Infections of the Bone Flashcards
describe the clinical approach to infection
Clinical suspicion – history is key
- Examination
Confirmation
- Indirect – CT scan, MRI best
-
Direct – gold standard is bone biopsy
- Surgical sample, histology
- Wound swabs/blood cultures (useful in septic patients) are not very helpful
Treatment:
- Debridement
-
Antimicrobials
-
Await microbial diagnosis
- Unless acute presentation or sepsis
-
Await microbial diagnosis
describe the approach to antimicrobial prescribing
await microbial diagnosis, unless acute presentation or sepsis
how will the patient typically present
- Acute illness with extreme pain over affected bone
- Tenderness, warmth, swelling and erythema of the affected part
- Unwillingness to move limb
- Signs of systemic infection
osteomyelitis
inflammation of the bone and medullary cavity
where is OM usually seen
in the metaphyses of long bones
predisposing conditions
- Sickle cell anaemia
- IV drug user
- DM
- Immunosuppression
- alcohol excess
how long must the ABx course be
minimum 6 weeks
summarise what happens in the bone in osteomyelitis
bone necrosis and reactive bone formation
which forms of acute osteomyelitis can progress to chronic?
all
how do bacteria cause bone inflammation
bacteria lodge in metaphyseal blood vessels and set up an inflammatory reaction in the medullary canal, which spreads through the cortex, elevates the periosteum and may spread locally into an adjacent joint (septic arthritis)or into blood vessels(bacteraemia and septicaemia)
what does interference with bone blood supply cause
bone death and formation of sequestrum (dead fragment of bone) embedded in pus/infected granulation tissue
the sequestra are surrounded by sclerotic bone which is relatively avascular
within the bone the Haversian canals become blocked with scar tissue and the bone becomes surrounded by thickened periosteum
why is chronic osteomyelitis so hard to treat
due to avascular nature of the sequestra ABx will not travel to site via blood stream
involucrum
- Periosteum lays down a new shell of bone called involucrum surrounding the existing sequesta
- This is new, immature bone that forms around the seqestrum, effectively sealing it off
why is S Aureus particularly difficult to eradicate
can infect osteocytes intracellularly and decreases the activity and viability of osteoblasts
who does an acute osteomyelitis in the absence of recent surgery tend to occur in
kids
IC adults
describe 3 mechanisms of acute osteomyelitis in children
- the metaphyses of long bones contain abdundant tortuous vessels with sluggish flow which can result in the accumulation of bacteria and infection spreading towards the epiphysis
- some metaphyses are intra articular (proximal femur, humerus, radial head and ankle), therefore infection can spread into a joint causing co-existing septic arthritis
- loosely applied periosteum so an abscess can extend widely along the sub periosteal space
Brodie’s abscess
- onset
- who is it usually found in
- describe the pathology
form of localised subacute or chronic osteomyelitis with a more insidious onset
found in children
central cavity containing pus (which may be sterile) lined by granulation tissue and surrounded by reactive bone sclerosis
chronic osteomyelitis
develops from an untreated acute osteomyelitis and may be associated with sequestrum and/or involucrum
can be suppressed with ABx and lay dormant for years before reactivating
where does chronic osteomyelitis tend to be in adults
axial skeleton (spine or pelvis) or intervertebral disc
what can TB cause
chronic osteomyelitis, particularly in the spine through haematogenous spread from primary lung infection
what must one do to the sequestrum in the treatment of osteomyelitis
physically remove it
what investigations are useful in chronic osteomyelitis
blood tests are not
X ray and MRI are
treatment of chronic osteomyelitis
ABx alone wont work
surgery to remove sequestrum and debride
fixation of bone if there is instability
what can diffuse osteomyelitis result in
skeletal instability (eg infected non union)
what are the benefits of external fixation if the bone has been shortened by debridement
it can be subsequently lengthened
who is at particular risk of OM of the spine
poorly controlled DM, IV drug abusers, IC patients
complications of spinal surgery
where is the most common location for osteomyelitis in spine
lumbar spine
how do patients with osteomyelitis of the spine present
- insidious onset of back pain which is constant and unremitting
- paraspinal muscle spasm and spinal tenderness
- fever and systemic upset
- severe cases may be associated with neurological deficit
what can eventually happen to vertebra due to osteomyelitis
vertebral end plates weaken and eventually collapse leading to kyphosis or vertebra plana
investigations for osteomyelitis in spine
MRI - extent of infection and abscess formation
blood cultures - causative organism
endocarditis should be considered
treatment of osteomyelitis of the spine and indications for surgery
- high dose IV ABx after CT guided biopsy to obtain tissue culture
- indications for surgery are inability to obtain cultures by needle biopsy, no response to ABx, previous vertebral collapse and neurological deficit
- surgery involves debridement, stabilisation and fusion of adjacent vertebrae
what is the gold standard investigation
bone biopsy
MRI
normal ABx prescribed
flucloxacillin for 6 weeks
complications
- Septicemia
- Acute pyogenic arthritis
- Growth retardation
- Chronic osteomyelitis
management of open fractures
- Cover wound with dressing
- Broad spectrum antibiotics (IV)
- Ensure tetanus immunisation
- Early debridement in theatre
clinical clue for open fracture
non union and poor wound healing
which patient groups commonly get OM from haematogenous spread
- prepubertal children
- PWID
- central lines, dialysis, elderly
pathogens implicated in PWID
- Staphylococcus, Streptococci and often unusual pathogens (Pseudomonas, TB, candida, Eikenella Corrodens
Eikenlla Corrodens
- causes OM in PWID
- ‘needle lickers’
osteitis pubis
- inflammation over the pubic symphysis
- presents with localised pain radiating outwards
what can predispose one to the bacterial type of Osteitis Pubis
urogynaecological procedures
what can cause the sterile type of Osteitis Pubis
- complication of invasive (surgery) procedure about the pelvis (can occur up to 18 months later)
- may occur as an inflammatory process in athletes
what is the common causative organism in sickle cell anaemia patients
salmonella
sickle cell anaemia
- Sickle cell anaemia is an autosomal recessive genetic disorder characterised by the synthesis of defective haemoglobin – HbS.
