septic arthritis

definition

·      inflammation of a joint caused by pus-forming organisms

incidence

·      occurs in all age groups

·      primarily seen in children

·      50% in children < age 3

·      30% in children < age 2

·      equal sex incidence

·      can involve any joint (and multiple joints)

·      infants

·      usually involves hip

·      children

·      most commonly affects knee

·      adults

·      can involve hip, knee, elbow, shoulder and ankle

·      IV drug users

·      may involve sterno-clavicular and sacro-iliac joints

pathogenesis
Source

·      bacteria gain access to joint by one of three routes

Haematogenous

·      distant focus

·      skin infection

·      URTI

·      ear infection

·      IV drug abuse

·      seeds synovial membrane via blood stream

Direct extension

Osteomyelitis

·      most common route in neonates and children

·      from adjacent focus of osteomyelitis

·      more common where metaphysis is intra-articular

·      proximal femoral and proximal humeral metaphysis are intracapsular structures

·      portion of distal femoral metaphyses is intracapsular

·      no intra-articular periosteal lining around metaphysis

·      if metaphyseal osteomyelitis develops, pus can

·      enter joint via transphyseal vessels (neonates)

·      escape through haversian and Volkmann's canals into joint space (children)

Soft tissue

·      from soft tissue infection

Direct innoculation

·      accidental

·      penetrating injury

·      iatrogenic

·      joint injection or aspiration

·      surgical procedure

·      inadvertent joint penetration (eg. neonatal femoral puncture)

Predisposition

·      depends on two factors

General host factors

·      immune deficiency

·      malignancy

·      immunosuppression

·      prematurity

·      chronic illness

·      rheumatoid arthritis, diabetes, SLE, chronic renal failure, alcoholism

Local joint factors

·      previous joint trauma

·      rheumatoid arthritis

·      chronic hyperaemia

·      inflammatory exudate

·      local steroid injection

·      immune deficiency

·      immunosuppressive agents

·      crystal arthropathy

aetiology

·      may be community-acquired or hospital-acquired

·      organisms vary according to age

·      in 1/4 to 1/3 of cases, the organism is not identified

·      most common organism in all cases is Staph aureus

Neonates (< 1 month)

Hospital-acquired

·      common (60%)

·      most common organisms are

·      gram negatives

·      Candida

·      Staph aureus

·      group B strep

·      usually predisposing factors (prematurity, premature rupture, respiratory distress)

·      contiguous osteomyelitis common (70%)

·      high mortality (30%)

Community-acquired

·      most common organisms

·      Staph aureus

·      group B strep

·      child usually well

·      contiguous osteomyelitis also common (66%)

·      mortality low

Infants and children <3 yrs

·      after Staph aureus, Haemophilus influenzae is predominant organism

Children >3 yrs

·      more adult picture

Adults

·      most common organisms are

·      Staph aureus

·      streptococcus

·      gram-negatives

·      in IV drug abuse, see

·      Pseudomonas

·      Klebsiella

·      Serratia

pathology

·      initially, synovium becomes oedematous and hyperaemic

·      increased amount of synovial fluid produced

·      synovial fluid cloudy

·      within few days, frank pus accumulates

·      cartilage destruction begins

·      starts at areas of contact with opposing surface

·      synovial membrane replaced by granulation tissue

·      fibrin clots and forms pockets of pus and adhesions that limit movement

·      if uncontrolled, fibrous or bony ankylosis of the joint results

·      if physis is intracapsular, it may be destroyed and growth may be impeded

·      increased intracapsular pressure in the hip may lead to

·      subluxation or dislocation

·      avascular necrosis of the femoral head

Cartilage destruction

Proteoglycans

·      first step is loss of proteoglycans

·      due to

·      decreased movement with lack of nutrition

·      lysosomal enzymes released from cartilage

·      lysosomal enzymes released by inflammatory cells

·      extracellular proteolytic enzymes produced by bacteria

·      plasmin-plasminogen activated by staphylokinase

Collagen

·      second step is loss of collagen

·      due to release of collagenases

Fragmentation

·      third step due to mechanical fragmentation of cartilage

clinical picture
Infant

·      may develop in infant who is already unwell with septicaemia and other focal infections

·      diagnosis usually delayed

Symptoms

·      history of antecedent infection (eg. umbilical sepsis)

·      poor feeding

·      irritability

·      failure to thrive

·      low-grade fever

·      constitutional features may be minimal or absent

Signs

·      affected joint warm and swollen

·      more easy to detect if joint subcutaneous

·      with hip, thigh and buttock may be swollen

·      earliest sign is loss of active movement

·      muscle spasm develops and limb held in position of least intra-articular pressure

