Musculoskeletal infection can be considered a medical emergency, and as such it is critically important for rheumatologists to make a diagnosis quickly. Accurate diagnosis is essential to successful treatment, which is often shared among multiple specialists. New and emerging pathogens have changed the nature of musculoskeletal infections as well as some of the management strategies.
Definition and Classification
Arthritis related to infection can be regarded as septic, reactive, or postinfectious. Septic arthritis occurs when a viable infectious agent is present or has been present in the synovial space. Although direct bacterial infection of the joint constitutes the most widely recognized form of septic arthritis, direct infection with viruses, spirochetes, or fungi also occurs. Reactive arthritis is a response to an infectious agent that is or has been present in some other part of the body, usually the upper airway, gastrointestinal tract, or genitourinary tract. By definition, viable infectious agents are not recoverable from the synovial space in patients with reactive arthritis, which may be regarded as an immune-related disorder resulting from immunological cross-reactivity between articular structures and infectious antigens. The reactive arthritis group merges pathogenically with diseases such as the spondyloarthritides. Postinfectious arthritis may be considered a special type of reactive arthritis in which immune complexes containing nonviable components of an initiating infectious agent may be present in the inflamed joint. Lyme disease is discussed in Chapter 42 , the reactive arthritides in Chapter 43 , and rheumatic fever and poststreptococcal arthritis in Chapter 44 . In chronic arthritides, which are currently considered aseptic, concerted investigations for infectious agents that use the most powerful techniques of molecular biology may yet demonstrate the causative agent in the joint space. Such techniques have isolated viral antigen or living virus from synovial fluid lymphocytes or membrane and have also demonstrated Borrelia organisms in patients with Lyme disease. Although the study of infectious agents, such as viruses, as possible initiators of some forms of arthritis in children has attracted much attention, it is important to remember that intraarticular and systemic bacterial infections remain the most important curable causes of arthritis in childhood.
Sex Ratio and Age at Onset
Septic arthritis is slightly less common in girls than in boys, who account for 55% to 62% of patients in reported series. Septic arthritis is found most often in the very young and the very old; it may occur in the neonate and is most common in children younger than 2 years old. It diminishes in frequency throughout childhood.
Familial and Geographical Clustering
There does not appear to be a genetic predisposition to septic arthritis. Typical cases of presumed septic arthritis in which no pathogen is identified tend to occur in the summer and fall, but geographical clustering has not been reported. In spirochetal arthritis, such as Lyme disease, there are marked geographic and seasonal outbreaks.
Etiology and Pathogenesis
A wide range of microorganisms can cause septic arthritis in children; Staphylococcus aureus and non-group A and B streptococci are most common overall. However, different organisms are more common at some ages and in certain circumstances ( Table 41-1 ). Haemophilus influenzae type B had been the most common infection identified in children younger than 2 years old, but vaccination of infants for H. influenza has almost eliminated infection with this organism in those areas that routinely and effectively immunize. Streptococcus pneumoniae is a frequent cause of infection in children younger than 2 years old and is common in the older child. After a child reaches 2 years old, S. aureus is the most frequently occurring organism. Group A streptococci and enterococci account for a small proportion of all cases of septic arthritis in childhood and are most prevalent in the age group of 6 to 10 year olds. Salmonella arthritis constitutes approximately 1% of all cases of septic arthritis, and it is commonly associated with sickle cell disease. Infection with Mycobacterium tuberculosis is an unusual cause of septic monoarthritis in childhood. Other rare causes of infectious arthritis in children include Streptobacillus moniliformis (rat-bite fever), Pseudomonas aeruginosa, Bacteroides species, Campylobacter fetus, Serratia species, Corynebacterium pyogenes, Neisseria meningitis, Pasteurella multocida, and Propionibacterium acnes. Kingella kingae is emerging as an important pathogen in children with septic arthritis and may account for a significant portion of culture-negative cases. Most infections with this organism occur in children younger than 5 years old, and 60% occur in children younger than 2. In infants less than 60 days old, the most common causative organisms are S. aureus (40% to 50%) or group B Streptococcus (20% to 25%). Enterobacteriaceae, gonococcus, and Candida species are also rarely pathogens in the neonate. Finally, methicillin-resistant Staphylococcus aureus (MRSA), a particularly virulent organism, although prevalent in southern United States, is increasing worldwide.
|Neonate||Group B Streptococcus|
|Group A Streptococcus|
|Kingella kingae (some areas)|
|Group A Streptococcus|
Septic arthritis usually results from hematogenous spread from a focus of infection elsewhere in the body. Direct extension of an infection from overlying soft tissues (e.g., cellulitis, abscess), bone (e.g., osteomyelitis), or traumatic invasion of the joint accounts for only 15% to 20% of cases. In the hips, shoulders, ankles, and elbows, the joint capsule overlies a portion of the metaphysis, the usual site for osteomyelitis. As a result, if a focus of underlying osteomyelitis breaks through the metaphysis, it can enter the joint and result in septic arthritis.
Joint damage, one of the dreaded sequelae of infection, can result from several mechanisms. Proliferation of bacteria in the synovial membrane results in accumulation of polymorphonuclear (PMN) leukocytes and the inflammatory effects outlined in Chapters 3 and 4 . In septic arthritis, synovial fluid contains high levels of proinflammatory cytokines (tumor necrosis factor [TNF]-α, interleukin [IL]-1β) that mediate cartilage damage by metalloproteinases. The ensuing damage to cartilaginous surfaces of the bone and the supporting structures of the joint may be severe and permanent if treatment is not urgently initiated.
Although trauma or extraarticular infection preceding onset of septic arthritis is common in case histories, knowledge of the etiological significance of these factors is incomplete. In one series, upper respiratory tract infections preceded septic arthritis in approximately 50% of patients, and approximately one third of the patients had received antibiotics within 1 week of onset. A history of a mild, nonpenetrating injury to the affected extremity was elicited in approximately one third of patients. However, all of these studies reflect frequent events in a child’s life, and after onset of serious disease, they are especially prone to recall bias. Intravenous (IV) drug users are at particular risk for septic arthritis of the sacroiliac and sternoclavicular joints, usually caused by Gram-negative organisms. Other recognized risk factors include prosthetic joints, diabetes, alcoholism, recent intraarticular steroids in patients who have a systemic infection, and cutaneous ulcers. Chronic inflammatory arthritis, including juvenile idiopathic arthritis (JIA), may predispose to joint infection.
