AAOS Comprehensive Orthopaedic Review

Section 3 - Pediatrics

Chapter 28. Osteoarticular Infection

I. Osteomyelitis

A. Overview

 

1. Usually occurring in the first decade of life, osteomyelitis affects 1 in 5,000 children younger than 13 years.

 

2. It is 2.5 times more common in boys than girls.

 

3. Advances in antimicrobial therapy have decreased the mortality from 50% to less than 1%.

 

4. The emergence of more resistant, virulent strains of bacteria has added complexity to the management of affected children.

 

B. Acute hematogenous osteomyelitis (AHO)

 

1. Overview

 

a. AHO is the most common type of osteomyelitis.

 

b. Risk factors for developing AHO

 

i. Diabetes mellitus

 

ii. Chronic renal disease

 

iii. Hemoglobinopathies

 

iv. Rheumatoid arthritis

 

v. Concurrent varicella infection

 

vi. Immune compromise

 

c. Healthy children are often affected.

 

2. Pathophysiology

 

a.

Pathoanatomy

i. Acute osteomyelitis

 

a. Most cases of acute osteomyelitis are hematogenous.

 

b. Bacteremia may result from a violation of the skin, a concurrent infection, or something as simple as brushing the teeth.

 

c. Slow blood flow in the capillaries of the metaphysis allows bacteria to exit the vessel walls.

 

d. If a sufficient number of bacteria lodge in the bone to overwhelm the local defenses, an infection occurs.

 

e. Osteoblast necrosis, activation of osteoclasts, release of inflammatory mediators, recruitment of inflammatory cells, and blood vessel thrombosis cause a purulent exudate.

 

f. A subperiosteal abscess forms when the exudate penetrates the porous metaphyseal cortex.

 

g. In bones with an intra-articular metaphysis, the exiting exudate can enter the joint and cause an associated septic arthritis.

 

ii. Chronic osteomyelitis

 

a. Periosteal elevation may deprive the underlying cortical bone of its blood supply, creating a necrotic piece of bone (sequestrum).

 

b. The periosteum may form an outer layer of new bone (involucrum).

b.

Mechanism

i. Local trauma has been associated with the development of AHO because the bone becomes more susceptible to bacterial seeding.

 

ii. The combination of trauma and bacteremia seems requisite. Either one in isolation does not appear to cause AHO.

c.

Bacteriology (

Table 1)

i. In all age groups, most cases of AHO are caused by Staphylococcus aureus.

 

ii. There has been a tremendous increase in infections caused by community-acquired, methicillin-resistant S aureus (CA-MRSA).

 

a. Some strains of CA-MRSA harbor genes encoding for Panton-Valentine leukocidin (PVL).

 

b. PVL-positive strains of CA-MRSA are associated with complex infections with more multifocal infections, prolonged fever, myositis, pyomyositis, intraosseous

 

[Table 1. Causative Organisms and Initial Empiric Therapy for Osteomyelitis and Septic Arthritis]

 

or subperiosteal abscesses, chronic osteomyelitis, and deep venous thrombosis.

 

3. Evaluation—The presentation of children with AHO can vary from an intermittent limp and low-grade fever to septic shock.

 

a.

History

i. The history should cover fever, pain, limp, refusal to bear weight, and recent local trauma or infections.

 

ii. Immunization history must be obtained, particularly with regard to Haemophilus influenza vaccination.

 

iii. Use of antibiotics may mask symptoms.

b.

Examination

i. The child should be examined for

 

a. General appearance

 

b. The ability to bear weight or walk

 

c. Point tenderness (including the pelvis, spine, and lower extremities)

 

d. Range of motion (ROM) of adjacent joints (including spine ROM)

 

e. Increased warmth, edema, and erythema

 

ii. Temperature and vital signs should be measured to rule out hemodynamic instability.

c.

Laboratory findings

i. Initial blood work should include C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), blood cultures, and white blood cell (WBC) count with differential.

 

ii. The CRP is elevated in 98% percent of patients with AHO and becomes abnormal within 6 hours.

 

iii. The ESR becomes elevated in 90% of patients with osteomyelitis, and peaks in 3 to 5 days.

 

iv. Blood cultures may yield an organism 30% of the time.

 

v. The WBC is elevated in only 25% of patients.

d.

Diagnostic imaging

i. Plain radiographs do not show bone changes for 7 days but can demonstrate deep soft-tissue swelling and loss of tissue planes.