- These are deformed and rigid and lead to frequent clotting and thrombosis of blood vessels.
- The consequence of obstruction is ischemia and infarction.
- Results in small localised areas of dead tissues.
what is the DD of OM in sickle cell anaemia
bone infarction
are there single or multiple lesions in OM sickle cell anaemia
- can be multifocal
- seen in the long bones
Gaucher’s disease
- lysosomal storage disease in which glucocerebroside accumulates in cells and certain organs eg bones
- can manifest as a bone crisis (severe bone pain as a result of infarction)
which bone does Gaucher’s disease oftne affect
the tibia
pathogens implicated in Gaucher’s disease
- if just a bone crisis is sterile
- S Aureus if infected
SAPHO
- Synovitis, acne, pustulosis, hyperostosis and osteitis
- hypertosis means abnormal excessive growth of bone, frequently located in chest wall
- Osteitis often occurs at sacroiliac joints and spine
CRMO
- Autoimmune disease similar to osteomyelitis, but without the infection
- involves multiple bones at different times
- may be related to SAPHO
diagnosis of SAPHO and CRMO
- History plus culture samples are needed to exclude osteomyelitis
- Raised inflammatory markers
- Lytic lesions of X rays
- Multifocal
general symptoms of SAPHO and CRMO
can cause fever, weight loss and malaise
which bacteria may play a role in SAPHO and CRMO
Proprionibacterium
which is found in adults and which in kids - SAPHO and CRMO
- SAPHO in adults
- CRMO in kids
Pott’s disease
TB in the spine that has spread haematogenously from eg the lungs
features of Pott’s disease
- Clinical Features: backache and stiffness of all back movements
- Eventually leads to caseous necrosis, vertebral collapse and gibbus
- May be abscess formation
what test would you offer in adults with Pott’s
HIV
planktonic bacteria
is free in the blood
sessile bacteria
- sits on prosthetic/joint and forms a biofilm
- phenotypic transformation of sessile bacteria
what bacteria are implicated in prosthetic joint infection
- S aureus
- S epidermidis
- Propionibacterium acnes
- E coli
- Pseudmonas aeruginosa
diagnosis of prosthetic joint infection
- culture perioperative tissue
- CRP
- radiology
coauglase negative staph in infections
- they are part of the normal flora eg epidermidis, so have a low virulence and can only cause infection in the presence of prosthetic material
- They produce a surface polysaccharide slime which allows them to stick to the materia
initial treatment of staph epidermidis
- vancomycin
- often add rifampicin
what happens to the prosthetic joint if it is infected
- Ideally the prosthetic joint is removed if it is causing infection, this can be done in 1 or 2 stages
- In some elderly people the joint is not removed and is just debrided, but this has a poor prognosis
which joint is most commonly affected by septic arthritis
knee
when must septic arthrtis be considered
consider in any acutely inflamed joint as it can destroy a joint in under 24 horus
what often causes septic arthritis in sexually active people
neisseria gonorrhoea
what commonly causes septic arthritis in pre school children
H influenzae, rarely seen now due to vaccination
diagnosis of septic arthritis
- Clinical picture
- Urgent joint aspiration for synovial fluid microscopy and culture is the key investigation
- Blood culture if pyrexial
- Gout can present in the same way so exclude crystals
treatment of septic arthritis
- presumptive flucloxacillin to cover S aureus
- if under 5 add ceftriaxone for H influenzae
pyomyositis
Bacterial infection of the skeletal muscles that results in a pus-filled abscess
which organisms often cause pymyositis in infected wounds
clostridium ones
common cause of pymyositis
S aureus
what is tetanus caused by
- Clostridium tetani
- Gram positive strictly anaerobic rods
- Forms spores, which are found in soil etc.
- The exotoxin causes muscle spasms and rigidity.
classical description of tetanus
- locked jaw
- spasms can be induced by loud noises and bright lights
treatment of tetanus
- Surgical debridement
- Antitoxin
- Supportive measures
- Antibiotics are not that useful as it is due to toxin
- Survivors are not immune – booster vaccine