Septic arthritis is usually accompanied by systemic signs of illness (e.g., fever, vomiting, headache) and may be a component of a more generalized infection that might include meningitis, cellulitis, osteomyelitis, or pharyngitis. Joint pain is usually severe, and the infected joint and periarticular tissues are swollen, hot, and sometimes erythematous, unless muted by partial antibiotic treatment. Passive and active motion of the joint is severely, often completely, restricted (e.g., in the young child this may present as pseudoparalysis). Osteomyelitis frequently accompanies bacterial arthritis, and the presence of bone pain and point tenderness (as opposed to joint pain) should alert the examiner to this possibility. Other sites of hematogenous spread, although less common, are nonetheless important ( Table 41-2 ).
|SITES OF INFECTION||NELSON AND KOONTZ||WELKON ET AL.||SPEISER ET AL.|
|N = 117 (%)||N = 95 (%)||N = 86 (%)|
The joints of the lower extremities are the most common sites of infection, and knees, hips, ankles, and elbows account for 90% of infected joints in children. Septic arthritis affecting the small joints of the hands or feet is rare ( Table 41-3 ). Pyogenic sacroiliac joint disease can occur.
|INFECTED JOINT||FINK AND NELSON||WELKON ET AL.||SPEISER ET AL.||WILSON AND DI PAOLA||OVERALL|
|N = 591 (%)||N = 95 (%)||N = 86 (%)||N = 61 (%)||N = 833 (%)|
|PIP, MCP, MTP||1||—||10||—||2|
Multiple Infected Joints
Although septic arthritis is most often a monoarthritis, two or more joints are infected simultaneously or during the course of the same illness in a few children. In the large clinical experience reported by Fink and Nelson, septic arthritis was monoarticular in 93.4% of patients but affected two joints in 4.4%, three in 1.7%, and four in 0.5%. Multijoint septic arthritis is usually part of generalized septicemia such as with staphylococcus aureus.
Geographical variation exists with up to 24% multisite involvement reported in some studies. Certain immune deficiencies, such as chronic granulomatous disease or acquired immunodeficiency syndrome (AIDS), may predispose to septic arthritis in multiple joints.
A systematic review concluded that in the absence of positive cultures in either the synovial fluid or the blood, the overall clinical judgment of an experienced clinician is superior to laboratory or radiological investigations for the diagnosis of septic arthritis. Recently, a European group used the Delphi technique to achieve consensus on criteria for the definitive diagnosis of septic arthritis. However, the group was unable to reach consensus on criteria for “probable diagnosis” ( eTable 41-4 ). Guidelines for the management of suspected septic arthritis have been published for adults and may be applicable to the older child as well. It is essential that every child with acute unexplained monoarthritis undergo aspiration of the affected joint immediately, because septic arthritis continues to be associated with considerable morbidity and mortality.
|BONE OR JOINT INFECTIONS||DEFINITIVE DIAGNOSIS (EPIDEMIOLOGICAL STUDIES)||PROBABLE DIAGNOSIS (CLINICAL AND THERAPEUTIC STUDIES)|
|Arthritis||Joint fluid aspiration (positive culture and Gram staining, leukocyte count markedly increased and glucose level low) AND blood culture positive||No consensus between two definitions (see ref )|
|Osteomyelitis||Symptoms and signs compatible AND |
Positive bacteriology from a local bone lesion OR
Positive blood culture with indisputable signs of lytic osseous involvement on X-ray or scintigraphy (or MRI) * at some stage of illness
|No consensus between 2 definitions (see ref )|
|Bone or joint infections in general||Signs or symptoms of osteoarticular infections |
AND signs of acute infection on laboratory tests †
AND imaging abnormalities
AND microorganism isolation from at least on one of the following samples: blood, purulent joint fluid, bone biopsy specimen, and abscess fluid
|Presence of at least 1 of these clinical signs |
Fever >38°C + local inflammation (rubor, calor, dolor, tumor)
OR suspicion of osteoarticular infectionOR reduced mobility (limping, rachis rigidity, decreased range of motion in limb or joint)
OR joint swelling
AND at least one of the following signs:
Positive blood culture
OR purulent joint fluid
OR positive culture from a bone or joint aspiration
OR imaging findings (X-ray, ultrasound, or scintigraphy, and/or MRI) consistent with a bone or joint infection ‡
If an anaerobic organism or mycobacterium is suspected, enriched culture medium and special anaerobic culture conditions are necessary. Children in whom septic arthritis is considered should also have cultures of blood and of any potential source of infection (e.g., cellulitis, abscess, and cerebrospinal fluid) performed. Rapid antigen latex agglutination tests for H. influenzae , group B and C streptococci, Neisseria meningitidis , and S. pneumoniae are available in most clinics. The polymerase chain reaction (PCR) has proved useful in detecting evidence of infectious agents in synovial fluid, and real-time PCR may be even more beneficial in the investigation of culture-negative septic arthritis, especially Kingella .
In a group of children with septic arthritis in whom the bacterial agent was identified, Fink and Nelson reported that synovial fluid was culture positive in 307 (79%) of 389 patients. The remaining 21% had positive cultures from sites other than the joint: blood (10%), cerebrospinal fluid (3.8%), blood and cerebrospinal fluid (2.3%), and the vagina (1.3%). Initial inoculation of synovial fluid into blood culture bottles may increase the yield of some organisms, especially Kingella kingae . Although an organism can be identified in one third to two thirds or more of patients by the culturing of all appropriate sites, no causative organisms are ever identified in a significant number of children with pyogenic arthritis. In these patients, the diagnosis of septic arthritis is based on a typical history and the demonstration of frank pus by arthrocentesis. The gross appearance is used to judge the presence (or absence) of pus. As indicated in the next section, although synovial fluid analysis may help, cloudy fluid that precludes reading typed words through a test tube and clinical findings suggest septic arthritis, which may help direct therapy.
Synovial Fluid Analysis
The characteristics of the synovial fluid depend somewhat on the duration and severity of the disease and previous administration of antibiotics. Synovial fluid may appear normal, turbid, or grayish green with bloody streaks. The synovial fluid white blood cell (WBC) count is often markedly elevated, with 90% polymorphonuclear leukocytes (PMN) leukocytes. Speiser and colleagues reported that synovial WBC counts in septic arthritis were less than 50,000/mm 3 (50 × 10 9 /L) in 15% of children; 50,000 to 100,000/mm 3 (50 × 10 9 to 100 × 10 9 /L) in 34%, and more than 100,000/mm 3 (100 × 10 9 /L) in 51%. Fink and Nelson found a relatively low WBC count (less than 25,000/mm 3 or 25 × 10 9 ) in one third of their patients.