 

ii. Technetium Tc 99m bone scan can help localize the focus and will demonstrate a multifocal infection.

 

a. The overall accuracy is 92%.

 

b. A "cold" bone scan is associated with more aggressive infections, possibly requiring surgical treatment.

 

iii. MRI

 

a. Has sensitivity of 88% to 100%.

 

b. MRI detects marrow and soft-tissue edema seen early in infection as well as abscesses requiring surgical drainage.

 

c. MRI assists with preoperative or postoperative planning when there is a poor clinical response to antibiotic therapy or after surgical drainage.

 

iv. CT demonstrates abscess formation and bony changes but is most helpful later in the disease course.

c.

Differential diagnosis—The differential diagnosis for AHO includes cellulitis, septic arthritis, toxic synovitis, fracture, thrombophlebitis, rheumatic fever, bone infarction, Gaucher disease, and malignancy (including leukemia).

 

4. Treatment

 

a. Aspiration—Aspiration of the suspected area is the first step in management.

 

i. Aspiration is performed before commencing antibiotics if the clinical condition of the patient allows.

 

ii. Diagnostic aspiration helps guide the medical management when the organism is identified (50% of cases).

 

iii. Susceptibilities and resistant strains of CAMRSA vary by community, adding to the importance of cultures.

 

iv. A large-bore needle is used to aspirate both the subperiosteal space and the intraosseous space.

 

v. After aspiration, antibiotics may be started according to the guidelines in Table 1.

 

b. Nonsurgical

 

i. If no purulent material is aspirated, the child can be admitted for intravenous antibiotics. Because of its frequency, CA-MRSA should be covered in most (if not all) cases.

 

ii. Surgery is not indicated if the patient demonstrates clinical improvement within 48 hours.

 

iii. Duration of intravenous antibiotics is usually 4 to 6 weeks.

 

c. Surgical

 

i. Indications for surgical drainage

 

(a) Aspiration of pus

 

(b) Abscess formation on imaging studies

 

(c) Failure to respond adequately to nonsurgical treatment

 

ii. Contraindications—Hemodynamic instability is a contraindication to emergent surgery, and the child should be stabilized first.

 

iii. Procedures

 

(a) Surgical drainage requires evacuation of all collections of pus, debridement of devitalized tissue, and drilling the cortex to drain intraosseous collections.

 

(b) Samples should be sent for culture and histology to rule out neoplasm.

 

(c) The wound can be closed over drains if deemed adequately debrided, or packed and re-debrided after 2 to 3 days before closure over drains.

 

(d) With chronic osteomyelitis, a more aggressive debridement may be necessary, at times including excision of the sequestrum.

 

5. Complications of AHO

 

a. Meningitis

 

b. Chronic osteomyelitis

 

c. Septic arthritis

 

d. Growth disturbance

 

e. Pathologic fracture

 

f. Limb-length discrepancy

 

g. Gait abnormality

 

h. Deep venous thrombosis

 

C. Subacute osteomyelitis

 

1. Overview

 

a. Subacute osteomyelitis is an uncommon infection characterized by bone pain and radiographic changes without systemic signs.

 

b. Delayed diagnosis is common.

 

c. Usually affects lower extremity long bones, but it can occur in other sites.

 

2. Pathoanatomy

 

a. The genesis of subacute osteomyelitis is the same as acute osteomyelitis.

 

b. The difference in presentation results from increased host resistance, less virulent organisms, prior antibiotic exposure, or a combination of these factors.

 

c. Bacteriology—S aureus causes most cases.

 

[

Figure 1. Radiographic classification of subacute osteomyelitis. Types IA and IB indicate lucency; type II, metaphyseal with loss of cortical bone; type III, diaphyseal; type IV, onion skinning; type V, epiphyseal; and type VI, spine.]

3. Evaluation

 

a. History

 

i. The history is notable for the absence of fever, malaise, or anorexia.

 

ii. The only symptom may be an intermittent limp or pain.

 

b. Physical examination—Point tenderness over the involved bone is often the only clinical finding.

 

c. Laboratory findings

 

i. Blood tests are usually not helpful.

 

ii. The WBC is usually normal or slightly elevated, the ESR slightly elevated, the CRP normal, and blood cultures negative.