·      hip abducted 45o, flexed 15o and externally rotated 15o

·      knee flexed 20o

·      palpation of joint and attempted movement of affected limb causes infant to cry

Child

Symptoms

·      often there is history of recent injury or antecedent infection (URTI, boil, middle ear infection)

·      acute onset of pain and fever

·      irritability and anorexia

Signs

·      joint warm and swollen

·      unwilling to weight-bear (if lower limb)

·      joint held rigidly in position of minimal intra-articular pressure

·      even slightest movement not permitted

investigations
Laboratory

ESR

·      almost always raised

·      typically 100 and usually over 40

·      not reliable in

·      first 36-48 hours

·      neonate

·      patient on steroids

·      not a good measure of treatment in first week

·      fall lags behind resolution of sepsis

WBC

·      often normal (>10 000 in only 50%)

·      may have polymorphonuclear leukocytosis

Blood culture

·      positive in 50% of patients

Aspiration

·      essential investigation

·      should be done as soon as diagnosis suspected

·      in infant with suspected septic arthritis of hip, should proceed to arthrotomy without aspiration if diagnosis likely because

·      need GA for aspiration

·      aspiration difficult to perform

·      may cause articular damage with needle

Technique

·      strict aseptic technique

·      preferably in theatre with general anaesthetic

·      use wide-bore needle with stylet

·      collect fluid in

·      plain tube for culture

·      EDTA tube for microscopy and cell count

introduce saline if dry tap

Hip

·      use image intensifier and perform arthrogram at end

·      palpate femoral artery in line with inguinal ligament

·      insert needle 2.5 cm lateral and 2.5 cm distal to this point

·      aim needle at 45o angle to skin medially and proximally

Knee

·      insert needle on lateral side at level of superior pole of patella

Elbow

·      flex elbow

·      insert needle on posterior aspect just lateral to olecranon

Shoulder

·      insert needle anteriorly half way between coracoid process and antero-lateral edge of acromion

Ankle

·      insert needle 2.5 cm proximal and 1.3 cm medial to tip of lateral malleolus

Characteristics of synovial fluid

·      appearance

·      yellow or grey and opaque

·      WCC

·      usually > 50 000

·      often > 100 000

·      cells

·      neutrophils usually > 75%

·      often > 90%

·      glucose

·      usually less than blood glucose

·      organisms

·      seen in 30%

·      crystals

·      may be present

·      septic arthritis and crystal arthopathy may occur simultaneously

·      infection leads to decreased pH and decreased solubility of urate

·      culture

·      positive in 60%

X-ray

·      may only show soft-tissue swelling

·      after one week, may see narrowing of joint space from loss of articular cartilage

·      later, subchondral osteoporosis and bone destruction seen

Hip in infancy

·      widening of joint space

·      subluxation or dislocation of hip joint

·      may see evidence of primary focus of osteomyelitis

·      metaphseal rarefaction and periosteal new bone formation

·      may be erosion of ossific nucleus of epiphysis

Bone scan

·      entire area shows increased uptake

Hip in infancy

·      focal metaphyseal uptake if associated osteomyelitis

·      femoral head may be cold (indicates early avascular necrosis)

Ultrasound

Hip in infancy

·      confirms fluid in joint

differential diagnosis
Infants and children

Acute osteomyelitis

·      common in infants and children

·      difficult to differentiate from adjoining sympathetic effusion

·      usually less restriction of motion

·      occur together in 70% in infants

Cellulitis

·      more local skin redness and oedema

·      lymphadenopathy

Transient synovitis

·      in hip in child

·      not as severe loss of movement

·      no constitutional symptoms

·      ESR normal

Juvenile rheumatoid arthritis

·      onset usually more gradual

·      fewer systemic features

·      more movement possible in joint

Trauma

·      epiphyseal injuries in children may be difficult to differentiate

·      no evidence of septicaemia

Perthes disease

·      restriction of ROM

·      no septic features

Haemophilia

·      joint pain may be first presentation of haemophilia

Adults

Crystal arthropathy

·      in adults, esp. in knee

·      similar clinical picture

Gout

·      uric acid often raised

·      may see peri-articular punched-out lesions

Chondrocalcinosis

·      may see meniscal and articular calcification

treatment
Antibiotics

Initiation

·      commence immediately diagnosis assumed

·      collect aspirate and blood for cultures first

·      do not wait for culture and sensitivity reports

Choice

·      bacteriocidal rather than bacteriostatic agent

·      choice may be guided by Gram stain

Gram-positive cocci (staph and strep)