The protein content is high (more than 2.5 g/dL) in septic arthritis and the glucose concentration, compared with plasma glucose, is usually low, although it may be normal. A Gram stain identifies the organism in half of untreated patients but in only one fifth of those who have received antibiotics. A Gram stain provides rapid confirmation of bacterial infection and tentative identification of the organism (if the findings are positive), permitting rational antibiotic therapy. Special procedures such as counterimmunoelectrophoresis, latex agglutination, or evaluation by PCR may sometimes identify bacterial antigens in a culture-negative fluid (i.e., blood, urine, or cerebrospinal fluid). These techniques have the advantage of providing antigenic identification much more rapidly than cultures, but they do not provide antibiotic sensitivities. Use of real-time PCR to identify Kingella kingae toxin substantially increases the detection of this organism not identified in routine culture.
At least two blood cultures should always be performed for a child suspected of having septic arthritis. An elevated WBC count with a predominance of PMNs and bands and a markedly elevated erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) level, although of limited help in specific diagnosis, provide a baseline whereby the efficacy of subsequent treatment can be judged. CRP is a better predictor of septic arthritis than the ESR. If the CRP value is less than 1 mg/dL, the likelihood that the patient does not have septic arthritis was 87% in one study. Concentrations of other acute phase reactants are usually increased, but provide no additional useful information.
A number of imaging techniques may be helpful in evaluating a child with septic arthritis Plain radiographs are not diagnostic but might be helpful in excluding other disorders. They may show an underlying osteomyelitis as the etiology of the septic arthritis and may demonstrate only increased soft tissue and capsular swelling. Juxtaarticular osteoporosis reflects inflammatory hyperemia and is evident within several days after onset of infection. Cartilage loss and narrowing of the joint space and subluxation are late findings that develop as the disease progresses. These changes are followed by marginal erosions and eventually by ankylosis ( Fig. 41-1, A, E ). Computed tomography (CT) and especially magnetic resonance imaging (MRI) are additional confirmatory techniques.
The role of CT is generally limited, as other imaging techniques are usually sufficient in children. It may be especially helpful for the evaluation of sacroiliac and sternoclavicular joints. It is also helpful, in combination with ultrasound, to guide aspirations and biopsies.
Detection of joint fluid by ultrasound can help guide fluid aspiration. The sonographic detection of an effusion in the hip of a child treated for osteomyelitis of the femur often indicates the presence of septic arthritis of the joint. Color Doppler may show increased capsular vascularity. In children, ultrasound is the imaging modality of choice for guidance during aspiration or biopsy whenever possible. It may be used in isolation or combination with other imaging modalities.
During the first few days of disease, when plain radiographs show only soft tissue changes, 99mTc-MDP scans reflect hyperemia of the infected area on blood flow studies and increased uptake of the isotope on both sides of the joint. Occasionally, decreased uptake may occur if significant accumulation of intraarticular fluid impedes local blood flow. This technique is useful in the early detection of joint or bone inflammation or infection, but it does not differentiate the two with certainty and cannot differentiate septic arthritis from synovitis from other causes (e.g., JIA). It is helpful in differentiating septic arthritis from osteomyelitis and soft tissue infection, and in the detection of multifocal joint infections. Radionuclide scans with gallium-67 or the patient’s indium-111-labeled granulocytes or monoclonal antibodies may be helpful but are not routinely needed. It is possible that 2-deoxy-2-[ 18 F] fluoro-D-glucose positron emission tomography (FDG-PET)/CT may have an important role in the diagnosis of difficult cases because PET is a relatively fast, whole-body imaging modality and can be used to find infectious foci outside of the bone or joint. It may be particularly helpful for infections of the vertebrae. In general, however, this modality has been replaced by MRI, which provides more detailed information without radiation exposure. PET positivity may help indicate which focus to approach for potential biopsy or aspiration.
Magnetic Resonance Imaging
Delineation of soft tissue structures by MRI is superior to that provided by CT. Changes may be seen as soon as 24 hours following infection. Synovial enhancement is detected in virtually all patients. Signal-intensity alterations in the bone marrow are characteristic, but not diagnostic of, septic arthritis (i.e., low intensity on fat-suppressed, gadolinium-enhanced, T1-weighted, spin-echo images, and high signal intensity on fat-suppressed, T2-weighted, fast spin-echo images) ( Fig. 41-1, B, C ). Articular cartilage and growth cartilage are depicted along with other fibrous structures, muscle, blood vessels, and synovial fluid. An abnormal collection of fluid or debris, often displacing the joint capsule, eroding into other tissues, or, in children, even leading to subluxation, supports the possibility of septic arthritis. Fat-suppressed, gadolinium-enhanced MRI is 100% sensitive and 79% specific for the diagnosis of septic arthritis in adults. MRI may be most helpful in children who do not respond to therapy in the predicted fashion to look for unresolved or other sites of infection in adjacent sites. As technology improves, MRI-guided biopsies or aspirations or other image fusion techniques are becoming useful diagnostic methods when the abnormality is only visible on MRI.
The child with septic arthritis requires hospitalization and consultation with an orthopedic surgeon and usually a specialist in infectious diseases. Nonsteroidal antiinflammatory drugs (NSAIDs) may be used to help minimize the effects of inflammation, to control fever, and to contribute to pain relief. IV dexamethasone has been shown to reduce the duration of symptoms and minimize joint damage in a randomized, double-blind study, but it is rarely, if ever, used. A clinical practice guideline for the management of septic arthritis in children has been proposed. It was demonstrated that this approach was effective in minimizing the use of bone scans, in minimizing the rate of joint drainage, in accelerating the change to oral antibiotic administration, and in shortening the duration of hospital stay. There were no differences in outcomes such as readmission to the hospital, recurrence of infection, or the development of residual joint damage.
In a child with septic arthritis, health care professionals should obtain cultures of blood, joint fluid and any other potential site of infection. IV antibiotics should then be administered as promptly as possible. The main issue that may influence the first dose is the timing of joint aspiration. In general, aspiration is preferred to identify organisms, but if any delay is anticipated, antibiotic treatment should be started as soon as blood cultures are obtained. The choice of antibiotic depends on the presence of predisposing factors; the age of the child; and the organisms suspected because of the Gram stain or rapid antigen detection tests (although it is hazardous to narrow initial treatment based solely on these results because either can be wrong). If the Gram stain and results of rapid antigen detection are negative or not available, an approach based on age (as outlined in Table 41-5 ) is suggested. For uncomplicated osteoarticular infection in infants and children, clindamycin was as effective as cephalosporin. The demonstration of an organism or antigen may support or contradict the generalizations outlined in this table and should influence the physician in selection of the initial antibiotic treatment.
|<3 months||Cefotaxime + nafcillin/oxacillin (if >1 week in NICU, consider using vancomycin)|
|>3 months||If CA-MRSA <10%: nafcillin/oxacillin or cefazolin|
|If CA-MRSA >10%: clindamycin (check for resistance) or vancomycin|
* Every effort should be made to secure cultures and adjust therapy accordingly. Linezolid is an alternative to vancomycin or clindamycin if MRSA is a concern. If Kingella kingae is suspected, use cefazolin.
