Acta Orthop. Belg., 2005, 71, 505-515 REVIEW ARTICLE Osteomyelitis and septic arthritis in children Hugo DE BOECK From the University Hospital VUB, Brussels, Belgium Osteomyelitis is an infection in bone most frequently Osteomyelitis and septic arthritis have a potential occurring in children. The current incidence is 1 in for life-long disability if treated insufficiently. 5000. Septic arthritis is an infection of a synovial joint which may occur in all age groups in children Osteomyelitis but has a specific infantile form affecting the infant from birth to the first year of life. The majority of In children, osteomyelitis is most often acute, infections of bone or joint are caused by spread of bacteriae through the bloodstream or occasionally with the bacteriae usually reaching the bone by entry of organisms through an open wound, by through the bloodstream ; it is commonly referred puncture or by extension of infection from adjacent to as acute haematogenous osteomyelitis (AHO). tissue. The most common causative organism is Rarely an infection may spread to the bone from an Staphylococcus aureus but many other organisms adjacent infected focus or by direct inoculation may be responsible for a bone or joint infection. The through an open wound at the time of an open treatment of both osteomyelitis and septic arthritis is fracture or following surgery. based on antibiotic therapy in combination with sur- gical drainage if pus or infected tissue is present. Acute haematogenous osteomyelitis Early diagnosis followed by adequate treatment gives good outcome. Inappropriate or delayed treatment Acute haematogenous osteomyelitis is predomi- may result in chronic osteomyelitis or irreversible nantly a disease in children. The overall prevalence joint destruction. of AHO is estimated at 1 case per 5000 children (17) Keywords : osteomylitis ; septic arthritis ; children. but according to recent studies the incidence appears to be declining (3, 8, 24). AHO most often is monostotic, affecting nearly twice as many boys as girls (8). The clinical manifestation and the natural INTRODUCTION history of osteomyelitis depend on several factors including age of the patients, site of infection, viru- Osteomyelitis and septic arthritis occur most commonly in children. Osteomyelitis is an inflammation in the bone. ■ Hugo De Boeck, MD, PhD, Professor. Pediatric Orthopaedic Department, University Hospital The term osteomyelitis generally refers to a bacte- VUB, Brussels, Belgium. rial infection of bone. Osteomyelitis may be acute, Correspondence : H. De Boeck, Pediatric Orthopaedic subacute or chronic. Septic arthritis is a joint infec- Department, VUB, Laarbeeklaan 101, B-1090 Brussels, tion usually caused by bacteria. Bacteria can reach Belgium. E-mail : [email protected]. the bone and joint through several routes. © 2005, Acta Orthopædica Belgica. Acta Orthopædica Belgica, Vol. 71 - 5 - 2005 506 H. DE BOECK lence of the infecting organism and patient resis- Table I. — Most common causative organisms by age group tance. The pathogenesis and factors that predispose Newborns (< 2 mo) : Staphylococcus aureus to AHO are poorly understood. The relationship of Streptococcus A and B trauma to osteomyelitis is unclear. Trauma to the Enterobacter bone may cause local oedema and may alter the Children (2 mo - 4 y) : Staphylococcus aureus blood flow, and haematoma seems to provide a Streptococcus A Enterobacter good local environment for bacterial prolifera- Kingellae kingae tion (30). However children are continually subject- Children (5 y - Adult) : Staphylococcus aureus ed to injuries and AHO is relatively uncommon compared to trauma. In some instances there is a history of recent respiratory tract infection, otitis sequestrum. In some locations such as the proximal media or an infected wound but most often AHO femur, the proximal humerus, the proximal radius begins spontaneously in a healthy child. AHO typi- and the lateral part of the distal tibia, the metaphy- cally affects the most rapidly growing ends of long sis lies within the joint capsule and the abscess may bones and is more common in the lower extremity, open into the joint resulting in a concomitant septic the metaphysis of the distal femur and of the prox- arthritis (22). Many different bacteriae can cause imal tibia being the most common sites of infec- osteomyelitis (table I). The organism most com- tion (16, 22). The metaphysis of the proximal monly responsible for AHO is Staphylococcus humerus is less frequently affected. However AHO aureus (1, 3, 8, 11, 16, 17). In neonates, next to Staphy- can develop in any bone of the skeleton. Multifocal lococcus aureus, Streptococcus mainly group B sites of AHO may be present in neonates (17). The and Gram-negative enteric bacteria are frequently anatomical characteristics of the blood supply of found (17). Historically, Haemophilus influenzae the metaphysis of long bones seem to be the major was commonly encountered in children younger factor in the predilection for infection of this area. than 2 years but has now essentially