
To clear a bone or joint infection an antibiotic has to do three things: 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:
- Poor blood supply: 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: bacteria on implant surfaces and dead bone secrete a protective matrix. Inside it they grow slowly and tolerate antibiotic concentrations many times higher than would kill free-floating bacteria.
- Intracellular survival: Staphylococcus aureus can survive inside osteoblasts and other cells, providing a reservoir that ordinary antibiotics reach poorly.
Bone penetration of common agents:
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 |
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 that would easily 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.
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). The classic indication is a stable, susceptible staphylococcal implant infection of short duration that is being managed with debridement and implant retention (DAIR).
Clinical Pearl
Rifampicin is the "biofilm" answer in the viva, but two qualifiers must always come with it: it is only added once a partner drug is established and the wound is dry (to avoid selecting resistance), and 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.
Clinical Relevance
Antibiotic therapy for infection touches every part of orthopaedic practice and the exam. In trauma, early antibiotics plus debridement halve the early infection rate after open fractures. In arthroplasty, prosthetic joint infection is a feared complication, and the decision to retain (with rifampicin) or remove the implant 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 principles apply: culture, source control, the right drug into bone, narrow to the organism, and a defined duration.
Antibiotic Therapy by Clinical Scenario
Acute (including haematogenous) osteomyelitis
Commonest organism: 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.
Principles:
- Take blood cultures and, where feasible, a bone aspirate or biopsy before antibiotics.
- Start empirical anti-staphylococcal therapy (for example flucloxacillin for MSSA; add 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 is 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.
Evidence Base
Oral Is Non-Inferior to IV for Bone and Joint Infection (OVIVA)
- 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
Rifampicin Combination Cures Staph Implant Infection (FBI Study, Zimmerli)
- 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
Antibiotics Roughly Halve Early Open-Fracture Infection (Cochrane Review)
- 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
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Principles of Treating Osteomyelitis (~3 min)
"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."
Framework: Chronic osteomyelitis is a surgical disease in which antibiotics are an adjunct. I would aim to identify the organism, achieve surgical source control, then give a targeted antibiotic course.
Diagnosis and cultures: I would take deep operative tissue samples for culture and histology - sinus swabs are unreliable and I would not rely on them. Where the patient is stable I would withhold antibiotics until deep samples are taken, so cultures are not falsely negative.
Source control: The key step is surgical debridement - excision of all dead, infected bone, including any sequestrum, plus management of the resulting dead space and soft tissues. No antibiotic can sterilise dead bone.
Antibiotics: I would start empirical anti-staphylococcal cover and then narrow to the culture, choosing an agent with good bone penetration. A typical total course is around six weeks, individualised to the organism, the surgery, and the response in symptoms and inflammatory markers. Oral therapy is a reasonable route once the patient is stable, supported by the OVIVA trial.
Infected Hip Replacement and the Rifampicin Question (~4 min)
"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?"
Recognition: This is an acute prosthetic joint infection. With an early presentation, a stable well-fixed implant and healthy soft tissues, the implant may be salvageable.
Samples first: I would take blood cultures and, in theatre, multiple separate deep tissue samples before antibiotics, so I can confirm the organism and its sensitivities. In a stable patient I would not give blind antibiotics beforehand.
Source control: The appropriate operation is debridement, antibiotics and implant retention - a thorough washout and debridement with exchange of modular components, keeping the fixed implant.
Antibiotics and rifampicin: I would start targeted therapy against the cultured organism. If this is a susceptible staphylococcus, once the wound is dry and a partner drug such as a fluoroquinolone is established, I would add rifampicin for its biofilm activity. Rifampicin is never given alone because resistance emerges rapidly. The Zimmerli foreign-body infection trial showed that a ciprofloxacin-rifampicin combination cured stable staphylococcal implant infections without removal.
If retention fails or the implant is loose: I would move to revision surgery - one-stage or two-stage - because a biofilm-coated, loose implant cannot be cleared in situ.
ANTIBIOTICS IN ORTHOPAEDIC INFECTION
Clinical summary
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
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.