Although monitoring intravenous antibiotic efficacy with serum bactericidal titer can be performed, it is seldom used unless response to therapy has been unsatisfactory. After satisfactory control—based on a combination of clinical signs such as absence of fever and improved movement of the affected joint plus laboratory parameters such as reduction of the WBC, ESR, and CRP—of the infectious process with IV antibiotic administration is achieved, treatment by the oral route in the hospital or on an outpatient basis may be appropriate. Trials have suggested that the duration of treatment can be shortened to 10 days in total. Home IV antibiotic programs may also be effective in reducing the hospital stay, but they may be associated with complications in up to 30% of children. Such programs should be undertaken only after careful consideration and consultation with an expert in pediatric infectious disease. The criteria for conversion from IV to oral therapy are uncertain. Although many criteria have been suggested, such as resolution of fever, significant decrease in pain, improvement in range of motion, and falling laboratory measures of inflammation, the most useful assessment is when the child starts to move the limb voluntarily with a reducing or absent fever.
If the cultures are negative, IV antibiotics should be continued for a minimum of 21 days. If the child’s clinical state is improving (i.e., temperature returning to normal, pain diminishing, range of motion improving) and the WBC count and ESR/CRP are falling, the initial antibiotics chosen should be maintained. If the patient does not appear to be responding, clinicians need to consider that the drug, dose, route, and compliance are appropriate, and the possibility of the reaccumulation of joint fluid or another site of infection. Because of various patterns of antibiotic susceptibility and resistance, guidelines regarding antibiotic choice and duration of treatment are constantly changing, and the physician is urged to review the most current recommendations. This is especially important with the rise in the incidence of community-acquired Methicillin-resistant Staphylococcus aureus (CA-MRSA), which requires specific antibiotic management. As noted previously, the total duration of therapy is controversial but in uncomplicated septic arthritis in a child who responds rapidly, 10 days is probably sufficient.
Aspiration and Drainage
The usefulness of repeated aspiration and drainage of an infected joint has been hotly debated. There is no dispute that an initial diagnostic arthrocentesis must be performed. Any joint that appears to be under pressure from an effusion can probably benefit from aspiration, if only for pain relief. Studies of the importance of repeated aspirations under other circumstances, however, have failed to show a consistent benefit. Open drainage is no better than closed needle aspiration (except for specific joints such as the hip and shoulder) and is attended by significantly increased morbidity. It is not known whether irrigation of the joint at the time of aspiration provides additional benefit with improved outcome. Occasionally, arthroscopic examination is indicated. Intraarticular administration of antibiotic is unnecessary because therapeutic synovial fluid antibiotic levels are readily achieved, and it may induce chemical synovitis in the infected joint.
Neonatal Septic Arthritis
In addition to S. aureus, group B Streptococcus and Gram-negative bacteria can be the offending organisms in the neonate. Infections with these organisms are rare but potentially extremely serious in this age group. They may have a subtle presentation and can occasionally be bilateral, and they are much more likely to occur in association with osteomyelitis than in older children. Most affected newborns show no fever, toxemia, or leukocytosis. Any infant who has swelling in the region of the thigh or holds the leg flexed, abducted, or externally rotated, or refuses to use the upper limb must be investigated promptly. Problems in early recognition of disease undoubtedly contribute to the often disastrous outcome of this involvement.
Septic Hip Joint
Septic arthritis of the hip is such an important problem that it merits special attention. Because the risks of missing this diagnosis are so high, there must a very low threshold for hip aspiration to establish the diagnosis. The femoral head is intracapsular, and the arterial supply passes through the ligamentum teres into the intracapsular space. Increased intracapsular pressure can therefore interrupt the blood supply to the femoral head, with disastrous consequences to its viability, leading to the subsequent development of avascular necrosis. Metaphyseal osteomyelitis readily leads to septic arthritis of the hip joint in the infant because nutrient blood vessels pass from the metaphysis through the epiphyseal growth plate and terminate in the distal ossification center.
Septic arthritis of the hip joint is most common in infants and very young children; 70% of patients are 4 years old or younger. The typical clinical picture is that of an infant or young child who may have an unexplained fever, is irritable, and refuses to move a leg, bear weight, or walk. Any movement of the hip is extremely painful, and the affected leg is held in a position of partial flexion, abduction, and external rotation at the hip. Occasionally, the child has lower abdominal pain or tenderness, sometimes with paralytic ileus.
The most common differential diagnosis for septic arthritis of the hip in the younger child is transient synovitis or irritable hip syndrome. Transient or toxic synovitis of the hip is an idiopathic disorder often preceded by a nonspecific upper respiratory tract infection. It occurs most commonly in boys (70%) between 3 and 10 years old. Pain in the hip, thigh, or knee may be of sudden or gradual onset and lasts for an average of 6 days. Bilateral involvement occurs in approximately 4% of cases. There is loss of internal rotation of the hip, and the hip may be held in the flexed, abducted position. The ESR and WBC count are usually normal. Radiographs often appear normal or may document widening of the joint space with lateral displacement of the femoral head because of effusion. These findings can be confirmed by CT or ultrasound studies. Radionuclide scanning may demonstrate a transient decrease in uptake of technetium 99m phosphate. Signal intensity is normal with MRI and differentiates toxic synovitis of the hip from a septic process, which is usually the principal differential diagnosis. After a diagnostic ultrasound scan to confirm the presence of fluid, the hip joint should be aspirated to exclude bacterial sepsis if the diagnosis is uncertain. The ability to weight bear and move the hip voluntarily, and the absence of elevated inflammatory markers, all suggest transient synovitis of the hip. The synovial fluid has a normal or minimally increased cell count but may be under high pressure. After aspiration, the pain and range of motion are dramatically improved, at least temporarily. Treatment includes the use of analgesics or NSAIDs, bed rest, and skin traction with the hip in 45° flexion to minimize intracapsular pressure. Long-term sequelae include Legg–Calvé–Perthes disease, which appears in about 1.5% of cases at some point in the future. The only other long-term sequela is the development of coxa magna, which fortunately is of no clinical significance. Recurrences are often accompanied by low-grade fever. Although prediction rules tend not to function well in the general population, possible criteria used to differentiate septic arthritis from irritable hip syndrome include refusal to bear weight; a fever of 38.5°C; ESR greater than 40 mm/hour; and WBC greater than 12 × 10 9 /L. Another study suggested refusal to bear weight and CRP greater than 20 mg/L were highly predictive of septic arthritis.
