Bone and Soft Tissue Infection Flashcards by Aimee Love

Bone infection

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Joint infection

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Types of OM

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

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Where OM affects most

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

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Who gets OM?

Mostly kids

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

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Sources of infection of OM

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)

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Organisms infecting <1y

Staph aureus
GBS
E. coli

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Organisms infecting older children

Staph aureus
Strep pyogenes
H. influenzae

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Organisms infecting adults (OM)

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

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Organisms infection diabetic foot and pressure sores (OM)

Mixed incl. anaerobes

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Organisms infecting those with sickle cell dx (OM)

Salmonella

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Organisms infecting fishermen, filleters (OM)

Mycobacterium marinum

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Organisms infecting those with debilitating illness/HIV

Candida albicans

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Where does AOM tend to affect?

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

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What are the CFs of OM in infants?

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

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What are the CFs of OM in children?

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

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What are the CFs of OM in adults?

Tends to be after open fracture or surgery

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How do you diagnose OM?

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

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Imaging for OM

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

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Xray signs of OM

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

Differentials of OM

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

Complications of OM

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

Management of OM

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

Reasons for antibx to fail in OM Rx

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

Indications for surgery in OM

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

Aetiology of chronic OM

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

Organisms causing chronic OM

Staph aureus, E. coli, strep pyogenes, proteus

What is the pathology of COM?

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

Complications of COM

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

Mx of COM

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

Routes of infection of SA

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

RFs for SA

Prosthetic implant | Damaged joints, e.g. RA

Aetiology of SA

Infected joint replacement most common | Metaphyseal septic focus can lead to either septic arthritis/OM

SA most common organisms

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

Pathology of SA

Acute synovitis w. purulent joint effusion | Articular cartilage attacked by bacterial toxin and cellular enzymes --> complete destruction of articular cartilage

Sequlae of SA

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

Neonatal presentation of SA

Irritability, resistant to movement, ill

Child/adult presentation og SA

``` Acute pain in single joint Reluctance to move joint Fever and tachycardia Tenderness Joint swelling/redness/hot ``` In adults often knee

Ix SA

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

Differentials SA`

``` Acute OM Trauma Irritable joint Haemophilia Rheumatic fever Gout ```

Mx SA

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

TB classification

Extra-articular Intra-articular Vertebral body

CF TB

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

Pathology TB

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

CF spinal TB

Little pain | Present with kyphosis/abscess

Diagnosis of TB

Long Hx affecting single joint | Marked thickening of synovium, marked muscle wasting, periarticular osteoporosis

Ix TB

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

Differentials TB

``` TS Monoarticular RA Haemorrhagic arthritis Pyogenic arthritis Tumour ```

Mx TB

2 months - rifampicin, isoniazid, ethambutol 6-12m: rifampicin, isoniazid Rest, splintage, op drainage sometimes