Wound, Bone and Joint Infections Flashcards
Most common causes of surgical site infections
Staph aureus (MSSA and MRSA) E.coli Pseudomonas aeruginosa
Causes of surgical site infections
Contamination of wound at operation
Pathogenicity and innoculum of microorganisms
Host immune response
Pathogenesis of surgical site infections
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
Three levels of surgical site infection
Superficial incisional - affects skina dn subcutaneous tissue
Deep incisional - affect fascial and muscle layers
Organ/space infection - any part of anatomy other than incision
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?
IV linezolid
Preventing surgical site infections (when can interventions be done)
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
Risk factors for surgical site infections
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.
Management of infected/colonised surgical personnel
Encourage surgical personnel who have symptoms of a transmissible infection to report to occupational health.
Bone and joint infections
Septic arthritis
Vertebral osteomyelitis
Chronic osteomyelitis
Prosthetic joint infection
Risk factors for septic arthritis
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
Pathophysiology of septic arthritis
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
Bacterial factors causing infection in septic arthritis
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.
Host factors causing infection in septic arthritis
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.
Causative organisms in septic arthritis
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
Clinical features of septic arthritis
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
