Infection

· commonest cause of failure

incidence

· ideal incidence is < 1%

· actual incidence ranges from 1% to 5%

· increased with

· revision procedure

· prior knee infection

· rheumatoid arthritis

· diabetes

classification

Early

· within 3 months of operation

· due to contamination during surgery

· usually easy to diagnose

· persistent fever and swelling

· wound discharge

· elevated ESR

· aspiration performed if diagnosis in doubt

Late

· more than 3 months after operation

· usually due to haematogenous spread

· sources include

· teeth

· skin lesions

· urinary tract

· may also be due to operative contamination and dormant organism

· may be difficult to diagnose

· presents as pain

· difficult to distinguish from mechanical cause

· aspiration indicated

prevention

Prophylactic antibiotics

· should be used

· perioperatively

· before dental and urinary procedures

· antibiotics should be administered promptly to treat remote infection

· eg. chest, skin, urinary

Environment

· laminar flow theatre

· minimisation of theatre traffic

Technique

· meticulous handling of tissues

· avoidance of haematoma

treatment

Reimplantation

Indications

· late infection

· loose prosthesis

· patient able to tolerate multiple procedures

Technique

· first stage

· prosthesis and cement removed completely

· cement spacer may be inserted

· IV antibiotics for 6 weeks

· clinical and laboratory assessment of resolution of infection

· pain, redness, swelling, discharge

· ESR and CRP

· reaspiration

· second stage

· when felt that infection resolved

· Gram stain and frozen section

· abort procedure if positive

Results

· successful in 80%

Debridement

Indications

· early infection

· late infection in securely fixed and well-functioning prosthesis

Technique

· incision, drainage and debridement

· copious irrigation

· primary skin closure

· suction drainage not indicated

· administration of antibiotics

· depending on sensitivities

· duration of 4 weeks

Results

· successful in only 30%

· increased success with

· early infection

· early debridement once infection present

· low virulence organism

Antibiotic suppression

Indications

· prosthesis removal not feasible

· anaesthetic contraindication

· low virulence organism

· susceptibility to oral antibiotic

· minimal toxicity from antibiotic

· prosthesis not loose

Results

· uncommonly indicated

· successful in 30%

Resection arthroplasty

Indications

· polyarticular RA

· low ambulatory demands

Advantages

· easier to sit than with arthrodesis

Disadvantages

· unstable

· may be painful to walk

Technique

· prosthesis and all cement removed

· temporary fixation of bone ends with pins or sutures

· alternative is cement spacer

· plaster for 6 months

· weight bearing as tolerated

Results

· successful in 70%

· wound healed without infection

· functional ambulation in 50%

· usually with brace or walking aid

Arthrodesis

Indications

· single joint disease

· young age

· high functional demand

· deficient extensor mechanism

· poor soft tissue coverage

· immunocompromised patient

· highly virulent organism requiring toxic therapy

Contraindications

· bilateral knee disease

· ipsilateral hip or ankle disease

· severe segmental bone loss

· contralateral amputation

Advantages

· high success rate at eradicating infection

Disadvantages

· loss of knee motion

· shortening

Technique

· original incision should be used

· all foreign material should be removed

· may require multiple debridements

· most important prerequisite is vascular cancellous bone apposition

· bone resection should be minimal

· can use TKR jigs

· aim for horizontal tibial cut with posterior slope for desired flexion

· femoral cut made to provide up to 5^o valgus

· alignment straight for IM nail

· severe bone loss should be supplemented with cancellous graft

· should have negative culture before bone grafting

· optiumum position relates to clearance

· 10-20^o flexion with minimum bone loss

· extension with significant bone loss

External fixation

· advantages

· adjustable

· allows access to soft tissues

· no longstanding foreign body

· needs little additional soft tissue dissection

· suitable for active infection

· disadvantages

· nonrigid

· potential neurovascular injury

· pinsite problems

· requires removal

· decreased union rate

· optimum configuration is combination of

· biplanar fixation with 6 medial-lateral pins

· uniplanar fixation with 4 anterior pins

· fixation maintained until clinical union achieved

· usually 12 weeks

· plaster cylinder applied until radiological union achieved

· usually 4-12 weeks

Intramedullary nail

· advantages

· high union rate

· no pinsite problems

· disadvantages

· unsuitable for active infection (intramedullary spread)

· retained foreign body

· requires careful planning to determine length and diameter of nail

· tibia reamed antegrade and femur reamed retrograde

Results

· union rate

· 70% with external fixator

· 90% with IM nail

Amputation

Indications

· life-threatening infection

· local infection with massive bone loss

· immunocompromised patient with systemic sepsis

Frequency

· performed in 5%