 

d. Diagnostic imaging

 

i. Plain radiographs are positive for changes that range from a well-circumscribed radiolucency in the metaphysis or epiphysis to periosteal new bone formation suggestive of an aggressive malignancy.

 

ii. Bone scan is usually positive.

 

iii. CT and MRI help characterize the lesion, but MRI provides more information.

 

4. Classification

 

a. The classification is based on the appearance of the lesion on plain radiographs (Figure 1).

 

b. In all cases, the plain radiograph differential diagnosis includes neoplasm.

 

5. Treatment

 

a. Nonsurgical

 

i. Lesions without malignant features may respond to antibiotic therapy covering S aureus.

 

ii. Surgery is most commonly needed in cases of subacute osteomyelitis.

 

b. Surgical

 

i. Indications

 

(a) Surgical treatment is indicated in all patients with aggressive features on radiographs (types II, III, and IV).

 

(b) A biopsy is required to rule out a malignancy if such radiographic features are present.

 

ii. Procedures

 

(a) A biopsy and culture is performed, using an approach that does not contaminate more than one muscle compartment (in case a malignancy, rather than infection, is present).

 

(b) Once osteomyelitis is confirmed, the lesion can be treated with curettage and antibiotics.

 

6. Complications

 

a. Growth disturbance (unusual)

 

b. Chronic osteomyelitis



II. Septic Arthritis

A. Overview

 

1. Septic arthritis is a surgical emergency.

 

a. Delayed treatment can cause permanent joint damage, deformity, and long-term disability.

 

b. Poor outcomes follow delayed diagnosis.

 

2. The incidence of septic arthritis peaks in the first few years of life.

 

a. 50% of cases of septic arthritis occur in children younger than 2 years.

 

b. Large joints like the hip (35%) and knee (35%) are most commonly involved.

 

B. Pathoanatomy

 

1. Pathophysiology

 

a. Most cases of septic arthritis result from:

 

i. Bacteremia seeding the joint

 

ii. Direct inoculation of the joint from trauma or surgery

 

iii. Contiguous spread from adjacent osteomyelitis

 

b. Release of proteolytic enzymes from inflammatory cells, synovial cells, cartilage, and bacteria may cause damage to the articular cartilage within 8 hours.

 

c. Increased joint pressure in the hip may cause osteonecrosis of the femoral head if not promptly relieved.

 

2. Bacteriology (Table 1)

 

a. S aureus causes >50% of cases.

 

b. The incidence of H influenza septic arthritis has decreased markedly since the advent of the H influenza vaccine.

 

C. Evaluation

 

1. History

 

a. The history of septic arthritis is similar to osteomyelitis.

 

b. A history of rash or swollen lymph nodes is important for their association with other conditions in the differential diagnosis.

 

c. The vaccination history must be obtained.

 

2. Physical examination

 

a. Patients have fever and often appear toxic.

 

b. There is disuse of the extremity and/or refusal to bear weight.

 

c. Septic joints have an associated effusion, tenderness, and warmth; any motion causes severe pain.

 

d. The extremity rests in the position that maximizes the volume of the joint; for the hip, this results in hip flexion, abduction, and external rotation (FABER).

 

3. Laboratory findings

 

a. The WBC is elevated (leukocytosis) in 30% to 60% of patients, and 60% of those will have a left shift.

 

b. The ESR is often elevated but may be normal early in the course.

 

c. An elevated CRP is the most helpful.

 

d. Blood cultures should be drawn because these are often positive, even when local cultures are negative.

 

4. Diagnostic imaging

 

a. Plain radiographs may show joint space widening and are needed to identify any possible bone involvement.

 

b. Ultrasound confirms the presence of a hip effusion and can be used to guide joint aspiration; ultrasound cannot differentiate between septic and sterile effusions.

 

c. MRI detects a joint effusion and can assess for adjacent osseous involvement, but it can be difficult to obtain expeditiously.

 

5. Aspiration

 

a. Joint aspiration is necessary for diagnosis.

 

b. Fluid samples should be analyzed for cell count with differential (

Table 2), Gram stain, and culture.

 

6. Differential diagnosis

 

a.

The differential diagnosis includes osteomyelitis, toxic synovitis, viral arthritis, inflammatory bowel disease-associated arthritis, post-gastroenteritis arthritis, tuberculosis (TB), Lyme disease, poststreptococcal arthritis, juvenile arthritis, Reiter syndrome, reactive arthritis, villonodular synovitis, leukemia, sickle cell disease, hemophilia, serum sickness, and Henoch-Schonlein purpura.

i. Children with septic arthritis appear sicker and are in more distress than those with toxic synovitis.

