Bone and Soft Tissue Infection Flashcards
What is the epidaemiology of acute haematogenous osteomyelitis?
(Who is it more common in? What is it associated with?)
Haematogenous spread is mostly children (different ages)
boys > girls
Associated with diabetes, rheumatoid arthritis, immune compromise, long-term steroid treatment, sickel cell
What should you look for in a history when you suspect acute haematogenous osteomyelitis?
History of trauma (minor)
What can be a source of infection in acute osteomyelitis?
3 general sources + Infants, children and adults
Haematogenous spread - children and elderly
Local spread from contaguous site of infection - trauma (open fracture), bone surgery (ORIF), joint replacement
Secondary to vascular insufficiency
In infants: infected umbilican cord
In children: boils, tonsilitis, skin abrasions
In adults: UTI, arterial line
What organisms cause acute osteomyelitis in infants?
under 1 year
Staph aureus
Group B streptococci
E. coli
What organisms cause acute osteomyelitis in older children?
Staph aureua
Strep pyogenes
Haemophilus influenzae
What organisms cause acute osteomyelitis in Adults?
Staph aureua
Coagulase negative staphylococci (prostheses)
Propionibacterium spp (prosthesus)
Streptococci pyogenes (infectious arthritis)
Mycobacterium tuberculosis
Pseudomonas aeroginosa (esp secondary to penetrating foot injuries, IVDAs)
Acute osteomyelitis in butchers may be caused by what organism?
Brucella
Acute osteomyelitis in fishermen, filleters may be caused by what organism?
Mycobacterium marinum
When may candida cause acute osteomyelitis?
- Debilitating illness,
- HIV AIDS,
- long term antibiotic treatment,
- extensive GI surgery,
- malignancy
What 2 special cases may cause mixed infection acute osteomyelitis?
Diabetic foot (mixed infection including anaerobes)
Pressure sores
What organisms can cause vertebral and sternal acute osteomyelitis?
Vertebral
- S. aureus
- TB
Sternal:
-Coagulase negative staphylococci post cardiac surgery
What two conditions can result in acute osteomyelitis caused by salmonella spp and gonococcus?
Sickle cell disease -> salmonella spp
STD - gonococcus
Describe the pathology of osteomyelitis
Starts at metaphysis - role of trauma?
Vascular stasis
(venous congestion + arterial thrombus)
Acute inflammation - increased pressure
Suppuration
Release of pressure
(medulla, sub-periosteal, into joint)
Necrosis of bone (sequestrum)
New bone formation (involucrum)
Resolution - or not (chronic osteomyelitis)
Give 3 examples of long bones with their metaphysis outside the joint
Distal femur
Proximal tibia
Proximal humerus
Give two examples of joints with intra-articular metaphysis
Hip
Elbow (radial head)
What is involucrum?
An involucrum (plural involucra) is a layer of new bone growth outside existing bone seen in pyogenic osteomyelitis. It results from the stripping off of the periosteum by the accumulation of pus within the bone, and new bone growing from the periosteum.
It can be seen radiographically (i.e., with x-rays), although it is seen rarely in developed countries, given that osteomyelitis is rarely left untreated there.
What is a sequestrum?
A sequestrum (plural: sequestra) is a piece of dead bone that has become separated during the process of necrosis from normal or sound bone.
Describe the pathological process of sequestrum
- Infection in the bone leads to an increase in intramedullary pressure due to inflammatory exudates
- The periosteum becomes stripped from the osteum, leading to vascular thrombosis (granulation tissue “walls off” sequestrum)
- Bone necrosis follows due to lack of blood supply (adjacent healthy bone is devascularised, causing further destruction)
- Sequestra are formed
What are the clinical features of acute osteomyelitis in a child?
Severe pain
Reluctant to move (neighbouring joints held flexed); not weight bearing
May be tender and inflammed
Fever (swinging pyrexia) + tachycardia
malaise (fatigue, N+V - “Nae weel”)
Toxaemia
What are the clinical features of acute osteomyelitis in an infant?
