Bone and Soft Tissue Infection

Question 1

OM

Answer 1

Bone infection

Question 2

SA

Answer 2

Joint infection

Question 3

Types of OM

Answer 3

Acute (days/wks)
Chronic (months/years) - assoc with avascular necrosis and sequestrum formation within bone
Specific - e.g. TB
Non-specific

Question 4

Where OM affects most

Answer 4

Long bones of legs and arms in kids
Vertebrae in adults
Diabetics may get it in their feet if they are ulcerated

Question 5

Who gets OM?

Answer 5

Mostly kids

Hx of minor trauma or other dx (e.g. DM, RA, immunocompromised, long term steroids Rx, sickle cell)

Question 6

Sources of infection of OM

Answer 6

Haematogenous spread (bodily infection –> organism enters BS –> infiltrates BM –> localised systemic reaction)

Localised spread from contagious site of infection (e.g. open fracture, bone surgery, joint replacement)

Secondary to vascular insufficiency, reduced WCC to dispose of microbes reaching bones (dx affecting circulating, e.g. DM, sickle cell)

Question 7

Organisms infecting <1y

OM

Answer 7

Staph aureus
GBS
E. coli

Question 8

Organisms infecting older children

OM

Answer 8

Staph aureus
Strep pyogenes
H. influenzae

Question 9

Organisms infecting adults (OM)

Answer 9

Staph aureus
Coagulase negative staphylococci (prostheses)
propionbacterium spp (protheses)
Myobacterium tuberculosis
Pseudomonas (secondary to penetrating injuries, IVDA)

Question 10

Organisms infection diabetic foot and pressure sores (OM)

Answer 10

Mixed incl. anaerobes

Question 11

Organisms infecting those with sickle cell dx (OM)

Answer 11

Salmonella

Question 12

Organisms infecting fishermen, filleters (OM)

Answer 12

Mycobacterium marinum

Question 13

Organisms infecting those with debilitating illness/HIV

Answer 13

Candida albicans

Question 14

Where does AOM tend to affect?

Answer 14

Metaphysis of long dose (e.g. distal femur, proximal tibia/humerus) or joints with intra-articular metaphysis (e.g. hips, elbow)

METAPHYSIS MOST COMMON SITE as sluggish BF, fewer phagocytic cells

Bacteria settle in metaphysis –> acute inflammation –> increased pressure –> suppuration –> release of pressure as pus moves into medulla, subperiosteum and joint

Necrosis of bone (sequestrum)

New bone formation (Involucrum)

Can either resolve or –> COM

Question 15

What are the CFs of OM in infants?

Answer 15

Minimal signs --> v. ill
FFT
Drowsy/irritable
Metaphyseal tenderness/swelling
Decreased RoM 
Positional change
Commonest around knee

Question 16

What are the CFs of OM in children?

Answer 16

Severe pain w. reluctance to move (neighbouring joints flexed)
Fever, tachycardia
Malaise, fatigue, NV, toxaemia

Question 17

What are the CFs of OM in adults?

Answer 17

Tends to be after open fracture or surgery

Question 18

How do you diagnose OM?

Answer 18

Hx Ex (pulse, temp) 
Suspect if local symptoms and non-specific signs/symptoms of inflammation 

Blood tests - FBC, differential WCC, ESR, CRP, blood cultures x3 (at peak of temp), UE

Imaging

Bone biopsy for definitive diagnosis
Swabs/tissue in prosthetic infections

Question 19

Imaging for OM

Answer 19

XRay (normal in first 14 days) 
USS
Aspiearion 
Isotope bone scan 
Labelled white cell scan 
MRI - best

Question 20

Xray signs of OM

Answer 20

Early - minimal change
Early periosteal changes - lytic lesions in medullary cavity
Late periosteal changes - sequestrum formation (dead bone separating)
Involucrum - layer of new bone growth outside existing bone

Question 21

Differentials of OM

Answer 21

Acute SA
Acute inflammatory arthritis
Trauma
Transient synovitis
Sickle cell crisis, rheumatic fever
Soft tissue infection (e.g. cellulitis, erysipelas)

Question 22

Complications of OM

Answer 22

Septicaemia
Death 
Metastatic infection 
Pathological fracture
SA
Altered bone growth 
Chronic OM

Question 23

Management of OM

Answer 23

Supportive for pain/dehydration 
Analgesia
Rest, splintage
Antibx - flucolox and benzylpen empirical (IV --> oral) 
Surgery

