Pediatric Examination and Board Review (110 page)

11.
A 13-year-old boy presents after spring break with a chief complaint of knee pain. He first noted the bilateral knee pain last summer, and it abated until recently. He denies playing any sports, but does perform in a hiphop dance group when on school vacations. He denies fever or any other symptoms. He is not sexually active and denies any trauma. On examination he has no trouble with ambulation, has no joint effusions, has full range of motion at the hip and knee, but complains of pain on palpation of the proximal tibia. What is the most appropriate next step in care?

(A) MRI of the knee

(B) plain films of the knee

(C) plain films of the hip

(D) arthroscopy

(E) reassurance and rest

12.
What is the most common cause of septic arthritis?

(A)
H influenzae

(B)
S aureus

(C)
E coli

(D)
Salmonella
species

(E)
M pneumoniae

13.
Which of the following is true regarding toddlers’ fractures?

(A) they result from major injury (eg, a fall from a great height)

(B) they are best seen on lateral radiographic view

(C) they occur in the distal third of the tibia

(D) they are best treated with rest and NSAIDs

(E) they are most commonly seen between 3 and 4 years of age

14.
In which of the following patients are radiographs not indicated with a clinical history and examination that is consistent with Osgood-Schlatter disease?

(A) atypical complaints of pain

(B) erythema or warmth over the tibia

(C) pain not directly over the tubercle

(D) bilateral pain and symptoms

(E) all require imaging

15.
What is the classic presentation of arthritis in a child with rheumatic fever?

(A) finger/joint involvement

(B) migratory among the large joints

(C) unilateral wrist

(D) bilateral ankle

(E) hip involvement

16.
Which is true of the treatment of toxic synovitis?

(A) antibiotics are the mainstay of therapy

(B) aggressive physical therapy should be initiated early

(C) joint aspiration is diagnostic

(D) NSAIDs are the initial therapy

(E) more than 50% will recur with or without therapy

ANSWERS

1.
(A)
Although a bone scan is useful in diagnosis of osteomyelitis, it is not an optimal choice for initial investigation of a joint effusion. Plain films are not sensitive initially for osteomyelitis and rarely assist in the diagnosis of a septic joint, but they will help to rule out more concerning diagnoses such as malignancies and detect any underlying fractures. A CBC with differential, ESR, and CRP are helpful inflammatory markers for diagnosis and to follow progression of the illness.

2.
(B)
The most worrisome diagnosis at this point is septic arthritis. Reactive arthritis and periarticular cellulitis must still be considered but are less likely. However, transient synovitis is most common in the hip. It can be differentiated from septic arthritis by laboratory results. Septic arthritis is more likely to have an increased leukocyte count with a left shift and an increased ESR and CRP. With these laboratory results, transient synovitis is highly unlikely.

3.
(D)
Although ultrasound will reveal an effusion, the presence of an effusion does not definitively diagnose septic arthritis. Analysis of fluid obtained from an aspiration would demonstrate a leukocytic effusion, thus differentiating it from noninflammatory causes of joint effusion. Aspirated joint fluid might reveal bacteria on Gram stain or culture.

4.
(E)
Although all the choices are morphologies of known causes of osteomyelitis, the most common cause is
S aureus,
gram positive organisms in clusters
. Salmonella
is common among patients with sickle cell anemia, and
Pseudomonas
may be the cause following puncture wounds. The gramnegative coccobacillus
Kingella kingae
is an emerging cause of osteomyelitis in Israel, but it is far less common than
S aureus
.

5.
(A)
Although all the choices would provide some coverage for
S aureus
, it is important to cover the most important etiologies and resistant organisms well. In regions that have a high prevalence of MRSA, oxacillin, nafcillin, and related compounds would no longer be appropriate empirical choices. In such areas, clindamycin would be an appropriate agent. Ceftriaxone might be a reasonable addition if the patient has known or suspected sickle cell anemia because
Salmonella
osteomyelitis can occur in these patients as well as
S aureus
.