In very young or premature infants, a number of risk factors predispose to septic arthritis of the hip. In a study of septic arthritis of the hip of 16 infants younger than 4 weeks old, 11 were premature, 7 had an umbilical catheter, and 12 had septicemia. In contrast, of 13 children between the ages of 1 month and 3 years with septic arthritis, none was premature or had an umbilical catheter, and only 5 were septicemic. A high frequency of preceding or accompanying osteomyelitis of the femur or pelvis has been observed. The association of septic arthritis of the hip and femoral venipuncture has been recorded and may account in part for the high frequency of arthritis of this site in the premature neonate.
Management of septic arthritis of the hip requires open drainage to minimize intraarticular pressure. Children are seldom immobilized, instead allowing early passive and active physiotherapy to prevent loss of range of motion. In the unusual circumstance of septic arthritis with subluxation or dislocation, older children require immobilization and neonates require a Pavlik harness for the hip. Prognosis is guarded even with the best treatment, especially in the neonate. The anatomy of the shoulder joint is not unlike that of the hip with respect to vascular supply. Septic arthritis of this joint, although rare, should be treated similarly.
In reported series of septic arthritis in children and adolescents, disease caused by N. gonorrhoeae appears to be uncommon. When it occurs, it is most common in the adolescent, although it occasionally occurs in the neonate in association with disseminated infection. It is more common in girls than in boys and is particularly likely just after menstruation or with pregnancy. Gonococcal arthritis usually develops in patients with primary asymptomatic genitourinary gonorrhea or with a gonococcal infection of the throat or rectum. The patient presents with a systemic illness characterized by fever and chills. A vesiculopustular rash, sparsely distributed on the extremities, commonly yields organisms on culture or Gram stain of the smear. Gonococcal arthritis may have an initial migratory phase and may be accompanied by tenosynovitis. In contrast to most patients with septic arthritis, those with gonococcal arthritis may present with a purulent arthritis of several joints. For a patient with suspected gonococcal arthritis, it is important to culture samples from the genital tract, throat, rectum, and any vesicles in addition to the affected joint. Special culture media with Thayer-Martin agar will help in isolating the organism. The possibility of sexual abuse should be considered and appropriately investigated.
Tuberculous arthritis is seldom encountered in North America or Europe, although its frequency may be increasing because of immunosuppressive therapy, drug-resistant strains of tuberculosis, the human immunodeficiency virus (HIV) epidemic, and international travel. Tuberculous arthritis is by no means rare in other parts of the world. Typically, arthritis arises on a background of pulmonary tuberculosis as indolent, chronic monoarthritis, often of the knee or wrist, which eventually results in extreme destruction of the joint and surrounding bones. It manifests as acute arthritis in rare instances. Occasionally it may present as otherwise typical oligoarticular JIA in the absence of pulmonary disease. If a patient suspected of having oligoarticular JIA fails to respond to intraarticular corticosteroid treatment, the suspicion of tuberculous monoarthritis should be raised, especially if there may be a relevant travel history or contact with people from endemic areas.
Joint infection occurs by hematogenous dissemination of the organism or from adjoining osteomyelitis. For example, hip arthritis can result from spinal infection where organisms track down to the iliopsoas muscle that communicates with the joint. Chronic draining fistulae may develop. Pott disease is a consequence of vertebral osteomyelitis ( Fig. 41-2 ). Tuberculous dactylitis may occur with cystic expansion and destruction of bone (i.e., spina ventosa) ( Fig. 41-3 ). A family or environmental history of pulmonary tuberculosis and a positive purified protein derivative (Mantoux) skin test result suggest the possibility of tuberculous arthritis. Although synovial fluid cultures are positive in approximately 75% of patients, synovial membrane biopsy and culture are preferred and confirm the diagnosis in almost all patients ( Fig. 41-4 ). The synovial WBC count is classically less than 50,000/mm 3 (50 × 10 9 /L), with a high proportion of mononuclear cells. Genus-specific PCR is invaluable in the diagnosis. Rarely, a polyarthritis accompanies tuberculosis (i.e., Poncet’s disease); it probably represents a reactive arthritis because culture of the inflamed joints fails to demonstrate tubercle bacilli.
Another mycobacterial disease that can result in arthritis is leprosy, caused by Mycobacterium leprae. Although the most common clinical manifestations are rash and peripheral neuropathy, arthritis occurs in approximately 75% of cases. Different types of arthritis in leprosy include Charcot joints, septic arthritis, acute polyarthritis, chronic arthritis, and tenosynovitis. Clinical differentiation from JIA may be difficult, especially if the possibility of leprosy is not considered in a nonendemic area; a high degree of clinical suspicion is required to make this diagnosis. Mycobacterium leprae is not always easily identified in synovial biopsies. Serologic testing may be helpful in confirming the diagnosis. Additional cases of leprosy have been reported following the institution of anti-TNF therapy in patients with rheumatoid arthritis.
Arthritis Associated With Brucellosis
Human Brucella infections are reported primarily from Europe, Israel, and South America, with a substantial number of patients having arthritis. Cases that develop in North America are more likely to have been acquired elsewhere. The species most frequently implicated are Brucella melitensis and, less commonly, Brucella canis. Unpasteurized milk is a source of infection.
The systemic illness is often mild in children but is usually characterized by undulant fever, gastrointestinal complaints, lymphadenopathy, and sometimes dermatitis. In 88 children from Israel, the classic triad of fever (91%), arthralgia or arthritis (83%), and hepatosplenomegaly (63%) was characteristic of most patients. In a large series of cases from Peru, almost one third were children, and one third had arthritis. In the neonate to 15-years-old age group, peripheral arthritis of a hip or knee was most common. In patients whose onset was after 15 years of age, sacroiliitis was the most common articular syndrome. Spondylitis and sacroiliac arthritis became predominant after children reached 15 years of age. Gomez-Reino and colleagues found that periarthritis without effusion was most common and that small joints and the spine were not affected. Whether this reflects differences in the infecting organism or in ascertainment is not known. No association with human leukocyte antigen (HLA)-B27 has been demonstrated. Synovial fluid WBC counts are only modestly elevated, with a slight predominance of mononuclear cells. Joint fluid culture is positive for the organism in some patients. Tetracyclines, aminoglycosides, rifampin, and trimethoprim-sulfamethoxazole, often in combination, provide effective treatment of the acute infection, although permanent sequelae may result.
