ACUTE SUPPURATIVE ARTHRITISA joint can become infected by: (1) direct invasion through a penetrating wound, intra-articular injection or arthroscopy; (2) direct spread from an adjacent bone abscess; or (3) blood spread from a distant site. In infants it is often difcult to tell whether the infection started in the metaphyseal bone and spread to the joint or vice versa. In practice it hardly matters and in advanced cases it should be assumed that the entire joint and the adjacent bone ends are involved. The causal organism is usually Staphylococcus aureus; however, in children between 1 and 4 years old, Haemophilus inuenzae is an important pathogen unless they have been vaccinated against this organ-ism. Occasionally other microbes, such as Streptococcus, Escherichia coli and Proteus, are encountered. Predisposing conditions are rheumatoid arthritis, chronic debilitating disorders, intravenous drug abuse, immunosuppressive drug therapy and acquired immune deciency syndrome (AIDS).Pathology The usual trigger is a haematogenous infection which settles in the synovial membrane; there is an acute inammatory reaction with a serous or seropurulent exudate and an increase in synovial uid. As pus appears in the joint, articular cartilage is eroded and destroyed, partly by bacterial enzymes and partly by proteolytic enzymes released from synovial cells, inammatory cells and pus. 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. In adults the effects are usually conned to the articular cartilage, but in late cases there may be extensive erosion due to synovial proliferation and ingrowth.If the infection goes untreated, it will spread to the underlying bone or burst out of the joint to form abscesses and sinuses. With healing there may be: (1) complete resolution and a return to normal; (2) partial loss of articular cartilage and brosis of the joint; (3) loss of articular cartilage and bony ankylosis; or (4) bone destruction and permanent deformity of the joint.Clinical features The clinical features differ somewhat according to the age of the patient. In newborn infants the emphasis is on septicaemia rather than joint pain. The baby is irritable and refuses to feed; there is a rapid pulse and sometimes a fever. Infection is often suspected, but it could be anywhere! The joints should be carefully felt and moved to elicit the local signs of warmth, tenderness and resistance to movement. The umbilical cord should be examined for a source of infection. An inamed intravenous infusion site should always excite suspicion. The babys chest, spine and abdomen should be carefully examined to exclude other sites of infection.Special care should be taken not to miss a concomitantosteomyelitis in an adjacent bone end.In children the usual features are acute pain in a single large joint (commonly the hip or the knee) and reluctance to move the limb (pseudoparesis). The child is ill, with a rapid pulse and a swinging fever. The overlying skin looks red and in a supercial joints welling may be obvious. There is local warmth and marked tenderness. All movements are restricted, and often completely abolished, by pain and spasm. It is essential to look for a source of infection a septic toe, a boil or a discharge from the ear. In adults it is often a supercial joint (knee, wrist, a nger, ankle or toe) that is painful, swollen and inamed. There is warmth and marked local tender-ness, and movements are restricted. The patient should be questioned and examined for evidence of gonococcal infection or drug abuse. Patients with rheumatoid arthritis, and especially those on corticosteroid treatment, may develop a silent joint infection. Suspicion may be aroused by an unexplained deterioration in the patients general condition; every joint should be carefully examined.ImagingUltrasonography is the most reliable method for revealing a joint effusion in early cases. Both hips should be examined for comparison. Widening of the space between capsule and bone of more than 2 mm is indicative of an effusion, which may be echofree (perhaps a transient synovitis) or positively echogenic (more likely septic arthritis). X-ray examination is usually normal early on but signs to be watched for are soft-tissue swelling, loss of tissue planes, widening of the radiographic joint space and slight subluxation (because of uid in the joint). With E. coli infections there is sometimes gas in the joint. Narrowing and irregularity of the joint space are late features.MRI and radionuclide imaging are helpful in diagnosing arthritis in obscure sites such as the sacroiliac and sterno clavicular joints.Investigations The white cell count and ESR are raised and blood culture may be positive. However, special investigation take time and it is much quicker (and usually more re-liable) to aspirate the joint and examine the uid. It maybe frankly purulent but beware! In early cases the uid may look clear. A white cell count and Gram stain should be carried out immediately: the normal synovial uid leucocyte count is under 300 per mL; it may be over 10 000 per mL in non-infective inammatory dis-orders, but counts of over 50 000 per mL are highly suggestive of sepsis. Gram-positive cocci are probably S. aureus; Gram-negative cocci are either H. inuenzae or Kingella kingae (in children) or Gonococcus (in adults). Samples of uid are also sent for full micro -biological examination and tests for antibiotic sensitivity. Differential diagnosis Acute osteomyelitis In young children, osteomyelitismay be indistinguishable from septic arthritis; often one must assume that both are present. Other types of infectionPsoas abscess and local infectionof the pelvis must be kept in mind. Systemic featureswill obviously be the same as those of septic arthritis.Trauma Traumatic synovitis or haemarthrosis may beassociated with acute pain and swelling. A history of injury does not exclude infection. Diagnosis may remain in doubt until the joint is aspirated. Irritable joint At the onset the joint is painful and lackssome movement, but the child is not really ill and there are no signs of infection. Ultrasonography