Lecture - Bone and Joint Infections Flashcards
Osteomyelitis:
- What is it and what structures may it involve?
- What are the three characteristics to classify it?
- It’s an inflammatory process of the bone that is secondary to infection (doesn’t have to be bacterial). It may involve periosteum, medullary cavity, compact or cancellous bone.
- DURATION (acute, subacute, chronic), ROUTE OF INFECTION (haematogenous aka through blood or exogenous aka outside of bone) and HOST RESPONSE (pyogenic or granulomatous aka where you form a granuloma?)
Osteomyelitis #2:
- What is the first route of infection?
- Why is haematogenous most common in children?
- Is it mono microbial or polymicrobial?
- What is the second route of infection?
- Why is it contiguous?
- Whereabouts in diabetics does it occur?
- Is it mono microbial or polymicrobial?
- Haematogenous = Organism in blood and then gets into bone
- Children - rich vascualr supply to ends (metaphysis). When BV come to supply, they become convoluted and thus vascular stasis so easier for organism to leave blood and get into bone. It’s just about the blood supply to growing bone
- Monomicrobial aka caused by single bacterial species - only one organism involved
- Exogenous - means it’s from outside of bone. It’s where it’s direct inoculation of the bone by the organism - might have been trauma, surgery etc.
- Contiguous aka it can be a local infection near bone that spread.
- Feet in diabetics - poor vasuclar supply in lower leg so will have ulcers etc so bacteria can spread
- Polymicrobial: Contingious infections of these sorts are often () aka a mix of bacteria causing infection
What are the two causes of (acute) osteomyelitis in terms of organisms that cause it?
- Haematogenous (aka caused by spread into blood). To some extent, the causes of these are specific to certain age groups. Staph aureus causes it haematogenous-ly in all three (newborns, children an adults)
- Direct inoculation/contiguous: also staph aureus to remember here
Osteomyelitis acute #3:
- What are 5 risk factors for it?
- IMMUNOSUPPRESSION
- AGE (children/elderly - At risk bc either their immune system just developing or as age - immune fucntion tends to decline)
- PVD: Peripheral vascular disease aka look at blood supply to bone annnnnd look at smokers because that damages vessels or something
- CHRONIC JOINT DISEASE: like RA - make joint very inflammed and leaky so organism can get into joint (chronic joint inflam can cause osteomyelitis) and then spread
- RECENT BONE SURGERY/REPLACEMENT/TRAUMA - provides route to enter
Osteomyelitis acute #4:
- Clinically, where do children get osteomyelitis and what sort of symptoms can you see? Are there more or less dramatic symptoms in infants?
- Where will you see it in adults? What sort of symptoms?
- Metaphysis (ends) of long bones. Symptoms are like severe pain, swelling, heat, redness, pseudoparalysis (wont wanna use limb that’s infected). Can happen in neonates and infants so they show generalised response aka period of lethargy and drowsy etc so can be challenege to see hwo seriois it is since they dont verbalise
- Spine, pelvis - will feel backache. It’s onset is less acute in adults than in kids but you still get paid, redness, swelling, fever etc
What’re complications that can occur in osteomyelitis? (acute)
- Spesis (organism can get into blood)
- Metastatic infection (Once in blood, it can travel to distant site or organ and then get eg abcess in other organ)
- septic arthritis (It could result in osteomyelitis or other way around)
- pathological fracture bc so much bone gets eaten away
- Chronic osteomyelitis
What’s the pathogenesis for osteomyelitis? (5) acute
- Inflammation: Infection (aka inflammation) in inelastic bone so pressure just keeps building so occulusion of blood flow and get ischaemia and necrosis. Osteolysis by enzymes collagenase and elastase released by immune cells
- Suppuration: pus formation and leak through sinus in chronic infection
- Sequestrum = Area of devitalised bone where no blood supply given
- Involcrum = it’s healing - you form new bone (sometimes may occur over sequestrum). Sequestrm gets reaborbed and you get healing and things get to normal buuuuut sometimes sequestrum gets left behind and that cna become source of reactivation of osteomyelitis later down the track
- Resolution or progression to complication
Three ways to diagnose osteomyelitis? (acute)
- Culture/stain: Get some sort of pus from the site of infection
Culturing any sort of the draining pus through since but its not a good correlation of what’s in pus and what’s causing infection unless you find staph aureus in pus then it’s most likely the thing causing the infection but otherwise dont culture the pus coming out
Sometimes cant isolate the organism
Blood culutre also good sample if cant find organism in osteomyleitis
Have a smear of pus (inflam cells) and can fee firbrin etc and see gram +ve cocci in clusters
This can direct initial antimicrobial therapy
Also, best results if taken before antimicrobial therapy
Can even see leukocytosis and raised CRP
- Bone scans: Radioactive isotope gets incorported into bone/sites of infection so useful bc can diagnose very early osteomyelitis aka within a few dyas of onset of infection (x rays not useful earlier) but slight drawback that get false positives if other infections cause the test to be positive and not the one in the bone
- Imaging studies: x-rays take a long time aka 10-14 days before osteomyelitis visible in x-ray and by then, 40% less bone so not good for trying to diagnose early infection.
