Hot Seat #76: 3 yo with a swollen knee
Posted on: May 31, 2016, by : Caleb Ward MD
Caleb Ward, Children’s National Medical Center
with Asha Payne, Children’s National Medical Center
The Case
A 3 year-old previously healthy boy presents to your ER in April in a mid-Atlantic state with one day of tactile fever and right knee swelling. The family had noted he appeared to be limping but was still able to walk. He had otherwise been well with his usual activity levels. They denied any preceding trauma.
ROS:
+ Fever, itchy rash to face and extremities, slightly decreased PO intake
– Easy bleeding or bruising, no vomiting or apparent abdominal pain, no facial asymmetry
PMH, PSH, FH, SHx all noncontributory
PE: T 38.0, HR 120, RR 24, BP 115/69, SpO2 100% RA
Well appearing, sat on bed, smiling and playing with book
Fine sandpaper rash over face and anterior chest
Chest CTAB, regular rate and rhythm, no murmur, cap refill < 2s
Right knee is grossly swollen with presumed effusion, tolerates flexion to 90 degrees, internal/external rotation of hips nontender, will weight bear but limps, normal spinal exam
Initial labs:
ESR 84mm/hr
CRP 3.49 mg/dL
WBC 12.1, Hgb 12.2, Plt 274
Lyme titres have also been sent.
Plain films of the knee reveal: moderate suprapatellar joint effusion and soft tissue swelling of the knee without evidence of fracture or dislocation. Point of care US confirms a joint effusion.
You give a dose of Motrin and his temperature drops to 36.8; he appears more comfortable and can walk, though still with a slight limp.
Question 1:
After discussion with Orthopedics you decide to perform a joint aspiration. Your analgesic/sedative plan for the patient will include: local infiltration of lidocaine, use of child life and a papoose.
Question 2:
You perform the aspiration and obtain 40cc of thick cloudy fluid. Cytology: WBC 35000 WBCs (94% segs), 2000 RBCs. Culture of the joint fluid is pending.
Question 3:
You decide to defer further imaging pending his clinical course.
Question 4:
How would you approach this case? Please share your opinions by clicking on “What do you think?” below.
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Although I think the kid will likely be treated presumptively for Lyme arthritis, remember that post-streptococcal infection can also mimic septic arthritis and Lyme arthritis. The kid presented with a scarletiniform rash, fever, and decreased POs (perhaps from a sore throat!).
Although synovial WBC counts are not perfectly reliable (but what diagnostic test is?!), having <50K cells is somewhat reassuring that this is not septic arthritis. Also, I presume that the gram stain was negative (which is not that sensitive), but when positive does typically clench the diagnosis of septic arthritis.
There is no rush to wash out a knee joint as there is for a hip joint where the pressure builds up more quickly and can literally melt away the cartilage. With a synovial WBC of only 35K, I doubt the orthopedic surgeons would even wash out this acute, monoarticular arthritis of the knee.
I agree with Dewesh. Additionally, this is a kid I would make sure had close followup with his PMD, making sure to speak to the PMD around the time of discharge.
With regards to the management questions posed:
1. We need to make sure that “consult ortho” is not code for “I think this joint needs to be tapped, but I don’t want/feel comfortable to tap joints.” We have the luxury of in-house Ortho, which on a very busy day, can be helpful, but we shouldn’t be hesitant to practice the procedures in our repertoire. That said, it is very appropriate to involve them in the care of this patient.
2. Although not provided as an option, I would include child life (if available). In addition to helping the child (and parents!) cope with a procedure, they may give you some clues as to whether the kid would benefit from sedation.
Excellent comments. We always discuss what a consultant would do given the story you tell them. In reality if you think you know, you should just do it. Knee arthrocentesis is not difficult and between child life, visual barriers and midaz-mataz for small children, it can be done without much hassle. Ultrasound is also helpful.
Lyme is endemic in the Mid Atlantic region and it feels as though Lyme arthritis here is quite common. Dewesh mentioned strep is possible, wonder if JRA should be on the differential. Knee washouts will be ortho’s call unless you have frank pus, or the pt is diabetic (my General EM hat showing through). Doxy is a great medication for those who are amoxicillin allergic, regardless of tooth enamel.