Prosthetic knee infection

Prosthetic knne joint infections are classified as early,those occurring within 3 months of implantation, and delayed delayed, 3–12 months after implantation and late, more than 12 months after implantation.

Early and delayed infections are usually due to organisms introduced at the time of surgery.

Late infections are more likely to be hematogenously acquired.

Infecting organisms form microcolonies on the prosthesis surface.

Infectious organisms elaborate polysaccharides that coalesce, forming a biofilm that resists host immne responses and reduces susceptibility to antibiotics as a result of changes in metabolic processes and poor diffusion.

Early infections may present with a leaking wound or the acute onset of fever, pain, swelling, effusion and erythema at the implant site.

Untreated infections may form chronic sinuses.

Bacteremia and a systemic infections may occur.

Late infections may present with joint pain, restriction of movement, and sinus development may occur.

Radiological loosening may be suggestive of infection.

Late infections occasionally present with an acutely inflamed joint that may be associated with sepsis.

Risk factors for prosthetic joint infection include previous joint arthroplasty, a surgical site infection, the presence of malignancy, advanced age, diabetes mellitus, previous native joint infection, obesity, poor nutrition, skin disease, and pre-existing joint disease, especially rheumatoid arthritis.

Patients with a history of a revision of an existing prosthetic joint are at greater risk than those undergoing primary joint replacement.

Post-operative surgical site infection may be indicative of deeper infection involving the implant.

Hematogenous seeding of a bacteremic infection to a prosthesis is rare event accounting for less than 0.5% of cases.

Staphyloccoccal aureus bacteremia may seed a prosthetic joint with significant frequency, and are the most frequently isolated organism from early, delayed and late infections.

Coagulase negative staphylococcus accounts for most of these (30%–41%) with S. aureus as the second most common (12%–39%).

Late infections are presumed to be of hematogenous etiology and S. aureus seems to predominate at this point, but coagulase negative staphylococcus may still account for a third of cases.

Streptococci, enterococci and diphtheroids each account for around 10% of cases.

Gram-negative organisms are much less common than Gram-positive, causing around 8% of cases.

Resistant organisms are still relatively uncommon and the majority of resistant and polymicrobial infections occur within the first 3 months following arthroplasty.

CRP of less than 13.5 mg/L had a negative predictive value of 88.5% in the diagnosis of late prosthetic knee infection.

A CRP above this had a positive predictive value of only 59.2%.

Normal CRP results do not exclude infection and abnormal results may reflect pathology elsewhere.

Plain X-rays of the affected joint is unhelpful in early infection.

Chronic infection may cause bone loss and evidence of loosening around an implant but these changes are not specific to infection.

Ultrasound may demonstrate effusions or synovial thickening and if joints are amenable to aspiration or biopsy

MRI is not generally of value due to metal artefact.

If an acute infection is suspected blood cultures and a joint aspirate should be taken before antibiotics are administered.

One should not delay the timely administration of antibiotics if severe systemic sepsis is present.

A peri-prosthetic biopsy under fluoroscopy is an alternative and may increase the chances of sampling the area with the highest density of organisms in chronic infections.

Multiple arthroscopic synovial biopsies may be useful in the diagnosis of chronic prosthetic knee infection.

The diagnosis of infection is made by a combination of clinical, histological and biopsy or intra-operative microbiological criteria.

Surgical samples or aspirates are more likely to be culture-negative if the patient has received any antibiotics in the preceding 3 months.

Antibiotics should be withheld until all diagnostic microbiological tests have been completed.

When a joint is revised, multiple intra-operative specimens should be taken?

It is recommended that microbiology specimens are cultured for at least 5 days.

Certain organisms, such as Propionibacterium spp. and Corynebacterium spp. require longer incubation periods.

Effective treatment requires a combination of an appropriate surgery with, in most cases, suitable antibiotic therapy.

In some patients surgical cure of infection may not be practical or appropriate.

Options for management include: no surgery with or without antibiotic suppression, amputation, joint fusion or removal, prosthesis retention with debridement and antibiotics, and joint revision in either one or two stages.

Some patients, especially with multiple co-morbidities, or in whom a curative procedure is likely to be technically challenging, may be best managed conservatively; may be by long-term antibiotic suppression, acceptance of a chronically discharging sinus, or indeed deliberate formation of a sinus.

