Geriatric MedicineTier 1Disease (DEADMAN)

Arthritis - septic arthritis

Description

Bacterial invasion of a joint space - orthopaedic emergency, esp in older adults where diagnosis is often delayed
Native joint or prosthetic joint infection (PJI) - different organisms, thresholds, management
Elderly often present without classic fever/severe pain - low threshold required

Incidence rises with age; higher in RA, prosthetic joints, diabetes, immunosuppression
Knee > hip most commonly affected native joint
PJI: ~1-2% of arthroplasties, higher in revision surgery

Staph aureus - commonest overall, incl. MRSA
Streptococci - second commonest
Gram-negatives - more frequent in elderly, urinary source, immunosuppressed
Route: haematogenous (bacteraemia seeding, esp. in polyarticular disease) > contiguous spread > direct inoculation (joint injection, trauma, surgery)
PJI: early (<3 months, intraoperative contamination, virulent organisms) vs delayed (3-24 months, indolent, coagulase-negative staph/Cutibacterium) vs late (>24 months, haematogenous)

Clinical

Hot, swollen, painful joint with reduced range of movement
- Elderly may present atypically - low-grade fever, confusion, functional decline, minimal pain
Always ask re: recent bacteraemia source, joint injection, skin breach

Investigations

Joint aspiration before antibiotics if at all possible - synovial WCC, gram stain, culture, crystals (exclude gout/pseudogout mimicry, though can coexist)
- Synovial WCC >50,000/uL (native) supports septic; lower thresholds apply for PJI
Blood cultures x2 - positive in ~50%
Inflammatory markers (CRP/ESR) - trend, not diagnostic alone
Imaging - plain film baseline, MRI if osteomyelitis/deep collection suspected; for PJI, imaging + serial synovial fluid + intraoperative cultures per orthopaedic protocol

Native joint

Urgent orthopaedic referral - surgical washout/drainage (arthroscopic or open) + antibiotics
Empirical IV antibiotics after cultures taken - cover Staph aureus (incl. MRSA risk factors), adjust to culture
Duration - typically 2-4 weeks IV/oral depending on organism and response, per local guideline

Prosthetic joint infection

MDT with orthopaedics + ID
Early PJI: consider debridement, antibiotics, implant retention (DAIR)
Delayed/chronic: usually one- or two-stage revision - implant removal required for cure in most
Prolonged targeted antibiotics (often months) +/- suppressive therapy if not surgical candidate

Supportive

Delayed diagnosis -> irreversible cartilage destruction within days
Mortality inc with age, comorbidity, delayed treatment
Native joint: risk of permanent joint damage, chronic pain, reduced function
PJI: risk of recurrent infection, need for repeat surgery, amputation in refractory cases (rare)

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