Joint and Bone Infections

Joint and Bone Infections

Septic Arthritis

·        Presentation: systemic illness with fever, usually one joint (knee most common), swelling, effusion, warmth, markedly reduced movement of the affected joint, and very painful to move (cf adjacent osteomyelitis ® some pain only). Hip and shoulder have less swelling

·        In neonates, may overlap with acute haematogenous osteomyelitis

·        Risk factors: diabetes, recurrent steroid injections, systemic steroids, alcoholic liver disease, immunosuppression

·        Differential:

o  Gout and pseudogout

o  Haemarthrosis

o  Acute osteomyelitis

o  Acute traumatic arthritis

·        Pathogenesis:

o  From haematogenous spread or extension of osteomyelitis, often following distant infection. Also following penetrating injury

o  WBC enzymes rapidly erode articular cartilage ® surgical emergency: empiric antibiotics and rapid drainage. Urgent – can destroy a joint in 24 hours. In neonates/kids can damage growth plate ® growth disturbance

o  S. Aureus, also S pneumoniae and S pyogenes. In high-risk groups, M Tb and Candida. Neonates consider S agalactiae, Haemophilus and N gonorrhoea (did they have bacterial conjunctivitis soon after birth?). Pseudomonas from foot wound.

o  Tb arthritis: usually haematogenous spread from lungs to hips (kids), knees (adults) or spine. X-ray shows marginal erosions and destruction of sub-chondral bone (like Rheumatoid – but different distribution). Have granulomas (except in AIDS). Histology: Granulomas are pink, cf lymphoid aggregates in Rheumatoid that are blue

·        Investigations:

o  Joint aspiration (arthrocentesis: opaque fluid with WBC > 50,000/ml)

o  FBC, ESR, CRP, blood cultures, plain Xray, US (for detection effusion)

o  Xray delays rather than establishes the diagnosis

·        Management:

o  Flucloxacillin: for staph aureus, but also covers S pneumonia, S pyogenes, S agalactiae

o  If neonate:

§  And unimmunised consider H. Influenzae: cefuroxime or cefotaxime

§  Consider G –ive: gentamycin

o  Arthroscopic washout

o  Initial splinting for pain relief, but then encourage mobility

o  If there is a joint prosthesis, revision may be necessary

·        Complications due to delayed diagnosis:

o   Joint degeneration, joint dislocation 

o   Damage to the growth plate ® growth arrest

Osteomyelitis

·        Common in low socio-economic and warmer weather

·        May follow minor trauma with or without infection elsewhere in body

·        Acute haematogenous osteomyelitis:

o   Presentation:

§  Early: short, febrile illness, bone pain, metaphyseal tenderness (point tenderness)

§  Late: Swelling/erythema (suggest abscess). Cellulitis. Adjacent joints sore but some movement still possible

§  Vascular supply to bone is compromised and infection spreads to surrounding soft tissue

o   Differential diagnosis:

§  Septic arthritis

§  Cellulitis

§  Trauma (Facture)

§  Tumour

o   Aetiology:

§  Trauma/surgery ® direct introduction of bacteria

§  Direct extension from infective site: eg dental infection ® jaw, diabetic foot ® bones of foot

§  Haematogenous seeding:

·        Commonest site in children is metaphysis of the long bones. Femur and tibia account for > ½ all cases (especially around knee joint). Epiphyseal growth plate acts as a barrier to the spread of infection to the joint. May spread through Haversian and Volkmann‟s canal system to form a subperiosteal abscess (requires drainage)

·        In adults, haematological spread less common. Tends to affect subperiosteal corticies of long bones. Also cancellous bone of vertebral bodies, may ® compression fracture

·        Eg: sluggish blood flow ® easy thrombosis following trauma ® predisposes to infection (esp staph aureus)

o   Pathology: Inflammatory response ® oedema ® compromise vascular supply ® necrosis ® spread of infection through cortices ® pus under periosteum ® shearing of periosteum ® further disruption to blood vessels

o   Causative organisms:

§  Under one year: staph aureus, strep agalactiae, E coli.  May be non-specific illness

§  Children: staph aureus, strep pyogenes, H influenzae 

§  Adults: staph aureus, staph epidermis and G negatives (E coli, salmonella and pseudomonas from foot wounds)

§  M. Tb and Candida in high risk groups

o   Complications:

§  Spread of infection ® septicaemia, joint infection

§  Fracture, abscess formation 

§  ® Chronic osteomyelitis in 5 – 20% of cases

·        Subacute osteomyelitis: Focal rather than systemic response to infection. Xray shows bone destruction. Differential includes bone tumour and stress fracture

·        Chronic osteomyelitis:

o   Usually delayed or inadequate treatment.

o   Pain, swelling +/- discharging sinuses. 

o   Xray: destruction, with sequestrum (areas if necrotic bone which can‟t be resorbed) harbouring bacteria and involucrum (formed from periosteum raised over an abscess). Brodie‟s abscess: abscess surrounded by sclerotic bone due to organisms of low virulence 

o   Treatment: sequestrum must be removed, may require repeated surgery. Poor penetration of antibiotics

o   Complications:

§  Persistently discharging sinus

§  Chronic ill health

§  Pathological fractures/deformities 

§  Malignant change ® SCC

·        Investigations:

o  Blood: FBC, ESR, CRP, Blood cultures (+ive in 50%)

o  Imagining:

§  Plain films: no changes until day 10

§  US: subperiosteal abscesses

§  Bone scan: very sensitive but not specific

§  MRI: very sensitive but expensive

§  CT: good for detecting degree of bone destruction

·        Treatment: 

o  High dose IV antibiotics for at least 2 – 4 days (for children, Flucloxacillin 50 mg/kg/6 hourly, max 2 g), followed by 3 – 4 weeks of oral therapy 

o  Surgery to decompress and remove necrotic bone if late or failed medical treatment, or subperiosteal abscess drainage

·        Specific presentations:

o  Osteomyelitis of the calcaneum: infection 5 – 10 days after puncture wound.  P aeruginosa

o  Discitis: inflammation of the lumber disc, usually < 8 years 

o   Pelvic osteomyelitis: pain referred to the abdomen, buttock or leg.  S aureus.  Bone scan diagnostic

o  Tb Osteomyelitis: rare in developed world.  Occurs in 1-3% of patients with pulmonary Tb. 

o   Insidious. After months: pain on movement, fever, night sweats, weight loss. Destructive. If lumber or thoracic vertebrae may ® hunchback deformity

Pyogenic infections of the hand

·        Usually history of trauma

·        Paronychia: common infection of periungual tissues, usually by Staph Aureus

·        Felon: deep infection of the pad of the finger.  Usually Staph aureus following puncture wound

·        Cellulitis: Strep Pyogenes infection

·        Suppurative flexor tenosynovitis:

o  Infection of flexor tendon sheaths 

o  Presentation: Swollen finger with painful motion. Symmetrical swelling, tenderness, erythema along tendon sheath. Semi flexed posture and severe pain on passive extension of DIP joint

o  Signs: crepitus, erythema, vesicle formation, colour, pain, puss

o  Tests:

§  Culture of puss, blood culture, FBC

§  X-ray to rule out foreign body, air in tissue or joint, associated fracture

o  Treatment: irrigate, leave wound open and dress after swelling has decreased, antibiotics, splint

·        Atypical infections:

o  Herpes infections of the thumb and fingers (eg Whitlow‟s lesions)

o  Fungal infections: more indolent.  Sporotrichosis common