Aspirating the Ankle Joint
Radiology Cases in Pediatric Emergency Medicine
Volume 3, Case 6
Lynette L. Young, MD
Kapiolani Medical Center For Women And Children
University of Hawaii John A. Burns School of Medicine
A 2-year old male was playing indoors three hours
ago. His mother noticed that he was not walking and
he began to complain of right leg pain. There was no
history of trauma. He did have a cold for the last week
and had a fever. His highest temperature measured at
home was 40.5 degrees. The patient was seen in his
pediatrician's office earlier in the day for fever and was
prescribed amoxicillin for an ear infection. The patient
returned the pediatrician's office later in the afternoon
because he was refusing to walk. There is no history of
sore throat or rash. The patient was sent to the ED for
further evaluation. His past medical history is
Exam: Vital signs T38.1 (tympanic), P193, R28,
BP 127/85, O2sat 99%(RA), Wt13.4kg (75%ile). He is
alert and is being carried by his mother. His left lower
extremity is nontender with full range of motion of his
left hip, knee, and ankle. His right hip, femur, knee,
proximal tibia and fibula, and foot are nontender. There
is normal range of motion of his right hip and knee.
There is reproducible point tenderness over the right
anterior ankle joint, possibly the talus. There is pain
elicited with right ankle range of motion. There is no
swelling, overlying skin lesion, erythema, or asymmetric
warmth. Pulses are good. Toes are pink.
Radiographs of his right hip, knee, leg, ankle and
foot are obtained.
View ankle and foot radiographs.
His hip, knee, and leg radiographs are normal. They
are not shown here. His ankle and foot radiographs do
not reveal any fractures, foreign bodies, or lytic lesions.
There is no periosteal elevation noted.
Laboratory results: CBC WBC 26.1, 2% bands,
75% segs, 19% lymphs, 4% monos, Hgb 11.8, Hct
34.1, platelet count 381,000. ESR 25. A blood culture
1) What is your current diagnosis and management
2) Would you consider hospitalizing him at this point
or starting him empirically on a different oral antibiotic
and discharging him home ? In summary, this child has
a high fever and is refusing to bear weight. He has
tenderness on range of motion about the right ankle
and reproducible point tenderness over the anterior
aspect of the ankle. He has a high WBC, but only a
modestly elevated sedimentation rate.
3) Specifically, would you consider performing a
bone scan, an ankle arthrocentesis, or a bone
aspiration at this point ?
This patient arrived in the E.D. in the evening. A
bone scan may take several hours to perform. It is not
easily performed in the evening in most small hospitals.
In this case, it would have to wait for the morning.
A right ankle arthrocentesis is performed. The
patient is given IV midazolam and morphine. One mL
of buffered 1% lidocaine is used for local anesthesia.
The ankle is aspirated with an 18 guage needle.
See results of aspiration.
Three mL of purulent yellow fluid is aspirated. The
fluid is sent for culture, cell count, and gram stain.
He is given oxacillin intravenously. Laboratory studies
performed on the arthrocentesis fluid: WBC 22,100,
2% bands, 78% segs, 6% lymphs, 14% monos, RBC
373,000. Gram stain: many WBC's, no organisms.
The patient is hospitalized for intravenous antibiotics
for septic arthritis. The next day, the culture of the
ankle joint aspirate is positive for Streptococcus
pneumoniae. He has a bone scan which shows
increased uptake of the right talus. He undergoes a
right ankle arthrostomy, synovial biopsy, curettage and
windowing of the talus for septic arthritis AND
osteomyelitis. He has a Penrose drain placed. A
repeat ESR is 40. The blood culture is negative. The
right ankle surgical wound heals well without
Aspirating the ankle joint:
Identify two landmarks, the medial malleolus and the
thick anterior tibial tendon. The anterior tibial tendon
can be palpated easily with dorsiflexion. It is located
about 1 cm anterolateral to the medial malleolus.
The arrows on the adult's foot photographed here
point to the anterior tibial tendon. In most patients, this
may not be as easy to see as in this photo, however,
locating this tendon by palpation is usually not difficult
when asking the patient to DORSI flex against force.
The anterior margin of the medial malleolus is also easy
to locate. These landmarks are shown on our 2-year
old patient's ankle as two vertical marks (right image).
The lateral mark (lighter) is drawn over the anterior tibial
tendon and the medial mark (darker) is drawn over the
anterior margin of his medial malleolus. Have the
patient supine with the foot in slight PLANTAR flexion.
Plantar flexion opens the ankle joint space wider.
View joint space.
Notice how the joint space is relatively closed in
dorsiflexion and more open in plantar flexion. Plantar
flexion optimizes needle entry into the joint space.
The puncture site is between the two landmarks.
Prep the area with povidone-iodine solution, and
anesthetize the skin with 1% lidocaine. To aspirate,
have an 18 or 20 gauge needle with a 10 ml syringe.
