Wound, Bone and Joint Infections

Question 1

Most common causes of surgical site infections

Answer 1

Staph aureus (MSSA and MRSA) 
E.coli 
Pseudomonas aeruginosa

Question 2

Causes of surgical site infections

Answer 2

Contamination of wound at operation
Pathogenicity and innoculum of microorganisms
Host immune response

Question 3

Pathogenesis of surgical site infections

Answer 3

If surgical site is contaminated with
> 10 5 microorganisms per gram of tissue, risk of SSI is increased.
The dose of contaminating bacteria required to cause infection is much lower if there is foreign material present e.g silk suture

Question 4

Three levels of surgical site infection

Answer 4

Superficial incisional - affects skina dn subcutaneous tissue
Deep incisional - affect fascial and muscle layers
Organ/space infection - any part of anatomy other than incision

Question 5

Admitted in February 2012, with a subarachnoid and subdural haemorrhage after a fall. Decompressive craniectomy
April 2012. Cranioplasty with titanium plate.

October 2012. Admitted with large subdural collection with midline shift
16.10.12 Abscess evacuation. Titanium plates removed. Underneath there was severe infection with 1-1.5cm thick pus.

Pus grew MRSA - treatment?

Answer 5

IV linezolid

Question 6

Preventing surgical site infections (when can interventions be done)

Answer 6

Pre-operative phase:
Pre-operative showering (patients should be advised to shower or bath using soap on the day of surgery or the day before).
Nasal decontamination: S.aureus is carried int he nares of 20-30%

Intra-operative phase:
Hair removal: micro-abrasions caused by shaving with a razor may lead to multiplication of bacteria - use electric clippers on the day of surgery with single-use head. Hair should not be removed unless it will interfere with the operation.
Antibiotic prophylaxis: should be given at induction of anaesthesia. Bactericidal concentration of the drug should be established in the serum and tissues at the time of incision.
Avoid contact with infected/colonised surgical personnel.
Keep theatre with only essential personnel: microbial load in theatre is related to the number of people present.
Ventilation: maintain positive pressure ventilation, filtering all air. Keep the operating room doors closed and consider laminar flow for orthopaedic implant surgery.
Sterilisation of surgical instruments
Prepare skin prior to incision: prepare using antiseptic preparation (povidine-iodine or chlorhexidine (70% alcohol)
Aseptic and surgical technique: Maintaining effective haemostasis while preserving adequate blood supply, gently handling tissues, avoiding inadvertent entries into hollow viscus, removing devitilised tissues and eradicating dead space; Adhere to asepsis when placing intravascular devices or epidural catheters
Normothermia: mild hypothermia increases the risk of SSIs by causing vasoconstriction, decreased delivery of oxygen to wound space and subsequent impairment of neutrophil function. In theatre measure patients temperature before inducing anaesthesia and start forced air warming if temperature is below 36, use warm IV fluids and warm irrigation fluid.
Oxygenation: maintain optimal oxygenation during surgery to maintain a Hb saturation of more than 95%

Post-operative phase:
Keep wound site protected and clean
Minimise contact with people with infections
Have clean dressings and change dressings using aseptic techniquers

Question 7

Risk factors for surgical site infections

Answer 7

Age - an independent risk factor. A direct linear trend of increasing risk until 65 years of age.
Presence of remote infections at time of surgery - prevent by treating all infections remote to the surgical site prior to surgery…may require postponing of operation.
Underlying illness: ASA score >3, DM, malnutrition, low serum albumin, radiotherapy and steroids (taper steroids), RA (stop DMARDs for 4 weeks before and 8 weeks post-op)
Obesity: adipose tissue is poorly vascularised - poor oxygenation of tissues and functioning of the immune response increases the risk of SSIs.
Smoking: nicotine delays primary wound healing, peripheral vascular disease, encourage tobacco cessation.

Question 8

Management of infected/colonised surgical personnel

Answer 8

Encourage surgical personnel who have symptoms of a transmissible infection to report to occupational health.

