septic arthritis

Introduction

septic arthritis is one of those diagnoses you do not want to miss
delay in diagnosis may cause joint damage as well as life threatening sepsis / septicaemia
unfortunately, many other conditions cause a hot, swollen joint, and some with associated fevers
- are you sure it is not a bursitis or overlying cellulitis with no joint involvement?
- full range of movement of the joint with minimal pain in a normal patient makes it unlikely to be infected
joint infections are generally from penetrating injuries, haematogenous spread, post-operative, or spread from local osteomyelitis
investigation and management is different for native vs prosthetic joint infections (PJI)
for children, see RCH guideline - osteomyelitis and septic arthritis

IV access
take bloods for FBE, U&E, CRP, ESR, urate, blood cultures x 2
Xray joint to exclude fracture
- later changes include:
  - narrow joint space if > 1 week
  - subchondral osteoporosis
  - end-stage bone destruction
if hip joint, consider USS
discuss with orthopaedic team early
- ?role of joint aspiration
  - essential for knee, elbow or gleno-humeral joint
  - joint aspirate suggesting septic:
    - WCC > 50 000/mm^3 (usually > 100 000/mm^3)
    - Neutrophil usually > 75%
    - Glucose < BSL
    - Protein levels increased - usually 6-8g/dL
    - ± Crystals as acid pH decreases solubility
    - bacteria seen in 30%
    - 60% are culture positive
- ?delay antibiotics if no severe sepsis until after surgery
- consider Te99 Scan
  - helps differentiate osteomyelitis

surgical infection “early PJI”
- these present within 3 months of implantation
delayed or late PJI
- these present after 3 months of implantation (3-24 months = delayed; > 24 months = late)
haematogenous spread PJI:
- usually occur after 24 months of implantation

at least one of the following:
- ≥2 cultures of synovial aspirate or tissue cultures of intraoperative specimens yields the same microorganism
- Purulence surrounding the prosthesis is observed during reoperation
- Presence of sinus tract
- Histopathological findings consistent with acute infection

IV access
take bloods for FBE, U&E, CRP, ESR, blood cultures x 2
Xray joint to exclude fracture and to look for loosening
If the patient is not systemically unwell (signs of severe sepsis / septicaemia), HOLD OFF giving antibiotics until after 1st surgical debridement
If severe sepsis, then consult with orthopaedic team and consider starting (also consider ID consult if starting antibiotics):
- vancomycin, plus
- ceftriaxone
contact ortho team for admission
- patients with haematogenous or early PJI may be candidates debridement and retention of the prosthesis IF there is no loosening AND symptom duration < 3 weeks
- other patients are likely to be managed with resection +/- reimplantation
- multiple intraoperative tissue samples (>3 and ≤5) should be obtained for microbiological examination.
- post-operatively patients are usually discharged on 6-12 months oral antibiotics followed by longer term review at 18-24 months