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 
is drawn.
     1)  What is your current diagnosis and management 
plan ?
     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.

View landmarks.

     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 
very important.

     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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Web Page Author:
Loren Yamamoto, MD, MPH
Associate Professor of Pediatrics
University of Hawaii John A. Burns School of Medicine