 

ii. Children with synovitis appear comfortable and may be playful when the hip remains still.

 

iii. Juvenile rheumatoid arthritis (JRA) rarely presents in the hip.

 

[Table 2. Synovial Fluid Analysis]

b.

For the hip, slipped capital femoral epiphysis, Legg-Calve-Perthes disease, fracture, and psoas abscess belong in the differential.

 

7. Diagnosis—Accurate diagnosis requires synthesis of the clinical findings, laboratory studies, imaging, and judgment.

 

a. If all four of the following are present, the probability of septic arthritis ranges from 59% to 99.6% in various series:

 

i. Fever >38.5°C

 

ii. Inability to bear weight

 

iii. ESR >40 mm/h

 

iv. WBC >12,000/μL

 

b. A CRP >2.0 mg/dL is an independent risk factor for septic arthritis.

 

c. The order of importance of predictors is: fever >38.5°C, elevated CRP, elevated ESR, refusal to bear weight, and an elevated WBC.

 

D. Treatment

 

1. Initial

 

a. Treatment starts with joint aspiration, preferably before starting antibiotics empirically (Table 1).

 

b. Intravenous antibiotics are started after samples are sent for culture, and are usually administered for 3 weeks. The child's immunization status should be checked to determine whether H influenzaeneeds to be covered by the empiric antibiotics.

 

2. Nonsurgical—There is rarely a role for nonsurgical treatment, although some authors advocate intravenous antibiotics and serial aspirations for accessible joints.

 

3. Surgical

 

a. Indications—Surgical drainage and irrigation is the standard of care for almost all septic joints, to clear the joint of damaging enzymes. With possible septic arthritis of the hip, it is better to err on the side of drainage. The morbidity from surgical drainage is much less than that from a neglected septic hip.

 

b. Contraindications—Surgical treatment is contraindicated when the patient's clinical status prevents surgical treatment.

 

c. Procedures

 

i. An arthrotomy is performed to remove all the purulent fluid and irrigate the joint.

 

ii. For the hip, an anterolateral or medial approach is performed emergently to decrease the risk of developing osteonecrosis.

 

iii. Joints like the shoulder, elbow, knee, and ankle can be drained open or with an arthroscope.

 

d. Rehabilitation—Patients may start ROM exercises in the first few days after surgery.

 

E. Complications

 

1. Complications of septic arthritis are joint contracture, hip dislocation, growth disturbance, limb-length discrepancy, joint destruction, gait disturbance, and osteonecrosis.

 

2. The risk of meningitis is highest with H influenza infections.



III. "Special" Infections

A. Neonates

 

1. Overview

 

a. Neonates younger than 8 weeks of age deserve special consideration because their immune systems are immature.

 

b. Neonates are more susceptible to infection and often do not manifest the symptoms and signs that normally assist in diagnosis.

 

2. Patient groups

 

a. Neonatal intensive care unit (NICU) infants

 

i. NICU infants are at risk for infection because of phlebotomy sites, indwelling catheters, invasive monitoring, peripheral alimentation, and intravenous drug administration.

 

ii. Multiple sites of infection are present in 40% of NICU infants with musculoskeletal infection, typically due to S aureus or gram-negative organisms.

 

b. Otherwise healthy infants who develop an infection between 2 and 4 weeks of age at home

 

i. Group B streptococcus is usually the causative organism.

 

ii. Usually only one site is involved.

 

c. Patients with Kingella kingae septic joints have fewer systemic signs and less joint irritability than do those with septic joints due to other organisms.

 

3. Anatomy

 

a. Before the secondary center of ossification appears, the metaphyseal vessels also supply the epiphysis, so osteomyelitis in the metaphysis often (76% of cases) spreads to the epiphysis and the adjacent joint.

 

b. Growth disturbance and physeal arrest can occur.

 

4. Diagnosis—Diagnosis in the neonate can be difficult.

 

a. Fever is usually absent.

 

b. Early signs are pain with motion, decreased extremity use, pseudoparalysis, difficulty feeding, and temperature instability.

 

c. Tenderness, swelling, and erythema occur later.

 

5. Laboratory findings

 

a. The WBC is usually normal.

 

b. Blood cultures are positive in 40%, and the ESR may be elevated.