Mycoplasma and Arthritis
Myalgia and arthralgia are common during pulmonary infection with Mycoplasma pneumoniae. Objective oligoarticular, polyarticular, or migratory arthritis has also been described. Sensitive screening tests may uncover Mycoplasma as a cause of arthritis even in the absence of pneumonia.
Bartonella Infection and Arthritis
There have been rare reports of Bartonella henselae infection causing arthritis in children (e.g., cat scratch disease). In two children, the disease mimicked systemic JIA ; a third child had polyarthritis and subcutaneous nodules. Arthropathy occurred in 3% of patients in an Israeli registry. It was characterized by large- and medium-sized monoarthritis, oligoarthritis, or polyarthritis (most commonly symmetric oligoarthritis), which was debilitating. Despite cat scratch disease being a disease of children and adolescents, in this series no patient under 20 years old had joint involvement. The arthropathy usually occurred concurrent with the lymphadenopathy. Erythema nodosum was more common in those with than without arthropathy.
Arthritis in Immunocompromised Patients
Chronic inflammatory arthritis in patients with a primary immunodeficiency is discussed in Chapter 46 . Typical septic arthritis has been reported infrequently in immunodeficient children. Mycoplasma is the most common cause of severe chronic erosive arthritis in patients with congenital immunodeficiency syndromes and has been recovered from joints of patients with AIDS. Ureaplasma urealyticum has been identified in patients with agammaglobulinemia. Candida albicans is occasionally responsible for arthritis in immunosuppressed patients. Patients with HIV have increased incidence of Streptococcus pneumoniae infection that requires broad-spectrum antibiotics.
Course of the Disease and Prognosis
The outcome in septic arthritis is somewhat guarded because permanent damage may occur even with early and appropriate antibiotic treatment. The child usually recovers from the acute illness, but with the passage of time, reduction in range of motion, pain, and eventually degeneration of the surfaces of the affected joint may require surgical intervention. It is estimated that residual dysfunction occurs in 10% to 25% of children, although the changes (e.g., limited joint mobility, joint instability or chronic subluxation) may not be apparent until years later. Recently, a simplified radiographic classification system has been developed to determine prognosis and to guide surgical management of the sequelae of septic arthritis of the hip.
Arthritis Associated With Acne
The association between arthritis and acne has been noted for decades. Most patients are male and have onset of musculoskeletal complications during adolescence. The syndrome includes severe truncal acne followed in several months by fever and arthralgia or arthritis, most often involving hips, knees, and shoulders. Myopathy may also accompany the disorder. It is possible that this syndrome is another example of reactive arthritis. Although arthritis lasts for only a few months in some patients, recurrences over many years have been documented. Treatment with NSAIDs and with antibiotics for control of the acne is indicated. Treatments for acne may also be associated with arthritis, such as minocycline-induced autoimmune phenomena and isotretinoin causing an acute arthritis. Infliximab for the treatment of arthritis has been reported to cause acne. Some cases fall under the category of the pyogenic arthritis pyoderma gangrenosum acne (PAPA) syndrome, reviewed in Chapter 47 . Recurrent attacks of acute episodes of monoarthritis and fever, resembling septic arthritis, may also be seen in patients with familial Mediterranean fever, also reviewed in Chapter 47 .
Whipple disease, first described in 1907, is rare in childhood, although primary infection with the causative organism may cause diarrhea and transitory fever in young children. The disease is caused by the bacterium Tropheryma whipplei, a ubiquitous organism present in the environment, and is characterized by abdominal pain, weight loss, diarrhea, and, in 65% to 90% of patients, arthralgias or arthritis that in most cases precedes other clinical signs by several years. Whipple disease occurs 10 times more frequently in males than in females and is most common in middle age, although it has been identified in young children. Migratory, peripheral joint pain and inflammation lasting hours to months occur over a period of many years, often in association with fatigue, weight loss, and anemia. Joint swelling with increased synovial fluid and restriction of range of motion may occur, although residual deformity does not. The joints most frequently affected are the ankles, knees, elbows, and wrists, and spondylitis has been reported in 20% of cases. Occasionally, arthritis or spondylodiscitis may be present in the absence of gastrointestinal symptoms, and Whipple disease should be considered in patients who are resistant to antirheumatic treatment. A significant percentage of the population, especially those who work with soil or in sewage plants, may be asymptomatic carriers. Periodic acid–Schiff–positive material and bacteria are detectable in macrophages infiltrating the upper small intestine and lymph nodes. Other diagnostic tools include PCR, immunohistochemistry, and electron microscopy. These tests may also be diagnostic on synovial tissue. Because it takes several months to culture the organism, cultures are not recommended as a diagnostic tool. Furthermore, patients with arthritis may not have gastrointestinal (GI) symptoms, and duodenojejunal biopsies will be negative. In such cases PCR is especially important. A genetic predisposition has been suggested based on the ubiquitous nature of the organism, but causative genes have not been identified. Antimicrobial therapy has greatly improved the outcome in this disease. In the absence of neurological involvement, the combination of doxycycline and hydroxychloroquine is the recommended first-line treatment. If there is neurological involvement, sulfadiazine should be added to this regimen. The immune reconstitution syndrome has been reported in several patients following successful treatment.
Although osteomyelitis, like septic arthritis, is most often encountered and treated by specialists in orthopedics and infectious diseases, its frequent association with septic arthritis and the diagnostic problems that it presents require that it be included in this discussion.
Definition and Classification
Bacteria or, rarely, fungi may lead to an intraosseous infection. Historically, osteomyelitis has been classified as acute, subacute, or chronic, based on the duration of symptoms. This classification, based on duration of symptoms, is no longer useful in guiding treatment due to the emergence of MRSA. Classically, acute osteomyelitis is of recent onset and short duration (less than 2 weeks). It is most often hematogenous in origin but may result from trauma such as a compound fracture or puncture wound. It can be metaphyseal, epiphyseal, or diaphyseal in location. Subacute osteomyelitis is of longer duration and is usually caused by less virulent organisms. Chronic osteomyelitis results from ineffective treatment of acute osteomyelitis, or delay in treatment, and is characterized by necrosis and sequestration of bone.
