Prosthetic Joint Infection

Prosthetic joint infection is microbial infection involving a joint prosthesis and surrounding tissues.

It differs fundamentally from native septic arthritis because bacteria adhere to implant surfaces and develop biofilm, dramatically reducing antimicrobial susceptibility and protecting organisms from host immune clearance.

Definitive cure usually requires a combined surgical and antimicrobial strategy.

Common organisms include:

• Staphylococcus aureus
• Coagulase negative staphylococci
• Streptococci
• Enterococci
• Gram negative bacilli
• Cutibacterium acnes, particularly shoulder arthroplasty

Polymicrobial infection is more common with severe soft tissue compromise and early postoperative wound contamination.

Classification by timing and pathogenesis

A practical classification is:

Early postoperative infection

Develops within approximately 4 weeks of arthroplasty.

Usually acquired during surgery.

Typical presentation:

• Persistent wound drainage
• Increasing pain
• Erythema
• Effusion
• Fever

Late acute haematogenous infection

Occurs in a previously well functioning prosthesis after bacteraemic seeding.

Symptoms begin suddenly, often years after arthroplasty.

Common sources include:

• Skin infection
• Endocarditis
• Urinary infection
• Dental infection
• Respiratory infection

Chronic PJI

Symptoms have generally been present for more than several weeks, often with mature biofilm, implant loosening, sinus formation or progressive bone loss.

DAIR has substantially poorer eradication rates in established chronic infection.

Tsukayama classification

Type I

Positive intraoperative cultures at presumed aseptic revision.

Type II

Early postoperative infection.

Type III

Acute haematogenous infection.

Type IV

Late chronic infection.

This remains useful conceptually because the infection mechanism directly influences whether implant retention is realistic.

2018 diagnostic criteria

PJI is confirmed by either major criterion:

• Two cultures positive for the same microorganism

or

• Sinus tract communicating with the prosthesis

A weighted diagnostic system can then incorporate:

• Serum CRP above approximately 10 mg/L
• ESR above 30 mm/hour
• Synovial WBC above approximately 3,000 cells/µL in chronic hip or knee PJI
• Synovial PMN above approximately 80%
• Positive alpha defensin
• Synovial CRP
• Histology
• Purulence
• Intraoperative cultures

A preoperative score of 6 or greater strongly supports infection. Thresholds must be interpreted differently in the immediate postoperative period and in inflammatory or crystal arthropathy.

Presentation varies dramatically.

Acute infection can produce:

• Severe joint pain
• Effusion
• Erythema
• Fever
• Wound drainage

Chronic infection often presents with:

• Persistent pain
• Progressive stiffness
• Implant loosening
• Recurrent effusion
• Intermittent wound drainage
• Sinus tract

A draining sinus communicating with the prosthesis is diagnostic of infection regardless of ESR or CRP.

Pain developing in a previously well functioning arthroplasty after a bacteraemic illness should raise concern for acute haematogenous PJI.

Obtain:

• Full blood count
• CRP
• ESR

Plain radiographs assess:

• Implant position
• Radiolucent lines
• Migration
• Osteolysis
• Periprosthetic fracture

Normal radiographs do not exclude infection.

Joint aspiration

Aspirate the joint before antibiotics in a stable patient.

Send for:

• Synovial WBC
• PMN percentage
• Gram stain
• Aerobic and anaerobic culture

Consider:

• Alpha defensin
• Leukocyte esterase

according to diagnostic uncertainty.

Hold antibiotics until cultures are obtained when the patient is stable and not septic.

Surgery samples

At revision surgery, take multiple separate deep tissue cultures using separate sterile instruments.

Avoid superficial swabs.

Culture incubation may need to be prolonged for slow growing organisms such as C. acnes.

Sonication of removed implants can increase microbiological yield in selected cases.

Treatment is determined by:

• Infection duration
• Implant fixation
• Soft tissue condition
• Organism
• Biofilm maturity
• Bone loss
• Host health

DAIR

DAIR means:

Debridement, antibiotics and implant retention.