It may be inappropriate to subject an individual to a revision when, and such cases may be best managed by prosthesis removal, and in other cases repeated attempts at revision and salvage may fail to eradicate infection, and again an excision arthroplasty with removal of all foreign material may be appropriate.

Conservative surgical management involves debridement of a joint with exchange of modular components and/or liners but retaining the prosthesis itself, combined with prolonged antibiotic therapy.

Higher rates of failure when arthroscopic washout is used compared with open debridement, particularly in those cases where S. aureus is isolated.

Revision may be performed as either a one- or two-stage procedure.

A one-stage procedure involves sampling, removal of the infected joint, thorough debridement followed by re-scrubbing, re-draping and insertion of a new prosthesis.

A two-stage procedure separates sampling, joint removal, thorough debridement and closure, the first-stage, from subsequent re-insertion by weeks or months.

A cement spacer is essential for knee joints.

There are commercially available antibiotic-impregnated cements and a range of other antimicrobials can also be added to cement.

Most administer systemic antibiotics for up to 6 weeks post-operatively before insertion of a new prosthesis 2 or more months later.

The role of effective debridement at the first stage, which should include removal of all cement, cement restrictors and prosthetic material is essential.

Two-stage revisions are the most widely favored.

One-stage revision may be appropriate for selected cases.

One Stage revision may be appropriate for those too frail to withstand two procedures and the demanding rehabilitation that follows a long period of relative immobility.

One-stage revision may not be advisable for those with resistant or difficult-to-treat organisms.

Antibiotics can be delivered systemically or locally to the joint, usually through the use of loaded cement.

Antibiotic administration should be guided by local organism susceptibilities and must be active against staphylococci and a wide range of nosocomial multiresistant Gram-negative organisms.

Some physicians rely on local antibiotics alone, suggesting there is no additional benefit from the co-administration of systemic therapy.

The widely accepted practice is to give empirical systemic antibiotics after the first-stage operation while awaiting culture results.

Specific antibiotic therapy is then given for up to 6 weeks, usually intravenously but orally if an agent of suitable oral bioavailability is available.

Failure of inflammatory markers or clinical signs of infection to settle during this time raises the possibility of persistent infection and re-debridement is essential.

An antibiotic-free period of around 2 weeks may be considered following completion of therapy prior to the re-implantation second stage.

Empirical antibiotics are given peri-operatively and stopped if cultures are negative.

The significance of positive cultures from samples taken at re-implantation is not clear, as positive microbiological sampling of the joint space at the second stage did not predict outcome, although the majority of such patients did receive further antibiotics.

The optimum duration of antibiotic treatment following a one-stage revision is not known and reports range from 1 week to several months, with outcomes similar to those with two-stage revisions, most likely reflecting that a thorough and extensive debridement is the most critical predictor of success.

When systemic antibiotics are used there is no clear evidence to support oral or an intravenous route.

Daptomycin with activity against MRSA, glycopeptide-intermediate S. aureus and glycopeptide-resistant enterococci, demonstrates an efficacy equivalent to that of vancomycin and it demonstrates synergy with rifampicin against vancomycin-resistant enterococci and MRSA.

Evidence supporting any specific antibiotic regimen for the treatment of Gram-negative joint infection is lacking.

Around 7%–11% of prosthetic joint infections confirmed by histology are culture-negative.

Agents should be selected on the basis of the clinical history, the presence of resistant organisms (for example MRSA colonization) and any previously positive samples. Empirical treatment with a glycopeptide and/or cephalosporin may be as effective as specific therapy in those cases in which the organism is known.15

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The high infection rates associated with prosthetic joint implantation in the 1970s have fallen dramatically as a result of improvements in patient selection and preparation, surgical technique, theatre design, prophylactic antibiotics and anaesthesia. The introduction in 2005 of the UK Department of Health’s ‘Saving Lives’ delivery programme for acute hospitals was designed to help organizations to reduce healthcare-associated infections. This programme now includes a care bundle aimed at the prevention of surgical site infection.65 MRSA screening and decolonization is now mandatory for all elective orthopaedic admissions in the UK.66

There has been controversy over the role of dental prophylaxis for patients with joint replacements. There is no evidence that dental procedures are a risk factor for prosthesis infection, nor that prophylaxis impacts infection rates.67 Therefore prophylactic antibiotics prior to dental procedures in patients with prosthetic joints should not be recommended.

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