Septic arthritis Inflammatory joint disease caused by bacterial, viral or fungal infection.

Route of infection dissemination of pathogens via Blood (most common) Direct from adjacent site Acute osteomylitic focus Adjacent soft tissue infection Penetrating trauma Iatrogenic means Etiology S. aureus H. influenzae (children < 3 y.) G-ve bacilli (E. coli) Streptococci

Pathology Acute synovitis with a purulent joint effusion Synovial membrane becomes edematous, swollen, hyperemic & produces increase amount of cloudy exudates contains leukocytes and bacteria As infection spread through the joint, articular cartilage is destroyed by bacterial and cellular enzymes. If the infection is not arrested the cartilage may be completely destroyed. Pus may burst out of the joint to form abscesses and sinuses. The joint may be become pathologically dislocated.

With healing there will be: Complete resolution and return to normal. Partial loss of cartilage and fibrosis. Bone ankylosis Bone destruction and permanent deformity.

Clinical presentation Acute pain and swelling in a single large joint Commonly the hip in children and the knee in adults. The most commonly involved joint Knee (50%) Hip (20%) Shoulder (8%) Ankle & wrists (7%) Interphalangeal, sternoclavicular & sacroiliac joints (1-4%)

Newborns or infants The emphasis is on septicemia rather than joint pain. Irritability, Fever, refuses to feed, rapid pulse. Pseudoparalysis (unable to move the limb with the infected joint). Cries when infected joint is moved (diaper changing) Infection is usually suspected, but it could be anywhere so the joints should be carefully felt and moved to elicit the local signs of warmth, tenderness and resistance to movement. Umbilical cord or the site of injection should be examined for possible source of infection. If the baby is distressed and wont move his/her leg think of hip infection.

Children: Adult: Fever Acute pain in single large joint. The joint is swollen, warm and tender. Pseudoparesis (all movements are restricted due to muscle spasm). Adult: Low-grade fever Intense joint pain Joint swelling, redness Unable to move the limb with the infected joint

Physical examination Signs of inflammation: joint swelling, warmth, tenderness and erythema. Decreased or absent rang of motion. Joint orientation as to minimize pain (position of comfort): Hip: abducted, flexed and externally rotated. Knee, ankle and elbow: partially flexed. Shoulder: abducted and internally rotated.

Investigation Lab studies: The diagnosis can usually be confirmed by joint aspiration and immediate microbiological investigation of the fluid. Leucocytosis, elevated ESR & CRP (suggestive but not diagnostic). Ask for: gram stain, culture, leukocyte count with differential, and crystal examination Leukocyte count generally >75,000/µL, with a predominance of neutrophils >75% in synovial fluid aspiration. Gram stain are positive in approximately 75% of patients with staphylococcal infections; however, results are positive in only 50% of patients with gram-negative infections. Crystal examination to exclude crystal-induced arthritis (may coexist) Synovial fluid glucose, protein, & lactic acid concentration not specific.

RA <50,000 wbc count

Imaging studies X-ray US Detecting joint effusions generated by septic arthritis. Define the extent of septic arthritis & guide treatment. Differentiate septic arthritis from other conditions (soft tissue abscesses, tenosynovitis) Radio-isotope bone scan Increase uptake (help in difficult site as sacroiliac & sternoclavicular joints) CT scan (sternoclavicular or sacroiliac joint infections) MRI, most useful in assessing the presence of periarticular osteomyelitis as a causative mechanism.

Plain x-ray The appearance of significant x-ray findings depends upon the duration and virulence of infection. Findings are generally nonspecific: Soft tissue swelling Widening of the joint space (effusion) Periarticular osteoporosis during the 1st 2 w. Later, when the articular cartilage is attacked Narrowed joint space (persistent subluxation, destructive arthritis).

Septic arthritis of the hip following group B strep psoas abscess

Septic arthritis of the ankle

Differential diagnosis Osteomyelitis: near a joint may be indistinguishable from septic arthritis ;the safest is to assume that both are present. Acute haemarthrosis: either post-traumatic or due to a haemophilic bleed ,can closely resemble infection. The history is helpful and joint aspiration will resolve any doubt. Transient synovitis (irritable joint) in children: symptoms & signs are less acute. Gout and pseudogout in adults: aspirated fluid may look turbid but the presence of urate or pyrophosphate crystals will confirm the diagnosis. Rheumatic fever

Complication Dislocation: a tense effusion may cause dislocation Epiphyseal destruction: in neglected infants the largely cartilaginous epiphysis may be destroyed ,leaving an unstable pseudarthrosis. Growth disturbance: physeal damage may result in shortening or deformity Ankylosis: if articular cartilage is eroded healing may lead to ankylosis Secondary osteoarthritis Osteomyleitis/abcess/sinus

Treatment Aspirate the joint and examine the fluid, then treat. Analgesics and splinting of the involved joint in the position of maximal comfort alleviate pain. Fluid replacement and nutritional support may be required. Treat any infection or coexisting medical conditions. Blood sample & culture IV antibiotics Flucloxacillin (G+ve) 3rd generation cephalosporin (G+ve & G-ve). Ampicillin: children <4y. (suspicion of H.Infl)

Drainage Indication of Surgical Drainage: Joints that do not respond to antimicrobial therapy and daily arthrocentesis. Any joint with limited accessibility, including the sternoclavicular or the hip joint. Patients with underlying disease, including diabetes, RA, immunosuppression, or other systemic symptoms, should be treated more aggressively with earlier surgical intervention.

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