Acute osteomyelitis is somewhat less common than acute septic arthritis. An incidence of 16.7 cases of acute osteomyelitis per year was reported from an institution at which acute septic arthritis occurred at a rate of 28.4 cases per year. However, osteomyelitis may be more common than septic arthritis in developing countries of the world. An incidence rate of 8 per 100,000 children per year has been reported in high-income countries. Although its incidence may be declining in many parts of the world, that is not necessarily the case everywhere. Acute osteomyelitis occurs twice as often in boys as in girls and is more common in younger children. It can occur in the neonate.
Etiology and Pathogenesis
S. aureus (50% to 80%) and the group A streptococci (5% to 10%) are the predominant organisms at all ages. CA-MRSA has emerged as an important pathogen. Up to 15% of children with CA-MRSA who carry the genes encoding Panton–Valentine leukocidin (pvl) have multiple sites of infection. These organisms are also associated with chronic osteomyelitis. Kingella kingae is also an important cause of osteomyelitis, especially in younger children, and specific microbiological techniques may be needed to detect it. Even before specific immunization, H. influenzae seldom caused osteomyelitis (2% to 10%) and should now be even less common. In certain circumstances, specific or unusual organisms (15%) are found. For example, infection of the calcaneus or other bone in the foot associated with a puncture wound through athletic footwear is likely caused by P. aeruginosa. Osteomyelitis caused by S. pneumonia usually occurs in children with associated diseases such as sickle cell anemia, asplenia, or hypogammaglobulinemia, although it has been observed in young infants without underlying disease. Salmonella osteomyelitis is a complication of sickle cell anemia but also occurs in children without sickle cell anemia. In the neonate, group B streptococci, Gram-negative organisms, and Candida in addition to S. aureus are all potential causes of osteomyelitis. B. melitensis uncommonly results in osteomyelitis, but when it does, it has a predilection for the vertebral bodies. Tuberculous osteomyelitis may take various forms and may mimic chronic pyogenic disease, Brodie abscess, tumor, or other types of granuloma. B. henselae (the organism of cat scratch disease) has been identified as the causative agent in a few patients with osteomyelitis.
Fever, bone pain, and tenderness with or without local swelling should suggest the possibility of osteomyelitis. Although a history of prior trauma is elicited in approximately one third of young patients, its significance is uncertain. In the infant, fever may be minimal, and localization of the pain may make it difficult to detect on physical examination. Pseudoparalysis of a limb is often evident. The examiner may find clinical evidence of a preceding systemic infection. The site of the bone infection is usually metaphyseal, and bony tenderness is elicited by pressure near or over the infected area. The presence of a joint effusion adjacent to the site of bone infection may reflect septic arthritis or a sterile noninflammatory “sympathetic” effusion. With delay in treatment or the presence of virulent organisms such as MRSA, the local signs, usually due to abscess formation, resemble cellulitis.
Osteomyelitis in children has a predilection for the metaphysis of rapidly growing bone. Many explanations have been suggested for this tendency. The anatomical differences in vasculature in this area in children and its easily compromised blood supply may in part explain the clinical observation (see Chapter 2 ). In one anatomical model, bacteremia and, in some cases, preceding microtrauma were sufficient to initiate disease. The bones of the lower extremity are affected in 66% of patients; those of the upper extremity account for approximately 25%, but those of the skull, face, spine, and pelvis are the sites of infection in fewer than 10% ( Table 41-6 ). Fewer than 10% of children have two or more simultaneously infected bones; in some cases, five or more bones are involved as part of a severe septicemic illness, usually caused by staphylococci. This type of involvement must be distinguished from chronic recurrent multifocal osteomyelitis (see Chapter 48 ).
|BONE||OSTEOMYELITIS * (%)|
|Metatarsus, metacarpus, phalanx||4|
* Data from C.W. Fink, J.D. Nelson, Septic arthritis and osteomyelitis in children, Clin. Rheum. Dis. 12 (1986) 423, and from W.G. Cole, R.E. Dalziel, S. Leitl, Treatment of acute osteomyelitis in childhood, J. Bone Joint Surg. Br. 64 (1982) 218.
Acute osteomyelitis can be associated with the development of deep-vein thromboses (DVT). In a series of 35 patients from Dallas who had osteomyelitis involving the proximal humerus, femur, proximal tibia or fibula, pelvis, or vertebrae, 10 had evidence of DVT based on imaging studies, although it was only symptomatic in one patient. In two patients, the DVT was related to a central catheter placed for long-term antibiotic therapy, whereas in the remaining eight, the DVT occurred in veins adjacent to the site of infection. The authors attributed the DVTs to the inflammatory response leading to localized endothelial damage and activation of the coagulation cascade. Compounding factors include the local edema, venous compression and immobility in patients with lower extremity involvement. Organisms with the pvl gene were more likely to be associated with DVTs. Features that suggest methicillin-resistant versus methicillin-sensitive Staphylococcus aureus osteomyelitis include a temperature of higher than 38°C; hematrocrit at less than 34%; WBC greater than 12,000; and CRP greater than 13mg/L.
Compared with acute osteomyelitis, patients with subacute osteomyelitis, defined as disease duration between 2 weeks to 3 months, experience less pain, often have no fever, and have frequently received a course of antibiotics. Laboratory changes are less common, but radiographs are usually abnormal and may be confused with Ewing sarcoma or osteoid osteoma. Brodie abscess, a unique form of subacute osteomyelitis, is usually of staphylococcal origin and may develop after a penetrating injury or more likely by hematogenous spread of an infection to the metaphysis. It is characterized clinically by tenderness with pain that may awaken the child at night. Radiographs demonstrate only soft tissue swelling early, but eventually metaphyseal osteolytic lesions are evident. They are most common in the proximal or distal ends of the tibia ( Fig. 41-5 ). Culture of the abscess may be negative. Treatment includes IV antibiotics, an NSAID, and immobilization.
Chronic osteomyelitis develops when acute osteomyelitis has been inadequately treated, or it develops in states of impaired host or antibiotic resistance. Reduced blood flow leads to the formation of a sequestrum, which may be surrounded by a sleeve of periosteal new bone (involucrum). Complications of chronic osteomyelitis include growth plate arrest or stimulation, avascular necrosis, pathological fracture, septicemia, and if it becomes chronic, amyloidosis.