May be minimal signs, or may be very ill
Failure to thrive
Possibly drowsy or irritable
Metaphyseal tenderness + swelling
Decreased ROM
Positional change
Commonest around knee
What are the clinical features of an adult with acute osteomyelitis?
Both primary and secondary
Primary OM seen commonly in thoracolumbar spine fever
- Backache
- History of UTI or urological procedure
- Old, diabetic, immunocompromised
Secondary OM much more common
- Often after open fracture, surgery (esp. ORIF)
- Mixture of organisms
How do you diagnose acute osteomyelitis?
list the diagnostic tests -> bloods, imaging etc
History and clinical examination (pulse and temp)
FBC + diff WBC (neutrophil leucocytosis)
ESR, CRP
Blood cultures x3 (at peak temp -> 60% positive)
U+Es- ill, dehydrated
X-ray (normal in first 10-14 days)
USS
Aspiration
Isotope bone scan (Tc-99, Gallium-67)
Labelled white cell scan (Indium-111)
MRI
How can you make a microbiological diagnosis in acute osteomyelitis?
Blood cultures in haematogenous ostemyelitis and septic arthritis
Bone biopsy
Tissue or swabs from up to 5 sites around implant at debridement in prosthetic infections
Sinus tract and superficial swab results may be misleading (skin contaminants)
What is the differential diagnosis of acute osteomyelitis?
Acute septic arthritis
Trauma (fracture, dislocation etc)
Acute inflammatory arthritis
Transient synovitis (“irritable hip”)
Rare:
- Sickle cell crisis
- Gaucher’s disease
- Rheumatic fever
- Haemophilia
How do you treat acute osteomyelitis?
Supportive treatment for pain and dehydration
-general care, analgesia
Rest and splintage
Antibiotics
- Route (IV/oral switch - 7-10 days?)
- Duration (4-6 wks - depends on response, ESR)
- Choice - empirical (Fluclox + BenylPen) while waiting
Give some reasons for antibiotic “failure”
Drug resistance - e.g. lactamases
Bacterial persistence - “dormant” bacteria in dead bone
Poor host defences - IDDM, alcoholism…
Poor drug absorption
Drug inactivation by host flora
Poor tissue penetration
Give 4 indications for surgery in acute osteomyelitis
Aspiration of pus for diagnosis and culture
Abscess drainage (multiple drill-holes, primary closure to avoid sinus)
Debridement of dead/ infected/ contaminated tissue
Refractory to non-operative Rx >24-48hrs
Give some complications of acute osteomyelitis
Septicaemia, death
Metastatic infection
Pathological fracture
Septic arthritis
Altered bone growth
Chronic osteomyelitis
Give 3 reasons why subacute osteomyelitis may occur over acute osteomyelitis
Increased host resistance
Lower bacterial virulence
Antibiotic usage
What are the clinical features of subacute osteomyelitis?
Long history (weeks, months)
Variable symptoms (pain, limp)
Local swelling/ warmth occasionally
Tenderness
What is the differential diagnosis for subacute osteomyelitis?
Tumour - Ewing’s sarcoma, osteoid osteoma
TB
What is Brodie’s abscess?
(What is it? Who does it occur in? What are its features?
A well defined cavity in cancellous bone
A Brodie abscess is a type subacute osteomyelitis
Older children
Painful limp, no systemic features
Radiographic lucency in long bone metaphysis
What is the differential diagnosis of Brodie’s abscess?
Ewing’s sarcoma
What is the treatment for Brodie’s abscess?
Curettage
What are the investigations for subacute osteomyelitis?
X-ray
Bone scan
Biopsy (50% +ve) grow oragism
What is the treatment for subacute osteomyelitis?
Prolonged course of antibiotics
Surgery - curettage
What can cause chronic osteomyelitis?
May follow acute osteomyelitis (now much rarer in children)
May start de novo
- Following operation
- Following open fracture (possibly many years later)
- Immunosuppressed, diabetes, elderly, drug abusers etc)
Repeated breakdown of “healed” wounds
What is the definition of chronic osteomyelitis?
Chronically discharging sinus fixed to the underlying bone containing sequestrum surrounded by infected granulation tissue and involucrum
What organisms usually cause chronic osteomyelitis?