Question 24

Reasons for antibx to fail in OM Rx

Answer 24

Drug resistance
Bacterial persistence
Poor host defences, e.g. IDDM, alcoholism
Poor drug absorption 
Drug inactivated by host flora
Poor tissue penetration

Question 25

Indications for surgery in OM

Answer 25

Aspiration of pus for culture/diagnosis
Abscess drainage
Debridement/lavage of dead/infected/contaminated tissue
Refractory to non-op Rx >24-48h

Question 26

Aetiology of chronic OM

Answer 26

Following acute OM
Following op, open fracture
Immunosupressed, DM, elderly, drug abusers,
Repeated breakdown of healed wounds

Question 27

Organisms causing chronic OM

Answer 27

Staph aureus, E. coli, strep pyogenes, proteus

Question 28

What is the pathology of COM?

Answer 28

Cavities, sinuses
Dead bone (retained sequestra)
Involucrum
Chronic inflammation histologically

Question 29

Complications of COM

Answer 29

Chronically discharging sinus and flare ups 
Ongoing metastatic infection 
Abscess formation 
Pathological fractures
Growth disturbance and deformities
Squamous cell carcinoma

Question 30

Mx of COM

Answer 30

Local gentamicin cement/beads
System IV/oral antibx
Rx soft tissue problems
Deformity correction? Massive reconstruction? Amputation?

Question 31

Routes of infection of SA

Answer 31

Haematogenous (e.g. septicaemia)
Eruption of bone abscess
Direct invasion (e.g. penetrating wound, IA injury, iatrogenic (joint infection, arthroscopy)

Question 32

RFs for SA

Answer 32

Prosthetic implant

Damaged joints, e.g. RA

Question 33

Aetiology of SA

Answer 33

Infected joint replacement most common

Metaphyseal septic focus can lead to either septic arthritis/OM

Question 34

SA most common organisms

Answer 34

STAPH AUREUS, H. influenzae, strep pyorgenes, E. coli

Question 35

Pathology of SA

Answer 35

Acute synovitis w. purulent joint effusion

Articular cartilage attacked by bacterial toxin and cellular enzymes –> complete destruction of articular cartilage

Question 36

Sequlae of SA

Answer 36

Complete recovery or
Partial loss of articular cartilage and subsequent OA or
Fibrous/bony anklylosis –> dec. RoM

Question 37

Neonatal presentation of SA

Answer 37

Irritability, resistant to movement, ill

Question 38

Child/adult presentation og SA

Answer 38

Acute pain in single joint
Reluctance to move joint 
Fever and tachycardia
Tenderness
Joint swelling/redness/hot

In adults often knee

Question 39

Ix SA

Answer 39

FBC, WBC, ESR, CRP, blood cultures
USS, XRay (?OM, concurrent join), aspiration (arthocentesis - removal of synovial fluid from joint effusion, diagnostic and therapeutic - red. pressure –> red. pain) - req. for definitive diagnosis

Question 40

Differentials SA`

Answer 40

Acute OM 
Trauma
Irritable joint
Haemophilia 
Rheumatic fever
Gout

Question 41

Mx SA

Answer 41

Analgesia
Antibx (3-4w)
Arthrocentesis
Surgical drainage - emergency, open/arthroscopic lavage
Infected joint replacements - 1/2 stage revision
Rehab and physio

Question 42

TB classification

Answer 42

Extra-articular
Intra-articular
Vertebral body

Question 43

CF TB

Answer 43

Insidious onset and general ill health 
Contact with TB 
Pain, esp at night, swelling, wt loss, fever
Joint swelling, reduced RoM
Anklyosis
Deformity

Question 44

Pathology TB

Answer 44

Primary complex in lung/gut
Secondary spread common in joints/bone
Tuberculous granuloma
Malnutrition/HIV/AIDs predispose to TB

Question 45

CF spinal TB

Answer 45

Little pain

Present with kyphosis/abscess

Question 46

Diagnosis of TB

Answer 46

Long Hx affecting single joint

Marked thickening of synovium, marked muscle wasting, periarticular osteoporosis

Question 47

Ix TB

Answer 47

FBC, ESR 
Mantoux test
Sputum/urine culture
XRay - soft tissue swelling, periarticular osteopenia, articular space narrowing
Joint aspiration & biopsy (AAFB)

Question 48

Differentials TB

Answer 48

TS
Monoarticular RA
Haemorrhagic arthritis
Pyogenic arthritis
Tumour

Question 49

Mx TB

Answer 49

2 months - rifampicin, isoniazid, ethambutol

6-12m: rifampicin, isoniazid

Rest, splintage, op drainage sometimes