SEPTIC ARTHRITIS   Pyogenic infection of a joint space. It is a particularly serious infection of in children, because of potential for complete damage to joint cartilage and long term sequalae Sites Septic arthritis affects the hip and the knee most commonly, although the elbow, ankle, and shoulder are often involved. Smaller distal joints are less likely to be affected by septic arthritis than are larger proximal ones. Age  Septic arthritis can occur in those of any age, but it predominantly affects young children. In children, septic arthritis most commonly occurs in those younger than 3 years. Septic arthritis is uncommon from age 3 years to adolescence. The incidence increases during adolescence with the appearance of gonococcal infections. Etiology §  Staphylococcus aureus-most common §  Streptococcus pneumoniae, group B streptococci, Gonococcus species §  Escherichia coli §  Haemophilus species especially in infants §  Klebsiella species §  Gonococcus §  Pseudomonas species §  Candida species Mechanisms of infection 1. Blood spread from a distant site-Most common 2.Direct invasion through §  Penetrating wound §  Intra-articular injection §  arthroscopy §  Direct spread from an adjacent bone abscess, osteomyelitis or cellulitis 2nd most common cause of septic arthritis is spread from adjacent osteomyelitis. In anatomic locations where the metaphysis of the bone is intraarticular, such as the hip and the shoulder, a metaphyseal focus of osteomyelitis may penetrate  Predisposing Conditions -Rheumatoid arthritis -IV drug abuse -Immunosuppression - Chronic debilitating disorders; Immunosuppressive drug therapy; AIDS -Presence of joint prosthesis -Arthroscopy  Pathophysiology The usual trigger is a haematogenous infection which settles in the synovial membrane. There is an acute inflammatory reaction - acute synovitis, with a serous then seropurulent exudate and an increase in synovial fluid and joint pressure. As pus appears in the joint, articular cartilage is eroded and destroyed partly by enzymes released from synovium, inflammatory cells and pus. Once the articular cartilage is lost, it cannot be replaced with further growth because it has little or no ability to heal or remodel. 2. Ultrasound Joint effusion evaluation and aspiration may be done. In children the joint 'space' may seem to be widened (because of the fluid in the joint) & there may be slight sublaxation of the joint. With E. coli infections there is sometimes gas in the joint. Narrowing or irregularity of the joint space are late feature 3.MRI Incase of complications with soft tissue involvement –menisci injury or spread to cause oseomyelitis. Evaluation of epipyseal necrosis in children Differential diagnosis 1.Acute osteomyelitis 2.Gout & pseudogout 3.Trauma - Traumatic synovitis or haemarthrosis 4.Haemophilic bleed 5.Acute Rheumatic fever - typically pain flits from joint to joint 6.Gaucher's disease - Presents as acute joint pain & fever without any organism being found ('pseudo-osteitis') 7.Bursitis and tenosynovitis 8.Sickle cell disease in crises MANAGEMENT To prevent irreparable damage to the articular cartilage, prompt diagnosis and treatment are mandatory. Principles of management 1.Immobilization of the joint to control pain 2.Administration of appropriate antimicrobial therapy 3. Adequate and timely drainage of the infected synovial fluid. Immobilization and supportive management a) NSAIDS -Analgesics for pain and reduce inflammation b) IV fluids for dehydration c) Rest the joint on a splint -hip infection, the joint should be abducted & 30° flexed, on traction; §  To reduce pain §  To prevent dislocation §  To keep the synovial cavity open to allow circulation §  In children;To prevent slipping of the upper femoral epiphysis and strengthen the perichondral ring d)Empirical antibiotic therapy After aspiration of joint for microscopy ,culture and sensitivity and drawing of blood for blood cultures then empirical antibiotics started: Less than 4years - Augmentin or 3rd generation cephalosporins-cover the bram negatives and staph, aureus Older children & Adults - Flucloxacillin & Fusidic acid IV for 2-7days & then orally for another 3wks In children, give cod-liver oil which reduces inflammation by supplying Omega 3 reducing the formation of arachidonic acid necessary for the formation of prostaglandins that mediate inflammation.

In infants, the entire epiphysis, which is still largely cartilaginous, may be severely damaged; in older children, vascular occlusion may lead to necrosis of the epiphyseal bone. The continued swelling of the joint may cause it to dislocate. Dislocation is particularly common at the hip in infants. In children, necrosis of the epiphysis may also include necrosis of the reserve zone of the physis, with cessation of growth In adults, the effects are usually confined to the articular cartilage, but in the late cases, there may be extensive erosion due to synovial proliferation & growth. If the infection goes untreated, it will spread to the underlying bone or burst out of the joint to form abscesses & sinuses. In adults untreated septic arthritis may cause: 1.Partial loss of articular cartilage & fibrosis of the joint with pain and stiffness. 2.Loss of articular cartilage & bony ankylosis 3.Bone destruction & permanent deformity of the joint 4. Extend into the underlying bone, leading to osteomyelitis. 5. Extracapsular infectious complications such as myositis and abscess formation in adjacent soft tissues. Clinical presentation 1.Acute painful joint 2.Diffuse swelling of the joint 3.The overlying skin looks red 4.Local warmth & marked tenderness 5.Swinging fever 6.Rapid pulse 7.Reluctance to move the limb ('pseudoparesis') - All movements are restricted, & often completely abolished, by pain & spasm Investigations Gold standard   Joint aspiration m/c/s - Leukocyte counts >50,000/ml Normal synovial fluid leukocyte count - <300/ml Non-infective inflammatory disorders - >10,000/ml Laboratory 1.FHG - ↑WBC –neutrophilia 2.ESR and C-reactive proteins elevated 3.Blood culture - May be positive Imaging 1.Plain X-ray Early disease show soft tissue swelling around the joint and a widened joint space from joint effusion. Displacement of adjacent fat pads may be present, especially in infants and children. With progression of the disease, plain films reveal joint-space narrowing as articular cartilage is destroyed. Loss of visualization of the white cortical line over large areas of the joint surface soon ensues as bone destruction begins to develop. Plain film findings of superimposed osteomyelitis may develop (periosteal reaction, bone destruction, sequestrum formation). Surgical intervention-Arthrotomy If there is frank pus in the joint or if the hip joint of a child is involved with septic arthritis, immediate surgery is indicated. The joint must be surgically decompressed. Pus and fibrinous debris must be removed. In these instances, septic arthritis is a true orthopedic emergency Under general anaesthesia the joint is opened through a small incision, drained & washed out with physiological saline. A small catheter is left in place & the wound is closed; suction-irrigation is continued for another 2-3days. Surgery -In very young infants -When the hip is involved (Joint is opened from behind) -If the aspirated pus is very thick For knee, arthroscopic debridement from the lateral aspect & copious irrigation may be equally effective Older children with early septic arthritis (symptoms for <3days) involving any joint except the hip - Repeated closed aspiration of the joint; however, if there is no improvement within 48hrs, open drainage will be necessary. Post-op; -Intact articular cartilage - Physiotherapy -Destroyed articular cartilage - The joint is splinted in the optimum position awaiting ankylosis (stiffness or fixation of a joint by disease or surgery