CRP

Clinically

Unwell / irritable

Fever

Not feeding

Unable to weight bear / limp

Knee pain

Examination

Fever

Limited / painful ROM

Hip held flexed and externally rotated

- maximises volume of capsule

Lab tests

WCC > 12 000

ESR > 40

CRP > 10

Blood cultures

Incidence

Knee > Hip

- superficial position

- limited cover of well vascularised muscle 

- watershed area of skin blood supply anterior to the skin incision 

- much increased in fully constrained prosthesis 

Ideal < 1%

Risk Factors

Increased with

- revision

- prior infection

- RA / Psoriatic arthropathy

- DM

Aetiology

Intrinsic

Infection

Loosening

Thigh pain in uncemented

- micro motion at distal end of stem

- modulus mismatch

Stress fracture / insufficiency fracture

- pubic rami, sacral

Intra-operative fracture

Prosthesis failure

Subtle instability

Extrinsic