·      use flucloxacillin

·      2g q6h in adult and 40 mg/kg/dose (max 2g) q6h in child

·      if sensitive, use cephalothin

·      same dose as flucloxacillin

·      if severely sensitive (life-threatening anaphylaxis), use clindamycin

·      600 mg q8h in adult

·      if MRSA on culture, switch to vancomycin

·      1g q12h in adult and 20 mg/kg/dose q12h in child

·      if penicillin-sensitive on culture, switch to penicillin G

·      1.2g q4h in adult and 25 mg/kg/dose q4h in child

Gram-negative cocci in child (Haemophilus)

·      use ceftriaxone

·      25 mg/kg/dose q12h

·      alternatively can use amoxycillin and chloramphenicol

·      amoxycillin 400 mg/kg/day in 4 doses

·      chloramphenicol 100 mg/kg/day in 4 doses

Gram-negative cocci in adult (gonococcus)

·      use penicillin

Gram-negative bacilli

·      use ceftriaxone

·      1g q12h in adult and 25 mg/kg/dose q12h in child

·      alternatively, use gentamicin 5 mg/kg/day in 1 dose

No organisms on Gram stain

·      in children < 3 yrs, use flucloxacillin and ceftriaxone

·      in older children and adults, use flucloxacillin

·      if immunocompromised, add ceftriaxone

Route and duration

·      use IV until systemic toxicity and local swelling subside (1 to 2 weeks)

·      then switch to oral

·      total duration is empirical but most suggest 6 weeks

·      do not use high-dose intra-articular antibiotics

·      ineffective

·      may cause chemical synovitis and increase articular destruction

Drainage

·      debridement is of paramount importance - SURGICAL EMERGENCY

Aspiration vs surgical drainage

·      most agree that surgical drainage of the hip is indicated

·      for more superficial joints, there is controversy

·      rheumatologists and paediatricians tend to favour repeated aspiration

·      surgeons tend to prefer surgical drainage

Technique

·      perform arthrotomy (or arthroscopy) of joint

·      excise part of capsule and synovium

·      copiously wash out purulent material

·      leave joint open and close skin

Hip

1.   Anterior approach

·      in form of Smith-Peterson approach

·      advantage that no muscle is cut

·      commonly used in children

·      7.5 cm oblique incision centred 1 cm below ASIS

·      angled inferior and medial

·      expose and separate sartorius medially and tensor fascia lata and vastus lateralis laterally

·      identify lateral border of rectus abdominus and retract it medially

·      incise exposed capsule

2.   Posterior approach

·      in form of Ober approach

·      advantage of gravitational drainage

·      commonly used in adults

·      oblique incision in line of femoral neck

·      from 2.5 cm distal to greater trochanter to PSIS

·      split gluteus maximus in line of fibres

·      ligate gluteal vessels

·      identify and protect sciatic nerve at medial angle of incision

·      split and retract external rotators

·      if necessary, divide external rotators at insertions on greater trochanter

·      incise distended capsule

Knee

·      medial parapatellar arthrotomy

·      arthroscopy may be method of choice

Shoulder

·      anterior delto-pectoral approach

·      incision in delto-pectoral groove

·      split deltoid and pectoralis, preserving cephalic vein

·      retract short head of biceps and coracobrachialis  medially

·      externally rotate arm and divide conjoined subscapularis and capsule vertically

Elbow

·      lateral approach

·      7.5 cm longitudinal incision over lateral epicondyle

·      separate triceps and ECRL

·      expose and incise capsule

Ankle

·      anterolateral approach

·      7.5 cm incision over joint lateral to EDC and peroneus tertius tendons

·      expose and incise capsule

Rest joint

·      splint joint initially in position of function

·      hip in abduction and neutral rotation in skin traction or hip spica in infant

·      knee in full extension in backslab

·      ankle plantigrade in backslab

·      elbow in 90o flexion in backslab

·      shoulder in neutral in Velpeau sling

·      start passive and active-assisted exercises after acute phase subsides (48 hrs)

·      use CPM for knee

·      for lower limb, use protected weight-bearing until full pain-free ROM

prognosis
Prognostic factors

Treatment delay

·      most important prognostic factor

Joint involved

·      poorer if hip involved

Associated osteomyelitis

·      prognosis poorer

Organism

·      poorer with Staph aureus or multiple organisms

Age of patient

·      worse for infants

·      hip more often involved

·      delay in diagnosis

Complications

·      joint destruction with ankylosis

Hip in infancy

·      related to delay to treatment

·      subluxation and dislocation of hip

·      destruction of capital femoral epiphysis

·      local growth disturbance

·      coxa magna

·      leg length discrepancy

Special conditions

postinfectious arthritis

·      occurs in

·      meningococcal arthritis (most commonly)

·      streptococcal arthritis (occasionally)

·      clinical septic arthritis that develops 5-7 days after commencement of treatment

·      represents Arthus reaction

·      due to interaction of newly produced circulating antibodies and bacterial antigens in synovium

·      interaction produces immune complexes and inflammatory response