Question 9

Bone and joint infections

Answer 9

Septic arthritis
Vertebral osteomyelitis
Chronic osteomyelitis
Prosthetic joint infection

Question 10

Risk factors for septic arthritis

Answer 10

Rheumatoid arthritis , osteoarthritis, crystal induced arthritis
Joint prosthesis
Intravenous drug abuse
Diabetes, chronic renal disease, chronic liver disease
Immunosuppression- steroids
Trauma- intra-articular injection, penetrating injury

Question 11

Pathophysiology of septic arthritis

Answer 11

Organisms adhere to the synovial membrane, bacterial proliferation in the synovial fluid with generation of host inflammatory response.
Joint damage leads to exposure of host derived proteins such as fibronectin to which bacteria adhere

Question 12

Bacterial factors causing infection in septic arthritis

Answer 12

S.aureus has receptors such as fibronectin binding protein that recognise selected host proteins.
Kingella kingae synovial adherence is via bacterial pili

Some strains of Staph. aureus produce the cytotoxin PVL ( Panton-Valentine Leucocidin) which have been associated with fulminant infections.

Question 13

Host factors causing infection in septic arthritis

Answer 13

Leucocyte derived proteases and cytokines can lead to cartilage degradation and bone loss.
Raised intra-articular pressure can hamper capillary blood flow and lead to cartilage and bone ischaemia and necrosis.
Genetic deletion of macrophage –derived cytokines (lymphotoxin alpha, TNFalpha, interleukin 1 receptor) reduces host response in S.aureus sepsis in animal models
Absence of interleukin10 in knockout mice increases the severity of staphylococcal joint disease.
Genetic variation in expression of these cytokines may lead to differential susceptibility to septic arthritis.

Question 14

Causative organisms in septic arthritis

Answer 14

Staph aureus -46%
Streptococci: pyogenes, pneumoniae, agalactiae
Gram negative: e.coli, haemophilus influenzae, neisseria gonorrhoea, salmonella
Coagulate negative staphylococci -4%
Rare: lyme, brucellosis, mycobacteria, fungi

Question 15

Clinical features of septic arthritis

Answer 15

1-2 week history of red, painful, swollen restricted joint
Monoarticular in 90%
Knee is involved in 50%

Patients with rheumatoid arthritis may show more subtle signs of joint infection

Question 16

Investigations in septic arthritis

Answer 16

Blood culture before antibiotics are given

Synovial fluid aspiration for microscopy and culture
ESR,CRP
-Traditionally a synovial count> 50,000 WBC cells/mm3 used to suggest septic arthritis
(Negative culture result does not exclude septic arthritis)

Question 17

Imaging used in septic arthritis

Answer 17

US- confirm effusion and guide needle aspiration
CT- erosive bone change, periarticular soft tissue extension
MRI- joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis

Question 18

Management of septic arthritis

Answer 18

Antibiotics: up to 6 weeks of antibiotics may be given, managed by the outpatient parenteral antibiotic team.
Drainage

Question 19

What is vertebral osteomyelitis

Answer 19

Acute haematogenous

Exogenous: after disc surgery, associated with implants

Question 20

Causative organisms in vertebral osteomyelitis

Answer 20

Staph aureus - 49%
Coagulase negative staph
Gram negative rods
Strep

Question 21

Common sites for vertebral osteomyelitis

Answer 21

Cervical
Cervico-thoraco
Lumbar

Question 22

Symptoms of vertebral osteomyelitis

Answer 22

Back pain
Fever
Neurological impairment

Question 23

Diagnosis of vertebral osteomyelitis

Answer 23

MRI: 90% sensitive
Blood cultures
CT/open biopsy

Question 24

Treatment of vertebral osteomyelitis

Answer 24

6 weeks of treatment

Longer treatment if undrained abscesses/implant associated

Question 25

76 year old man Admitted with a 4 month history of back pain with radiation down left leg Weight loss of 25kg over the last 6 months PMH: fracture right femur 25yrs ago in Kuwait. Metal plate inserted. Arthritis right knee, Hypertension. Lived in Iraq, Jordan and Singapore. Arrived in UK in 1993. MRI: discitis of L2/3 Spinal biopsy in September 2010 Tissue sent for culture. Coagulase negative staphylococci grown from enrichment. Histology : vague granuloma Empirical anti- tuberculous treatment commenced ( rifater and ethambutol) Empirical iv ceftriaxone commenced On 11.11.10 anterior L2/3 debridement and stabilisation Tissue- no growth Tissue sent for 16S PCR Serology- lyme, syphilis, brucella Brucella IgG > 1:2560 Brucella DNA present in spinal tissue Rifater, ethambutol and ceftriaxone was stopped Commenced rifampicin, ciprofloxacin and doxycycline

Answer 25

Just read through case

Question 26

Patient admitted after falling off a ladder in August 2009 to St. Elsewhere Was febrile. Blood cultures grew Salmonella sp. Treated with ciprofloxacin for 4 weeks Re-admitted to SMH with fever, loss of appetite. Blood culture again grew Salmonella (cipro resistant) MRI – showed discitis at L1/L2 and paravertebral collection Treated with ceftriaxone and azithromycin for 6 months Re-admitted with fever , hypotension Blood culture grew Salmonella (resistant to ciprofloxacin) Initially given meropenem and azithromycin, then switched to ceftriaxone and azithromycin Debridement and stabilisation of spine.