Insert the needle medial to the anterior tibial tendon and
aim toward the anterior edge of the medial malleolus.
Aspirate the fluid in the joint space.
Teaching points and Discussion:
1. Septic arthritis (infection within a joint space) is
often difficult to diagnose early in its course. It is
frequently not diagnosed on the first visit. There must
be a high index of suspicion to make the correct
diagnosis. It is essential to recognize septic arthritis
early because a delay in the diagnosis and treatment
can lead to serious complications. Septic arthritis is a
condition that urgently requires intravenous antibiotics
and sometimes open drainage. Serious complications
include joint destruction and long term disability.
2. Septic arthritis is more common in children than
in adults. Most of the cases occur in children less than
5 years old. The highest incidence occurs in children
between 6 months and 24 months of age. Males
outnumber females 2:1.
3. Predisposing factors include significant trauma
(in 30% to 45% of cases), preceding upper respiratory
infection, and otitis media. Less frequently there could
be an associated skin or soft tissue infection. Often
there are no preceding factors identified.
4. There are three mechanisms by which the
organism can enter the joint space. The most common
mechanism in children is hematogenous spread.
Rarely there could be direct inoculation or extension
from a contiguous site of infection. With the bacteria in
the joint space there is a subsequent inflammatory
response. There is neutrophil infiltration and the
purulent material accumulates within the joint space.
The direct pressure as well as proteolytic enzymes
cause the symptoms of tenderness, swelling, and
5. The organism most frequently found in septic
arthritis varies with age. In the neonatal period (first 2
months of life), the most common organisms are group
B Streptococcus and Staphylococcus aureus. There
also may be gram negative enteric organisms. Beyond
the neonatal period up to 2 years of age the most
common organisms have been Hemophilus influenzae
and Staph aureus. The frequency of H. influenzae has
decreased because of the ubiquitous use of H. flu
vaccine. In the 2 to 5 year old age range the most
common organisms have been H. influenzae, S.
aureus, group A Streptococcus, and Streptococcus
pneumoniae. In children older than 5 years old the
most frequent organism is S. aureus. In sexually active
adolescents, Neisseria gonorrhea has also been
implicated as an etiology of septic arthritis.
Pseudomonas aeruginosa is associated with puncture
wounds. In patients with sickle cell anemia, Salmonella
species may be recovered in the culture. Frequently
there is no organism recovered in patients diagnosed
with septic arthritis (up to 30%).
6. The most common joint involved in children is the
hip, followed by the knee and then the ankle joint. Less
frequently the site is a joint in the upper extremity
elbow, shoulder, or wrist. Since a joint in the lower
extremity is the more common site, the patient often
presents with a limp or a refusal to walk. Occasionally
more than one joint is involved (6-11%).
7. Common symptoms include erythema, swelling,
tenderness and lack of active motion at the affected
joint. The signs are often subtle, especially in the
neonates. Fever of greater than 38.3 is found in about
75% of the patients.
8. The WBC count in septic arthritis is variable. In
most patients there is a leukocytosis with a shift to the
left, but about 50% of patients will have a WBC count
less than 15,000/cu mm. A normal white count does
not rule-out septic arthritis. The ESR and CRP are
more frequently abnormal in patients with septic
arthritis. The ESR is elevated in about 90% of the
cases. Although this test is more sensitive than the
WBC count, it is nonspecific. The ESR may be
elevated in many other conditions. Blood cultures are
positive in about 40% of the cases, more frequently if
the organism is H. influenzae. Radiographs are
recommended although they are usually normal in early
septic arthritis. Late findings may include joint widening
and bony destruction. There is no laboratory test or
X-ray that can rule-out septic arthritis. The joint fluid
must be analyzed if there is any suspicion of septic
9. The joint fluid should be sent for WBC count,
gram stain and culture, and glucose. The WBC count is
usually greater than 50,000 cells/cu mm, with a
predominance of neutrophils (>75%). There have been
cases of septic arthritis with the WBC count as low as
5,000 cells/cu mm. The glucose is usually less than 40
mg/dL. The joint fluid culture is positive in about 60% of
cases. If an organism is recovered it is most frequently
found in the joint fluid, therefore an arthrocentesis is
1. Dufort JE, Smith-Wright D. Septic Arthritis. In:
Barkin RM (ed). Pediatric Emergency Medicine
Concepts and Clinical Practice. Chicago, Mosby Year
Book, 1992, pp. 949-952.
2. Fleisher GR. Septic Arthritis. In: Fleisher GR,
Ludwig S (eds). Textbook of Pediatric Emergency
Medicine, third edition. Baltimore, Williams and Wilkins,
1993, pp. 638-639.
3. Kobernick M. Arthrocentesis. In: Roberts JR,
Hedes JR (eds). Clinical Procedures in Emergency
Medicine. Philadelphia, W.B. Saunders Company,
1985, p 693.
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