 

c. For K kingae, the yield of positive cultures is higher if the sample is sent in a blood culture bottle. These should be used if there is a sufficient amount of specimen.

 

6. Treatment

 

a. Neonates with documented sepsis should have aspiration and culture of all suspicious areas.

 

b. Positive areas should be surgically drained, with care taken to avoid additional damage to growth centers.

 

B. Shoe puncture—Shoe punctures can cause a simple laceration, cellulitis, septic arthritis, or osteomyelitis.

 

1. When an object has penetrated a sneaker, Pseudomonas is an organism of concern, although infection by S aureus is more common.

 

2. Tetanus status should be ascertained and coverage provided if deficient.

 

3. Radiographs should be taken to look for a retained foreign body.

 

4. Initial treatment

 

a. Initial treatment is soaks, elevation, rest, and antibiotic therapy that cover both S aureus and Pseudomonas.

 

b. A poor response to this regimen indicates a more extensive problem.

 

5. Bone scan or MRI can help diagnose more complex infections requiring surgical debridement.

 

6. Superficial infections occur in 10% to 15% of children following shoe puncture wounds, and deep infection in approximately 1%.

 

7. Surgery is indicated for a foreign body, abscess, septic arthritis, or failure to respond to antibiotics.

 

8. Late, deep infections are due to Pseudomonas in >90% of cases.

 

C. Diskitis

 

1. Diskitis usually occurs in children younger than 5 years.

 

2. The infection starts in the vertebral end plates and moves to the disk through vascular channels.

 

3. S aureus causes most cases.

 

4. Blood cultures should be obtained, but local cultures are not routinely needed.

 

5. Patients present with low-grade fever, limp, or refusal to bear weight; the child refuses to move the spine.

 

6. Plain radiographs are normal for the first 2 to 3 weeks, but they may show loss of the normal sagittal contour early; bone scan or MRI confirms the diagnosis earlier.

 

7. Antibiotics successfully treat most cases; patients who do not respond to antibiotics should have a biopsy.

 

D. Vertebral osteomyelitis

 

1. Vertebral osteomyelitis affects older children.

 

2. More constitutional symptoms are usually present with vertebral osteomyelitis than with diskitis, and there is more focal tenderness on examination.

 

3. MRI or bone scan is sensitive early; plain radiographs show bone destruction later.

 

4. Treatment with antistaphylococcal agents is curative.

 

E. Sacroiliac infections

 

1. Infections of the sacroiliac joint cause fever, pain, and a limp.

 

2. Patients have pain with lateral compression of the pelvis, the FABER hip test, and tenderness over the sacroiliac joint.

 

3. MRI is the most sensitive test.

 

4. Initial antibiotic treatment should cover S aureus, the most common cause.

 

5. If aspiration or drainage is necessary, it can usually be done with CT guidance.

 

F. Sickle cell disease

 

1. Children with sickle cell disease are at increased risk for both septic arthritis and osteomyelitis.

 

2. The frequent bone infarcts, sluggish circulation, and decreased opsonization of bacteria all contribute to the susceptibility.

 

3. S aureus and Salmonella are the most common organisms, so initial antibiotic treatment should cover both.

 

4. Differentiation between sickle cell crisis and infection can be challenging.

 

a. Both entities may cause fever, pain, tenderness, swelling, and warmth.

 

b. The WBC, CRP, and ESR may be elevated in both.

 

c. Bone scan and MRI are often not specific as well.

 

5. Only approximately 2% of children with sickle cell disease admitted to a hospital with musculoskeletal pain have osteoarticular infection.

 

6. A positive blood culture or a positive osteoarticular aspirate is diagnostic.

 

G. Notable organisms

 

1.

Tuberculosis

a. The incidence of TB has been rising in developed countries over the past 30 years because of immunocompromised patients and the emergence of multidrug-resistant strains.

 

b. Children are more likely to have extrapulmonary involvement, with bone and/or joint involvement occurring in 2% to 5% of children with TB.

 

i. The most common sites of musculoskeletal involvement are the spine (50%), large joints (25%), and long bones (11%).

 

ii. Polyostotic involvement has been reported in 12%.

 

c. Presentation

 

i. Patients can present with fever, night sweats, weight loss, and pain.

 

ii. Patients with skeletal infections, however, may have more subtle findings, with absence of fever, only mild pain, and normal blood studies.