It is most appropriate when:

• Prosthesis is well fixed
• Components are well positioned and functioning
• Soft tissues permit primary closure
• No sinus tract exists
• Infection is acute

Current practical windows include:

• Early postoperative infection within approximately 4 weeks

or

• Late acute infection with symptoms for less than approximately 3 weeks

Earlier intervention gives a better chance of eradication.

At surgery:

• Perform aggressive synovectomy and debridement
• Remove necrotic tissue
• Irrigate thoroughly
• Exchange all accessible modular components, such as polyethylene liner or femoral head
• Retain only well fixed major components

Failing to exchange modular components leaves a substantial biofilm burden.

DAIR is poor treatment for:

• Loose implant
• Chronic infection
• Sinus tract
• Major soft tissue deficiency
• Infection present for several weeks with established biofilm

In these settings, exchange arthroplasty is usually preferable.

One stage exchange

Remove all components and cement, perform radical debridement and implant the definitive new prosthesis during the same operation.

Best candidates have:

• Known susceptible organism
• Good soft tissue envelope
• Limited bone loss
• No uncontrolled sinus or major abscess
• Patient physiologically suitable for definitive reconstruction

Advantages include:

• One major operation
• Faster rehabilitation
• No interval spacer morbidity

Avoid one stage revision when:

• Organism is unknown or highly resistant
• Soft tissues are severely compromised
• Massive bone loss exists
• Infection control cannot be confidently achieved during one procedure

Two stage exchange

Historically the reference strategy for chronic difficult PJI.

Stage 1

• Remove all implants
• Remove cement
• Radical debridement
• Obtain cultures
• Insert antibiotic loaded spacer where appropriate
• Culture directed antimicrobial therapy

Stage 2

After clinical and laboratory evidence supports infection control:

• Remove spacer
• Repeat debridement and cultures
• Reimplant definitive prosthesis

Spacers may be:

• Static
• Articulating

An articulating knee or hip spacer can maintain length, movement and soft tissue tension but is unsuitable in some massive bone defects or major instability.

Salvage options

When reconstruction is not feasible:

• Resection arthroplasty
• Arthrodesis
• Permanent antibiotic spacer
• Chronic antibiotic suppression
• Amputation, rarely

Antimicrobial treatment

Empirical therapy after cultures in a significantly ill patient may use:

Vancomycin IV

plus a broad Gram negative agent such as:

Cefepime 2 g IV every 8 to 12 hours

or

Piperacillin tazobactam 4.5 g IV every 8 hours by extended infusion

according to renal function and local resistance patterns.

Narrow promptly when cultures return.

Staphylococcal retained implant infection

For a susceptible staphylococcal PJI treated with DAIR, combine an active antistaphylococcal drug with rifampicin once:

• Adequate debridement has occurred
• Bacteraemia is controlled
• Wound is stable without ongoing major drainage

A commonly used rifampicin dose is:

Rifampicin 300 to 450 mg orally twice daily.

Never use rifampicin alone because resistance develops rapidly.

For MSSA, the companion initial therapy can include:

Cefazolin 2 g IV every 8 hours.

For MRSA:

Vancomycin IV with AUC guided dosing.

Rifampicin has extensive drug interactions and can reduce levels of:

• Warfarin
• Direct oral anticoagulants
• Many anticonvulsants
• Some antiretrovirals
• Multiple cardiovascular drugs

Check interactions before prescribing.

Duration

When prosthesis is retained after DAIR, approximately 12 weeks of active antimicrobial treatment remains a strong practical reference because 6 weeks has produced higher failure rates, particularly in retained implant infection.

After complete implant removal and exchange, approximately 6 weeks may be sufficient in many appropriately debrided cases, although duration must be individualised according to organism, bone involvement and reconstructive strategy.

Chronic suppressive therapy

Consider indefinite oral suppression when:

• Implant cannot be removed
• Curative surgery is prohibitively risky
• Infection is clinically controlled but not eradicated
• Organism has a suitable safe oral suppressive drug

This is suppression rather than cure.

Major causes of failure are:

• Wrong surgical strategy for infection chronicity
• Retained loose components
• Missed sinus or abscess
• Inadequate debridement
• Failure to exchange modular components during DAIR
• Resistant organism
• Major immunocompromise
• Poor soft tissue coverage