Neonatal osteomyelitis merits special consideration. Until a child reaches the age of approximately 18 months, metaphyseal blood vessels can cross over the open physis into the epiphysis, permitting infection to move across the growth plate. The thin cortical bone of newborns allows infection to spread rapidly into the subperiosteal region, and the relative immune deficient state of the newborn allows for rapid spread. The lack of a systemic inflammatory response often leads to a delay in diagnosis, and involvement of more than one site is common. Although S. aureus remains the most common organism responsible for neonatal osteomyelitis, especially in newborns with central lines, group B streptococci, Gram-negative bacteria, and Candida albicans may also be responsible.
As in septic arthritis, it is essential that every reasonable attempt be made to identify the organism and determine its antibiotic susceptibility. Recently, a European group of experts arrived at a consensus definition of osteomyelitis. A high index of suspicion for this diagnosis must be maintained in any child with unexplained pain, fever, limp, or lack of use of an extremity. Aspiration of subperiosteal pus, if present, can be used for diagnosis and, together with cultures of the blood, synovial fluid, or an infected wound, should yield an organism in approximately 70% to 80% of cases. Blood cultures alone are positive in 30% to 50% of infants and children with osteomyelitis. A bone biopsy may be desirable or necessary if other sites of culture prove negative. The elevated WBC count, CRP, and ESR are nonspecific and provide little help with diagnosis; they are useful in assessing effectiveness of therapy.
Radiographic evaluation may delineate soft tissue swelling early, but osteopenia is not evident until days 10 to 14, and diagnostic findings may not be clear until days 10 to 21 ( Fig. 41-6 ). Radionuclide scanning (i.e., technetium 99m polyphosphonate or diphosphonate) provides a sensitive if nonspecific method for the early detection of increased blood flow and uptake in the infected bone (see Fig. 41-6C ). While a bone scan may be helpful in localizing osteomyelitis in the neonate or infection of the axial skeleton and in searching for subclinical areas of infection in multifocal osteomyelitis, it is seldom used. A positive result is not necessarily diagnostic of osteomyelitis, but a negative scan is unlikely for a child with bacterial osteomyelitis, except in the very early stages of the illness.
MRI is superior to other modalities in identifying changes in the marrow (see Fig. 41-6, D ). T1- or T2-weighted MR images and fat-suppression enhancement can confirm a focal area of increased inflammatory exudate (i.e., protons or water). A major advantage of MRI in early disease over plain radiographs, ultrasonography, or CT is the delineation of soft tissue or subperiosteal pus. Gadolinium does not add to diagnostic accuracy except in the young child in whom it may detect involvement of nonossified growth cartilage.
As noted above, historically, acute osteomyelitis would respond to antibiotic therapy. However, with the emergence of MRSA the duration of symptoms may not be an accurate guide to disease severity. A more useful designation may be to consider osteomyelitis as complicated or uncomplicated . Complicated osteomyelitis presents with local findings of cellulitis, radiographic findings, or systemic toxicity with high fever, high WBC, and elevated ESR/CRP. While antibiotic care is needed in all cases, complicated osteomyelitis requires MR imaging and may need surgical therapy.
Following a practice guideline in a nonrandomized retrospective study reduced the length of hospital stays and readmission rates. While somewhat dependent on local prevalence, in the absence of specific indications to the contrary, the initial antibiotic choices in many areas for the treatment of acute osteomyelitis should be effective against MRSA (see Table 41-5 ). Screening of S. aureus for inducible clindamycin resistance with the D-test helps determine whether the patient should be treated with clindamycin or vancomycin. Linezolid may become an important oral agent in the initial treatment and in the treatment of clindamycin-resistant MRSA, although studies to date are limited. IV antibiotics for 4 to 6 weeks have been traditionally recommended with subsequent oral coverage if appropriate. Because of the complications that may occur from central venous catheters required to maintain IV access for uncomplicated osteomyelitis, recent recommendations have included a shortened total course of 3 weeks of antibiotic treatment. The decision to transition from IV to oral antibiotic is guided by the clinical response (e.g., the use of the limb and decreasing fever).
Surgical treatment, which may be needed in complicated osteomyelitis, includes drainage of subperiosteal and soft tissue abscesses and debridement of associated lesions. Surgery is also often needed for subacute and chronic osteomyelitis. Although early weight bearing is permitted with uncomplicated osteomyelitis, it must be avoided in complicated osteomyelitis to prevent risk of fracture.
Course of the Disease and Prognosis
The most dreaded complications of acute osteomyelitis are chronic osteomyelitis and impaired bone growth. Chronic osteomyelitis or alternative sites of infection should be suspected in a child whose systemic symptoms have responded slowly or incompletely to antibiotics or in whom there is a late recurrence of pain at the affected site.
Differential Diagnosis and Related Disorders
Chronic recurrent multifocal osteomyelitis and synovitis, acne, pustulosis, hyperostosis, and osteomyelitis syndrome are discussed extensively in Chapter 48 .
There is considerable dispute about whether diskitis is an infectious process. Infection of an intervertebral disk space from osteomyelitis of an adjoining vertebral body is rare. However, acute diskitis unassociated with vertebral osteomyelitis is a self-limited inflammation of an intervertebral disk that may be caused by pathogens of low virulence, although bacteria or viruses are seldom recovered by aspiration. S. aureus and Enterobacteriaceae or Kingella organisms are responsible in some patients. Diskitis occurs throughout childhood, but one half of the cases manifest before the patient reaches 4 years of age (peak age, 1 to 3 years old). The sex ratio is approximately equal, although one review observed that diskitis occurred more frequently in girls.
Clinical signs may be subtle. Diskitis is characterized by vague back pain and stiffness, often resulting in a characteristic tripod position during sitting or other unusual posturing. The child, who usually has a low-grade fever, often refuses to walk, stand, or bend over, and may complain of abdominal pain. Palpation of the spine may produce localized tenderness, usually in the lower lumbar region. The ESR is usually moderately elevated.
Plain radiographs of the affected area often appear normal until late in the disease ( Fig. 41-7 ). A technetium 99m bone scan or MRI is valuable diagnostically. The L4-L5 interspace is most often affected (44%), followed by L3-L4 (37%), L2-L3 (7%), and L5-S1 (6%). The cervical spine may also be involved. In one study, disk space narrowing occurred in 82% of children, and a bone scan was positive in 72%. MRI may be valuable in differentiating infection from other conditions, including idiopathic disk calcification ( Fig. 41-8 ). Aspiration of the disk space or disk biopsy should not be routinely necessary. Immobilization provides symptomatic relief. With signs of systemic infection, IV antibiotics should be instituted until results of blood cultures are available.