6.
(D)
Biopsy of the metaphysis of the affected bone is the most specific way to diagnose osteomyelitis, although it is not often performed. MRI and bone scan are 80-100% sensitive, but specificities can be lower than 50%. However, they are the preferential diagnostic imaging tools, especially in the absence of surgical aspiration, or to locate the area of inflammation. CT will probably not be helpful. Plain films can demonstrate evidence of osteomyelitis, but only after 10-14 days of infection.

7.
(C)
Hematogenous spread is the most common pathogenic mechanism in children. The vascularization of the metaphysis allows for bacterial seeding of the marrow cavity. Inflammation ensues and increases intraosseous pressure, which in turn hampers normal bone circulation. This can lead to necrosis and potential spread of infection to the epiphysis and joints. Direct invasion of bacteria into bone occurs in children but is most often secondary to trauma.

8.
(E)
All of these are potential complications of osteomyelitis. Septic arthritis can often result from contiguous spread of osteomyelitis. Hyperemia around the area of inflammation can lead to leg lengthening; proliferating cartilage can lead to leg shortening. Fractures can result from local destruction.

9.
(D)
Although all of the above joints may become infected, the most common site in older children (>1 year) is the knee. The hip is the most common site in younger infants.

10.
(E)
Although culture is key to identification of the causative organism, a blood culture is positive in no more than 50% of patients, and joint fluid culture is positive in 35-80% of patients. Fluid analysis is more immediately helpful in the diagnosis of septic arthritis: WBC higher than 100,000, depressed glucose levels, and increased lactic acid and lactate dehydrogenase (LDH) are the key findings. Although synovial fluid is essential to obtain, in extremely ill patients, treatment should not be delayed because one-third of joint cultures and nearly one-half of blood cultures remain positive even after initiation of antibiotics.

11.
(E)
The most likely diagnosis is Osgood-Schlatter disease (see
Figure 67-1
). With the patient’s history of recurrence during periods of increased activity, the best treatment for the patient is rest and NSAIDs as needed. A radiograph of the knee is reasonable if atypical clinical features are present.

FIGURE 67-1.
Osgood-Schlatter disease. The radiograph would show characteristic fragmentation of the tibial tubercle apophysis, similar to the diagram. (Reproduced, with permission, from Skinner HB. Current Diagnosis & Treatment in Orthopedics, 4th ed. New York: McGraw-Hill; 2006: Fig. 11-29.)

12.
(B)
The leading cause of septic arthritis in children is
S aureus. H influenzae
type b was an important cause in infants and children before the introduction of immunization.
Salmonella
,
E coli
, and
M pneumoniae
rarely infect joints.

13.
(C)
Toddlers’ fractures are commonly seen between 9 months and 3 years as a result of minor falls, trips, or twists. The children present with inability to weight-bear and pain on dorsiflexion of the ankle. On internal oblique view, the fracture is most often noted in the distal third of the tibia. A fracture that is in the midshaft would be far more suggestive of abuse. Toddlers’ fractures should be casted for 5-6 weeks. This diagnosis should always be considered in a limping child of this age.

14.
(D)
Bilateral disease is commonly seen in Osgood-Schlatter and should not in and of itself prompt further imaging. The remaining choices are all suggestive of some other pathology and warrant further radiologic investigation.

15.
(B)
The classic presentation of rheumatic fever is that of a child with migratory polyarthritis in large joints. Although smaller joints (including wrist and hand) can be involved, they are more often one of many joints involved. Most patients have large joints involved first.

16.
(D)
Toxic synovitis, a diagnosis of exclusion, is best treated with rest and NSAIDs. Antibiotic therapy would be appropriate for septic arthritis diagnosed by aspiration but not for toxic synovitis.

S
UGGESTED
R
EADING

Jung ST. Significance of laboratory and radiologic findings for differentiating between septic arthritis and transient synovitis of the hip.
J Pediatr Orthop.
2003;23:368-372.