may help to distinguish septic arthritis from transient synovitis.Haemophilic bleedAn acute haemarthrosis closelyresembles septic arthritis. The history is usually conclusive, but aspiration will resolve any doubt. Rheumatic feverTypically the pain its from joint tojoint, but at the onset one joint may be misleadingly inamed. However, there are no signs of septicaemia. Juvenile rheumatoid arthritisThis may start with pain and swelling of a single joint, but the onset is usually more gradual and systemic symptoms less severe than in septic arthritis. Sickle-cell diseaseThe clinical picture may closelyresemble that of septic arthritis and indeed the bone nearby may actually be infected! So this condition should always be excluded in communities where the disease is common.Gauchers diseaseIn this rare condition acute joint pain and fever can occur without any organism being found (pseudoosteitis). Because of the predisposition to true infection, antibiotics should be given. Gout and pseudo goutIn adults, acute crystal induced synovitis may closely resemble infection. On aspiration the joint uid is often turbid, with a high white cell count; however, microscopic examination by polarized light will show the characteristic crystals.Treatment The rst priority is to aspirate the joint and examine the uid. Treatment is then started without further delay and follows the same lines as for acute osteomyelitis. Once the blood and tissue samples have been obtained, there is no need to wait for detailed results before giving antibiotics. If the aspirate looks purulent, the joint should be drained without waiting for laboratory results (see below).GENERAL SUPPORTIVE CARE Analgesics are given for pain and intravenous uids for dehydration. SPLINTAGE The joint should be rested, and for neonates and infants this may mean light splint age; with hip infection, the joint should be held abducted and 30 degrees exed, on traction to prevent dislocation. ANTIBIOTICS Antibiotic treatment follows the same guidelines as presented for acute haematogenous osteomyelitis (see page 35). The initial choice of antibiotics is based on judgement of the most likely pathogens. Neonates and infants up to the age of 6 months should be protected against staphylococcus and Gram-negative streptococci with one of the penicillinase -resistant penicillins (e.g. ucloxacillin) plus a third generation cephalosporin. Children from 6 months to puberty can be treated similarly. Unless they had been immunized there is a risk of Haemophilus infection. Older teenagers and adults can be started on ucloxacillin and fusidic acid. If the initial examination shows Gram negative organisms a third generation cephalosporin is added. More appropriate drugs can be substituted after full microbiological investigation. Antibiotics should be given intravenously for 47days and then orally for another 3 weeks. DRAINAGE Under anaesthesia the joint is opened through a small incision, drained and washed out with physiological saline. A small catheter is left in place and the wound is closed; suctionirrigation is continued for another 2or 3 days. This is the safest policy and is certainly advisable (1) in very young infants, (2) when the hip is involved and (3) if the aspirated pus is very thick. For the knee, arthroscopic debridement and copious irrigation may be equally effective. Older children with early septic arthritis (symptoms for less than 3days) involving any joint except the hip can often be treated successfully by repeated closed aspiration of the joint; however, if there is no improvement within48 hours, open drainage will be necessary. Haemophilic bleed An acute haemarthrosis closelyresembles septic arthritis. The history is usually conclusive, but aspiration will resolve any doubt. Rheumatic feverTypically the pain its from joint to joint, but at the onset one joint may be misleadingly inamed. However, there are no signs of septicaemia. Juvenile rheumatoid arthritisThis may start with pain and swelling of a single joint, but the onset is usually more gradual and systemic symptoms less severe than in septic arthritis. Sickle-cell diseaseThe clinical picture may closely resemble that of septic arthritis and indeed the bone nearby may actually be infected! So this condition should always be excluded in communities where the disease is common.Gauchers diseaseIn this rare condition acute joint pain and fever can occur without any organism being found (pseudoosteitis). Because of the predisposition to true infection, antibiotics should be given. Gout and pseudogoutIn adults, acute crystal-induced synovitis may closely resemble infection. On aspiration the joint uid is often turbid, with a high white cell count; however, microscopic examination by polarized light will show the characteristic crystals.AFTERCAREOnce the patients general condition is satisfactory and the joint is no longer painful or warm, further damage is unlikely. If articular cartilage has been pre-served, gentle and gradually increasing active movements are encouraged. If articular cartilage has been destroyed the aim is to keep the joint immobile while ankylosis is awaited. Splint age in the optimum position is therefore continuously maintained, usually by plaster, until ankylosis is sound. Complications Infants under 6 months of age have the highest incidence of complications, most of which affect the hip. The most obvious risk factors are a delay in diagnosis and treatment (more than 4 days) and concomitant osteomyelitis of the proximal femur. Subluxation and dislocation of the hip, or instability of the knee should be prevented by appropriate posturing or splint age.Damage to the cartilaginous physis or the epiphysis in the growing child is the most serious complication. Sequelae include retarded growth, partial or complete destruction of the epiphysis, deformity of the joint, epiphyseal osteonecrosis, acetabular dysplasia and pseudo arthrosis of the hip.Articular cartilage erosion (chondro lysis) is seen in older patients and this may result in restricted movement or complete ankylosis of the joint.