Investigation

 

THR AspirationInfected THR progressive bone loss and lysis

 

Incidence

 

Dale et al Acta Orthop 2012

- Nordic Arthroplasty Registry of 430,000 THA

- revision for infection 0.7%

 

Risk factors

- obesity

- diabetes

- rheumatoid arthritis

- biologics

- revision THA

 

Symptoms

 

Pain

Wound drainage

 

Hip infection

 

Microbiology

 

Gram positive cocci 70%

- Staph aureus

- coagulase negative Staph Epidermidis

- Streptococcus < 10%

- Enteroccus - more common acute infection

 

Aerobic gram negative bacilli 10%

- more common acute infection

 

Culture negative 6%

 

Fungus / Candida < 1%

- revision / immunosuppression

 

Pathology

 

Glycocalyx / Biofilm

- slime layer of polysaccharides produced by bacteria 

- protective barrier against antimicrobial and host defense

 

X-ray

 

1. Progressive radiolucent lines / rapid lysis

2. Focal osteolysis with endosteal scalloping

3. Periosteal new bone 

- pathognomonic of infection

- usually at junction meta / diaphysis on medial side

- uncommon

 

Infected THR progressive bone loss and lysisInfected THR Endosteal ScallopingInfected THR Periosteal New Bone

 

Infected THAInfected acetab

Femoral stem lysis                              Acetabular lysis

 

MRI / CT

 

MRI THA infectedMRI THA infected

MRI demonstrating large fluid collection around THA

 

CT THA infectedCT THA infected

CT demonstrating large fluid collection around THA

 

Diagnosis

 

Parvizi et al J Arthroplasty 2018

- any major criteria indicates infection

- minor criteria

- score 6 or greater infected

- score 4 or 5 inconclusive

- score 3 or less not infected

- 98% sensitive

Major criteria Minor criteria
Sinus tract communicating with prosthesis

Serum

- CRP > 10  (2 points)

- ESR > 30 (1 point)

- D-dimer > 860 ng/ml (2 points)

 

Identical pathogen identified on two cultures

Synovial fluid

- PMN > 80% (2 points)

- WCC > 3000 cells uL (3 points)

- synovial CRP > 6.9 mg/L (1 point)

- positive alpha-defensin (3 points)

- positive leukocyte esterase (3 points)

 

Blood tests

 

ESR > 30 - Takes 6 to 12 months to normalize post OT

CRP > 10 - takes 3 weeks to normalize post surgery

 

Austin et al J Arthroplasty 2008

- 116 patients with infection and 180 without

- normal ESR and CRP - 96% sensitivity for excluding infection

- elevated ESR and CRP - 56% sensitivity for diagnosing infection

 

Nuclear Medicine

 

1. Three Phase Bone Scan

- low specificity for infection

- normal study likely excludes infection

- Cemented THA - majority return to normal by 1 year but 10% can remain positive past 1 year

- Uncemented THA - can remain positive for 2 years or longer

- infection - increased blood flow / blood pool / delayed phase

 

THR Bone Scan NormalTHR Hot Cup Quiscent Femur

Quiescent bone scan

 

Infection blood flowBone scan infection

Infected THA on blood flow and blood pool

 

Infected bone scanInfected bone scan

Infected THA on delayed phase

 

Indium 111 Labelled White cell scan + bone scan

 

Teller et al CORR 2000

- 64% sensitive and 78% specific for diagnosis THA infection

 

PET scan / [18F]Fluoro-2-deoxyglucose positron emission tomography (FDG-PET)

 

Kwee et al Eur J Nucl Med Mol Imaging 2008

- meta-analysis 11 studies and 600 patients

- 82% sensitive and 87% specific

 

Fluid Aspiration

 

THR Aspiration

 

Cell count

 

Cipriano et al JBJS Am 2012

- WCC > 3450 uL3 91% sensitive and 93% specific

- neutrophil > 78% was 95% sensitive and 87% specific

 

Leukocyte esterase (neutrophil enzyme)

 

Parvizi et al JBJS Am 2011

- 81% sensitivity and 100% specificity

 

Culture

 

Ali et al J Arthroplasty 2006

- sensitivity 82% and specificity 91%

 

Tissue specimens

 

Intra-operative gram stain - low sensitivity

Intra-operative swabs - less sensitivity than tissue specimens

 

Fresh frozen section

- > 5 neutrophils per high-powered field

- in at least 5 separate microscopic fields

 

Bori et al Mod Pathol 2011

- sensitivity of the interface membrane 83%, specificity was 98%

- sensitivity pseudocapsule 42%, specificity was 98%

 

Tissue culture

 

Gold standard

- same microbe on two different samples

- multiple specimens best to avoid contaminants (5 - 6)

- PCR can increase diagnosis

 

Sonification

 

Using ultrasound to remove and culture biofilm from removed prostheses

- more accurate than intra-operative tissue specimens

- especially in setting of pre-operative antibiotics

 

Trampuz et al NEJM 2007

- tissue specimen: sensitivity 61% and specificity 99%

- sonificate-fluid: sensitivity 79% and specificity 99%

- 14 cases of PJI were detected by sonicate-fluid culture but not by prosthetic-tissue culture

- patients receiving antimicrobial therapy within 14 days before surgery

- sensitivities of periprosthetic tissue 45%

- sensitivity of sonicate-fluid culture 75%