Bacterial infections of the neonatal skeletal system are potentially disabling because of damage to the articular cartilage and epiphysis. Prompt diagnosis and treatment are imperative to prevent sequelae.2,16 Unfortunately, neonates with skeletal infections do not usually have the classic symptoms or laboratory findings of sepsis because of their immature immune systems. Diagnosis requires a high index of suspicion and appropriate evaluation. When infections involve the bone, the disease process is called osteomyelitis. When the synovium (the membrane lining of the joint) is the primary site of infection, the process is called septic arthritis (see Part 10).8 In childhood, there is no connection between the epiphyseal and metaphyseal blood supply. The physis creates a barrier that is seldom penetrated by the spread of infection from the metaphysis to the epiphysis or from the epiphysis to the metaphysis. However, during the first 12 to 18 months of life, this barrier to the spread of infection does not exist because there are vessels passing through the physis that connect the epiphyseal and metaphyseal circulations.2,3,15 These vessels allow infections to cross the physis, which may account for the increased incidence of physeal damage seen in neonatal osteomyelitis when compared with childhood osteomyelitis.2,8,16 Peters and associates16 observed the late onset of growth disturbance after neonatal osteomyelitis and recommended that the affected neonates be followed to skeletal maturity to monitor for growth disturbances. When bacteria lodge in the metaphyseal vessels and begin to proliferate, inflammation followed by abscess formation occurs. The pressure from the purulent material causes extrusion of the pus through the haversian canals to the cortex and subsequently into the subperiosteal space. The continued subperiosteal accumulation of purulent material strips the periosteum from the bone. Because the periosteum supplies blood to the cortex, this stripping process interrupts cortical blood flow. As a result, large areas of cortical bone may become devascularized. This dead bone, or sequestrum, can serve as a site for chronic infection, which is isolated from limited neonatal defense mechanisms and antibiotics.15 The elevated periosteum produces new bone in an attempt to repair the injured bone. This process in turn produces the involucrum, which surrounds the sequestrum. Draining cutaneous sinuses may arise when pus ruptures through the periosteum, adjacent soft tissues, and skin. Infection may occasionally spread into an adjacent joint space, causing secondary septic arthritis. The destruction of the epiphysis may occur through the direct spread of infection into it. This process can result in subsequent shortening, angular deformity, or both, of the involved extremity.16 In neonates, complete physeal closure can occur, resulting in shortening.2 Damage to the articular surface of the joint may result in the loss of motion and ultimately degenerative osteoarthritis. The etiologic organisms responsible for neonatal osteomyelitis are variable. Staphylococcus aureus has traditionally been the most common causative organism.2 Methicillin-resistant S. aureus (MRSA) has been reported in neonates, which is especially destructive.11 Streptococci and enteric aerobic bacilli account for much of the remaining responsible organisms. Candida albicans can also cause osteomyelitis in those neonates at high risk for infection. The clinical manifestations of osteomyelitis in children vary with age. In previously healthy neonates, it usually occurs during the first 2 weeks of life. Limitation of spontaneous movement with pseudoparalysis of the involved extremity is the most common sign. Localized tenderness, erythema, increased warmth, and swelling may occur. Associated septic arthritis with accompanying joint effusion and increased warmth occurs in many cases. Term neonates usually appear less ill than would be expected because of the persistence of maternal antibodies. They have less fever, leukocytosis, and elevation of the erythrocyte sedimentation rate2 than older children with similar infections. Less commonly, neonatal osteomyelitis presents as septicemia. The presentation and course of osteomyelitis are strongly correlated with the health of the infant before presentation. Infants with multiple sites of infection are usually ill before its onset and have an increased incidence of placement of umbilical catheters or other lines. They are also more ill than those neonates presenting with only one site of infection.2 Some neonates are at increased risk for osteomyelitis; they also have a more severe course of the disease. Bergdahl and colleagues2 identified the following risk factors in a study of 40 neonates with osteomyelitis: a birth weight of less than 2500 g or gestational age of less than 37 weeks, emergency cesarean delivery, a congenital malformation requiring neonatal surgery, respiratory distress syndrome, hyperbilirubinemia, large vessel (usually umbilical) catheterization, perinatal asphyxia, scalp laceration after vacuum extraction, and renal vein thrombosis. Twenty-one neonates were found to have risk factors, but 19 did not. Of the 21, most had multiple sites of infection; 13 of the 21 (62%) neonates with risk factors had serious skeletal sequelae. In the remaining 19 neonates, multiple sites of infection were uncommon, and serious skeletal sequelae occurred in less than 20%. The early diagnosis of osteomyelitis is based on obtaining purulent material, blood, or both for cultures and antibiotic sensitivities. Early in the course of the disease, radiographs and bone scans may be normal.1,3,5 Bone aspiration is usually positive. The cultures of subperiosteal metaphyseal pus yield a pathogen in about 70% of cases. The point of maximal swelling, bone tenderness, and fluctuation on physical examination is the most appropriate location for needle aspiration. The skin overlying the affected region should be prepared with an antiseptic solution and draped with sterile towels. After infiltration of the area with local anesthetic, an 18-gauge spinal needle, with the stylet in place, is passed through the skin to the bone. The subperiosteal space is aspirated first. If the tap is dry, the needle with the stylet should be gently twisted through the bone cortex into the metaphysis, which is then aspirated. The aspirated fluid or blood should be immediately Gram stained and cultured. The organism may also be recovered from other sources. Blood cultures are positive in 60% of the children with osteomyelitis. When osteomyelitis complicates meningitis, the organism may be recovered from cultures of the cerebrospinal fluid. See Chapter 40. A diagnosis cannot be easily made by bone aspiration during the inflammatory phase before abscess formation. At this point, imaging can be helpful. Plain radiographs of the suspected bone are often a valuable procedure. Within a few days of the onset of infection, deep edema, joint effusion, and sometimes bone destruction can be detected.2 The edema is visible sooner in neonates than in children because the neonate has very porous bones and a loosely attached periosteum (Figure 106-1), which permits the earlier collection of subperiosteal abscesses in neonates than in children. This fact also accounts for the relatively favorable results of diagnostic aspiration in neonates.
Bone and Joint Infections in Neonates
Osteomyelitis
Pathology and Etiology
Diagnosis
Imaging
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Bone and Joint Infections in Neonates