CT scans useful for bones which are difficult to x ray but need at least 1 week
MRI is useful for early diagnosis but it’s hard to access
What’re the two treatments for osteomyelitis? (acute)
- MEDICAL: Needs rapid (empric) treatment so treat with antimicrobial before even know what the organism is. Once get culture, need to target the organism specifically (antimicrobial stewardship) not killing off anything else
Need prolonged therapy which can then be changed to oral therpay (from IV) so long course of drug to treat these infections. Children you can give oral only but combination of oral and IV Is good when you’ve establish the thing
- SURGICAL: Debridement to remove any foreign objects or necrotic bone. Amputation in diabetics but that’s extreme
Subacute osteomyelitis:
- What abscess can you get?
- What age group does it generally occur in?
- What’s the diagnosis? (2)
- What about treatment? (2)
- Brodie’s abscess - localised osteomyelitis (staph aureus abscess in bone)
- Happens generally in adults with few clinical signs and little to no pain - might persist over the years
- Aspiration or biopsy of abscess (only half the cases will grow). Or x-ray: Useful in this instance bc it’s a long standing process and have lots of damange to bone (can see abcess in pic on right)
- Long course antimicrobials or surgical debridement
Chronic osteomyelitis
- Two ways it can arise?
- Poly or mono microbial?
- Pyogenic or granulomatous?
- Two ways to diagnose
- Treatment (2)
- Sequestrum can act as a source of infection or it can arise post-surgical treatment.
- DIfferent to acute form bc this is poly-microbial (caused by mix of different bac)
- Gramulomatous (TB, syphilis)
- Diagnosis = Culture staining or imaging (use x ray bc looking at big destruction of bone)
- Long course antimicrobial therapy or surgical debridement (sequestrectomy)
Septic arthritis #1:
- What is it?
- What three things is it characterised by?
- Invasion of the joint by pathogen which produces arthritis. Bacteria are most damaging but fungi or virus can also cause it. Acute/chronic disease can also cause it
- Colonisation of synovial fluid, influx of inflammatory/immune cells, erosion of synovial membrane (Produce fluid and then damage synovial membrane with I think enzymes etc?)
What’s the cause for acute vs chronic septic arthritis?
Actue: 60-80% staph aureus
Chronic: HIV, Rubella, TB, syphillis, fungi (Candida)
Septic arthritis #2:
- Increasing incidence in what cause?
- What are some risk factors for it?
- Joint surgery/replacement: bc potential target for some microbes
- if early onset (less than 3 months post-implant) then staph aureus
- if 3-24 months then staph epidermidis (bc it makes biofilms on foreign surfaces) REMEMBER THIS
- More than 24 months: haematogenous spread - Previously damaged joints (RA, grout etc) so existing inflammation or damage to defence mechanisms
- Immunosuppression
- Male
- More than 65
- Joint replacement surgery
What’re the clinical symptoms of septic arthritis?
Acute, acid onset of inflammation and swelling
Severe arthralgia (joint pain)
- Pseudoparalysis
- Low-grade fever
- Monoarticular
- Could be polyarticular if staph aureus or gonoccus