Answer 26

Chronic osteomyelitis

Question 27

Symptoms of chronic osteomyelitis

Answer 27

Pain Brodies abscess Sinus tract

Question 28

Diagnosis of chronic osteomyelitis

Answer 28

MRI | Bone biopsy for culture and histology

Question 29

Treatment of chronic osteomyelitis

Answer 29

Radical debridement down to living bone | Remove sequenstra, and remove infected bone and soft tissue

Question 30

What is the modified lautenbach technique

Answer 30

For chronic osteomyelitis Debridement and collection of multiple samples for culture and histology All internal fixation devices removed and double-ended reaming was performed Osteoscopy was used to ensure that healthy bleeding could be seen and any sequestra found was removed. Pulse lavage. Double lumen suction irrigation system was introduced through a subcutaneous tunnel. Post-op suction is applied for 30 mins Antibiotics are instilled through the central lumen followed by 1ml of streptokinase. The suction system was clamped for the next 3.5 hrs. Antibiotic instilled depended on culture results. Every week 1l of Hartmanns solution was infused through each drain . Suction fluid was sent for culture Irrigation was continued for 3 weeks usually Oral antibiotics were continued for 6 weeks after discharge After follow up for 101 months, 26 out of 35 patients had no signs of infection

Question 31

Papineau technique

Answer 31

For chronic osteomyelitis Complete excision of infected tissue and necrotic bone Open cancellous bone grafting of the osseous defect. Split skin grafting for wound closure Papineau reported a 93% success rate after treating 180 patients Panda et al reported an 89% success rate

Question 32

Signs and symptoms of prosthetic joint infections

Answer 32

Pain Patient complains that the joint was ‘never right’ Early failure Sinus tract

Question 33

Causes of prosthetic joint infections

Answer 33

``` Gram positive cocci -coagulase negative staphylococci -staphylococus aureus Streptococci sp Enterococci sp ``` Aerobic gram negative bacilli Enterobacteriaceae Pseudomonas aeruginosa Anaerobes Polymicrobial Culture negative Fungi

Question 34

Diagnosis of prosthetic joint infections

Answer 34

Radiology- loosening If CRP>13.5 for prosthetic knee joint infection CRP> 5 for prosthetic hip joint infection Joint aspiration: If >1700/ml of WCC correlates with knee PJI If > 4200/ml of WCC correlates with hip PJI May only get planktonic bacteria in joint fluid, may need to sample bacteria where infection is most likely

Question 35

Management of prosthetic joint infection

Answer 35

Intraoperative microbiological sampling: Tissue specimens from at least 5 sites around the implant Histopathology – infection defined as >5 neutrophils per high power field. If 3 or more specimens yield identical organisms, this is highly predictive of infection (sensitivity 65%, specificity 99%) Single stage revision: Remove all foreign material and dead bone Change gloves, drapes etc Re-implant new prosthesis with antibiotic impregnated cement and give iv antibiotics Two stage revision: Remove prosthesis Take samples for microbiology and histology Period of iv antibiotics (6weeks). Stop antibiotics for 2 weeks Re-debride and sample at second stage Re-implantation with antibiotic impregnated cement No further antibiotics if samples clear OPAT

Question 36

Endo Klink single stage revision for prosthetic joint infection

Answer 36

Aspirate joint to identify pathogen Excision of infected tissue , synovectomy Add antibiotics to bone cement according to culture results Implantation of a cemented hip or knee prosthesis using antibiotic loaded cement Give 7-10 days of iv antibiotics Culture drain tips Success rate is 89% in 2002

Question 37

Age- 70yrs old 1994 Right THR; 1998 Revision of acetabular component X-ray: lysis around distal part of femoral component Diabetic Most likely pathogen?

Answer 37

Samples form 1st stage grew coagulase negative staphylococci in 4 specimens Patient was started on iv vancomycin and oral rifampicin. 8 weeks later had 2nd stage . No growth from cultures