 

d. In the spine, the anterior one third of the vertebral body is usually involved, most often in the region of the thoracolumbar junction; a paravertebral abscess may cause neurologic deficits.

 

e. Long bone lesions are radiolucent, with poorly defined margins and surrounding osteopenia.

 

f. The hip and knee are the joints most commonly affected. Involved joints have diffuse osteopenia and subchondral erosions.

 

g. Laboratory findings—The WBC is normal, the ESR is usually elevated, and the purified protein derivative test (PPD) is usually positive.

 

h. A biopsy with stains and culture for acid-fast bacilli is diagnostic.

 

i. Treatment is usually medical, for at least 1 year.

 

i. Surgical debridement of long-bone lesions may hasten resolution of constitutional symptoms, but incisions should be closed to avoid chronic sinus formation.

 

ii. Drainage and stabilization of spine lesions is indicated for neurologic deficits, instability, progressive kyphosis, or failure of medical therapy.

2.

Lyme disease

a. Epidemiology

 

i. Lyme disease is infection caused by Borrelia burgdorferi, which causes erythema migrans, intermittent reactive arthritis, neuropathies, cardiac arrhythmias, and occasionally an acute arthritis.

 

ii. The infection is caused by a bite from the deer tick, which is prevalent in New England and the upper Midwest.

 

b. History and physical examination

 

i. The arthritis is generally less painful than bacterial arthritis. Patients can present with fever and a swollen, irritable joint but will still bear weight.

 

ii. Erythema migrans is the rash typically seen after infection with B burgdorferi, although it is not always present. Classically, it is an expanding, "bulls-eye" rash.

 

c. Laboratory findings

 

i. The WBC may be normal or elevated, but the ESR and CRP are usually elevated.

 

ii. Joint aspirates have a markedly elevated WBC count.

 

iii. Serologic testing is positive for B burgdorferi.

 

iv. The rapid Lyme immunoassay should be included in the septic joint evaluation in endemic areas.

 

d. The factors most helpful to differentiate between bacterial arthritis and Lyme arthritis are the ability to bear weight and a normal serum WBC with the latter.

 

e. Lyme arthritis is treated with antibiotics, including doxycycline, amoxicillin, and cefuroxime.

4.

Gonococcal arthritis

a. Gonococcal arthritis is caused by a Neisseria gonorrhea infection. It affects sexually active adolescents, sexually abused children, and neonates with infected mothers.

 

b. Because of the association with sexual abuse, children with a suspected infection should have cultures taken of all mucous membranes.

 

c. The knee is most commonly involved, but the infection is polyarticular in 80% of cases.

 

d. N gonorrhea is difficult to culture, so synovial aspirates should be cultured on chocolate blood agar.

 

e. Treatment is usually medical in confirmed cases. Typical antibiotics include ceftriaxone or cefixime because of the increased prevalence of penicillin-resistant organisms.

 

f. Arthrotomy is required for hip infections, but other joints can be observed or treated with serial aspiration.

4.

Coccidiomycosis

a. Coccidioides immitis is a fungus endemic to the Southwestern United States that can cause a polyostotic osteomyelitis in affected individuals.

 

b. The infection starts as an upper respiratory infection but can progress to disseminated disease in a small percentage of patients. Diagnosis is usually delayed.

 

c. The WBC and ESR are often normal.

 

d. In addition to antifungal medical therapy, surgical debridement is usually required to eradicate the infection.

 

IV. Chronic Recurrent Multifocal Osteomyelitis

A. Overview

 

1. Diagnosis of chronic recurrent multifocal osteomyelitis (CRMO), an idiopathic inflammatory disease of the skeleton, is a diagnosis of exclusion.

 

2. CRMO is characterized by a prolonged course with periodic exacerbations.

 

3. When there is associated synovitis, acne, pustulosis, hyperostosis, and osteitis, the condition is called SAPHO syndrome.

 

4. The condition is characterized by periods of exacerbation, but usually goes into remission after 3 to 5 years.

 

5. The incidence is unknown.

 

6. CRMO occurs primarily in children and adolescents and is more common in girls; the peak age of onset is 10 years.

 

7. The metaphyses of long bones and the clavicle are most commonly involved. Clavicle involvement is common in CRMO, unlike in true infections.