been eliminat- The arterioles of the metaphysis terminate in a ed due to general vaccination against type B sharp loop before emptying into a wide venous Haemophilus influenzae (3, 8, 16, 24, 25). In older sinusoid. The resultant sluggish blood flow creates children, Staphylococcus aureus is by far the most an ideal environment for bacterial proliferation. In common causative organism. In patients with pre- addition there are relatively few phagocytic cells in existing diseases, uncommon organisms may be the metaphyseal vessels so that infection easily encountered. Children with sickle cell disease are develops in this area. The bacteriae provoke an at risk for Salmonella osteomyelitis (21, 26). A punc- inflammatory process. The acute inflammation ture wound through the shoe to the plantar surface increases the vascular permeability, resulting in of the foot may result in Pseudomonas aeruginosa oedema and raised pressure in the venous sinusoids osteomyelitis (16). Methicillin-resistant Staphylo- with thrombosis of the nutrient arteries. If untreat- coccus had emerged as causative organism of ed, the inflammatory process continues. Pressure osteo-articular infections in recent studies (1, 8, 11, within the metaphysis increases as pus collects. With 25). In immunocompromised patients, infections increasing pressure, pus takes the path of lesser caused by fungi must be considered. resistance and perforates the thin cortex of the The clinical response and symptoms of AHO are metaphysis. It then spreads under the periosteum quite variable and depend on the age of the patient, and strips it from the underlying bone, disrupting the site of infection, the resistance of the child and the cortex from its periosteal blood supply. The the virulence of the affecting organism. The onset underlying bone becomes necrotic and then forms of AHO is sudden and is characterised by a well- a sequestrum. The stripped periosteum on the other localised bone tenderness, associated with high hand remains viable and will lay down new bone. fever. The child looks sick and is often unwilling to The newly formed bone is known as an involucrum. move the affected extremity. If the infection is The involucrum may completely encase the located in the lower limb, the patient may limp or Acta Orthopædica Belgica, Vol. 71 - 5 - 2005 OSTEOMYELITIS AND SEPTIC ARTHRITIS IN CHILDREN 507 refuse to walk. Localised signs of inflammation are does not make the definitive diagnosis but it pro- soon present : swelling, redness, warmth, local vides the location of the pathologic process pain. Clinical signs however may be quite variable (fig 1b ; 3c). A bone scan is especially helpful to and the clinical presentation of AHO appears to detect multiple locations such as may occur in the be changing. Many patients now present with less neonate, or when the diagnosis is unclear, with florid illness than the classical presentation (8). In infection in atypical locations such as the case of infection in a deep location such as the pelvis (17). Bone scans will show the site of proximal femur or the pelvis, localised signs such osteomyelitis much sooner than plain radiographs. as redness and swelling are not manifest in the The images of a bone scan are not disturbed by a early phase of the disease. The clinical presentation previous bone aspiration. also differs in neonates. In the neonate there is Computer tomography is not useful as a routine often a lack of signs of systemic illness. Irritability examination in the diagnosis of AHO but may be and poor feeding are then the only findings. valuable in the diagnosis of chronic infection that Pseudoparalysis and pain on attempt at passive may be confused with a tumorous process (17). motion of the affected limb are usually present but Computer tomography is also useful in imaging these signs may be overlooked or misinterpreted. difficult sites such as the pelvis (fig 2d). The paucity of obvious clinical signs in the neonate Magnetic resonance imaging (MRI) should be is responsible for the frequent delay in diagnosis in reserved for diagnostic problems. MRI can provide this age group. additional information about the extent of the Laboratory studies include complete blood cell infection and the localisation of abscess forma- count, erythrocyte sedimentation rate (ESR) and C- tion (8, 25). MRI can also be valuable to detect and reactive protein (CRP). White blood cell count, locate extra osseous soft tissue infections which with a leftward shift, is usually increased. ESR and may mimic bone or joint infection (4, 5). CRP are typically elevated and the values return to The causative organism should be sought by normal after successful treatment. CRP declines blood cultures and by aspiration from the site of and returns to normal values more rapidly (after 7 infection. Cultures should be obtained prior to to 10 days) than ESR (after 3 to 4 weeks). starting antibiotics. Blood cultures are positive in Radiographs show the inflammatory response of 30% to 50% of cases (17). Bone aspiration should the infection.