Often mixed infection
usually same organism(s) each flare up
Mostly Staph. Aureus, E. Coli, Strep. Pyogenes, Proteus
What is the pathology of chronic osteomyelitis?
What 3 features can it be boiled down to?
Sequestrum + involucrum + sinus
What is the treatment for chronic osteomyelitis?
Long term antibiotics?
- local (gentamicin cement/beads, collatamp)
- Systemic (orally/ IV/ home AB)
Eradicate bone infection - surgically (multiple operations)
Treat soft tissue problems
Deformity correction?
Massive reconstruction?
Amputation?
What are the complications of chronic osteomyelitis?
Chronic discharging sinus + flare ups
Ongoing (metastatic) infection (abscesses)
pathological fracture
Epithelioma
Growth disturbance + deformities
Amyloidosis
Squamous cell carcinoma (0.07%)
What is the route of infection in acute septic arthritis?
Direct invasion
- Penetrating wound (iatrogenic? - joint injection)
- I/A injury
- Arthroscopy
Eruption of bone abscess
Haematogenous
Metaphyseal septic focus
What are the two outcomes of a metaphyseal septic focus?
Spread into either joint cavity -> septic arthritis
OR
Spread into periosteum -> osteomyelitis
What are the common oragnisms of acute septic arthritis?
Staphylococcus aureus
Haemophilus influenzae
Streptococcus pyogenes
E. Coli
What is the pathology of acute septic arthritis?
Acute synovitis with purulent joint effusion
Articular cartilage attacked by bacterial toxin and cellular enzyme
Complete destruction of the articular cartilage
What are the sequelae of acute septic arthritis?
outcomes
Complete recovery
OR
partial loss of the articular cartilage and subsequent OA
OR
Fibrous or bony ankylosis
What are the clinical features of acute septic arthritis in a neonate?
Picture of septicaemia
- Irritability
- Resistant to movement
- Ill
What are the clinical features of acute septic arthritis in a child?
Acute pain in a single large joint
- Reluctant to move the joint (ANY movement- c.f. bursitis where RoM ok)
- Increased temp and pulse
- Increased tenderness
What are the clinical features of acute septic arthritis in an adult?
Often involves superficial joint (knee, ankle, wrist)
Rare in healthy adult
What are the investigations for acute septic arthritis?
FBC, WBC, ESR, CRP, blood cultures
X-ray
USS
Aspiration
What is the most common cause of acute septic arthritis in adults?
Wat can it result in?
Infected joint replacement
Rare (1-1.5%) but disaster (death, amputation, removal of arthroplasty
Changing picture of organisms, but Staph still most common
What is the differential diagnosis of acute septic arthritis?
Acute osteomyelitis Trauma Irritable joint Hemophilia Rheumatic fever Gout Gaucher's disease
How do you classify tuberculosis of the bone and joint?
Extra-articular (epiphyseal/ bones with haemodynamic marrow)
Intra-articular (large joints)
vertebral body
Does bone and joint TB involve single or multiple lesions?
Multiple lesions in 1/3 of patients
So 2/3 have single
What are the clinical features of tuberculosis of the bone and joint?
Insidious onset and general ill health
Contact with TB
Pain (esp. at night), swelling, loss of weight
low grade pyrexia
Joint swelling
Decrease ROM
Ankylosis
Deformity
Why is there poor entry of antibiotics in bone and joint TB?
Obliterative endarteritis
What are the 2 stages of bone and joint TB?
Early short lived vascular
Chronic avascular
How do you diagnose bone and joint TB?
Long history
Involvement of single joint
Marked thickening of the synovium
Marked muscle wasting
Periarticular osteoporosis
What are the investigations for TB?
FBC, ESR
Mantoux test
Sputum/ Urine culture
X-ray
- Soft tissue swelling
- Periarticular osteopaenia
- Articular space narrowing
Joint aspiration and biopsy
- AAFB identified in 10-20%
- Culture +ve in 50% of cases
What is the differential diagnosis of bone and joint TB?
Transient synovitis
Monoarticular RA
Haemorrhagic arthritis
Pyogenic arthritis