 

B. Pathoanatomy

 

1. The pathophysiology is unknown.

 

2. Theories include an infection by an organism with fastidious growth requirements, or an auto-immune disorder.

 

C. Evaluation

 

1. History—Patients have insidious onset of episodic fever, malaise, local pain, tenderness, and swelling.

 

2. Physical examination

 

a. Patients have swelling and point tenderness over the involved bones.

 

b. They may have low-grade fever.

 

3. Laboratory findings

 

a. The WBC is usually normal.

 

b. The ESR and CRP may be elevated.

 

c. Bone cultures are negative.

 

4. Diagnostic imaging

 

a. Plain radiographs show eccentric metaphyseal lesions with sclerosis, osteolysis, and new bone formation that frequently is symmetric.

 

b. Bone scan helps identify all the sites of involvement.

 

c. Because of the shared characteristics between CRMO and malignancy, MRI is helpful to judge the extent and the soft-tissue involvement of the lesion.

 

D. Treatment

 

1. Nonsurgical

 

a. Although many children have biopsies and local cultures at the time of initial presentation to establish the diagnosis, treatment is always nonsurgical once the diagnosis is established.

 

b. Scheduled nonsteroidal anti-inflammatory medications during exacerbations successfully manage the symptoms in 90% of patients.

 

2. Surgical—Surgery is indicated only when a biopsy is needed to establish the diagnosis.



Top Testing Facts

Acute Hematogenous Osteomyelitis

1. A child with bone pain and fever should be assumed to have osteomyelitis until proven otherwise.

 

2. AHO without abscess can generally be treated medically.

 

3. In areas with a high prevalence of CA-MRSA, surgical drainage may be necessary even in the absence of documented abscess on imaging studies.

 

4. If the response to antibiotics is poor, preoperative MRI aids surgical planning by delineating the extent of the infection and the location of abscesses.

 

5. Most cases of AHO are caused by S aureus.

 

6. Because of the prevalence of CA-MRSA, empiric coverage should cover CA-MRSA in most (if not all) cases.

 

7. Susceptibilities and resistant strains of CA-MRSA vary by community, adding importance to aspiration or biopsy for culture.

 

8. The metaphyseal blood supply crosses the physis to the epiphysis in children younger than 12 to 18 months, so severe sequelae are more common.

 

9. In neonates, the most common organism is group B streptococci.

 

Subacute Osteomyelitis

1. Subacute osteomyelitis may be indistinguishable from tumors on radiographic studies.

 

2. Surgery is most commonly required in cases of subacute osteomyelitis.

 

Septic Arthritis

1. Septic arthritis more commonly occurs in younger children, with 50% of cases in children ≤2 years old.

 

2. Septic arthritis is a surgical emergency.

 

3. When managing the hip, err toward drainage in equivocal cases; the morbidity of an arthrotomy is minimal compared to the sequelae of a neglected septic hip.

 

4. Kingella kingae infections tend to have more subtle findings—fewer systemic signs and less impressive joint irritability.

 

5. If there is sufficient fluid from arthrocentesis, a portion of the sample should be placed in a blood culture bottle because K kingae grows more readily in this medium.

 

6. Children with septic arthritis appear sicker and are in more distress than those with toxic synovitis.

 

7. Children with synovitis appear comfortable and may be playful if the hip remains still.

 

8. Check the child's immunization status to see if H influenza coverage is necessary during empiric therapy.

 

9. Juvenile rheumatoid arthritis rarely presents in the hip.

 

Special Infections

1. Of NICU babies with musculoskeletal infection, 40% have multiple site involvement.

 

2. Infections in infants frequently cross the physis, with resultant infection of the metaphysis and adjacent joint.

 

3. Following nail puncture through a shoe, soft tissue infection occurs in 10% to 15% of cases and deep infection in 1%.

 

4. Pseudomonas accounts for more than 90% of late deep infections following nail puncture through sneakers.

 

5. S aureus and Salmonella are the most common infecting organisms in children with sickle cell anemia with musculoskeletal infection.

 

6. In children with TB, the most common sites of musculoskeletal infection are the spine (50%), large joints (25%), and long bones (11%). Polyostotic involvement occurs in 12%.

 

7. Lyme disease is often heralded by the typical skin lesion, erythema migrans.

 

Chronic Recurrent Multifocal Osteomyelitis

1. CRMO is a diagnosis of exclusion.

 

2. Cultures are negative in CRMO.

 

3. Unlike true infections, involvement of the clavicle is common in CRMO.



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