Alright, today we're gonna talk about the most
common cause of joint pain, osteoarthritis.
Here's a case.
A 52-year old man presents with
acute-on-chronic right knee pain.
Now he has intermittently had knee pain
for about 5 years, worse after activity,
with morning stiffness for
up to 15 minutes everyday.
This past Saturday, he spent much of the day
helping his son move into his college dorm
and the next morning, he reports that
his right knee is swollen and painful.
Denies any fevers or chills, no other involved joints,
his pain is worst at the medial aspect of the knee.
Initial vitals, completely unremarkable and on gross
inspection we see symmetric, bony enlargement of the knees.
On range of motion testing, his right knee
is limited to about 90 degrees of flexion.
It's limited by pain and stiffness and
you do note some crepitus on exam.
On palpation of the right knee,
we find a tender medial joint line,
no pain over the pes anserine bursa, no increased
warmth and a small effusion is present.
Alright, so let's highlight some of
the important features of this case.
It sounds like this is an
acute on chronic issue.
He's had pain for 5 years but something seems
to have made it worse over the past day or so.
The pattern of joint
involvement is also important.
It sounds like it's asymmetric, it's mostly involving
just one knee and of course it's monoarticular.
Next stop in terms of
well, on the one hand we have
swelling and we have a painful joint
which tends to make us think of joint inflammation
or probably end up of having to get an arthrocentesis
to see how inflamed
this joint really is.
And then next stop,
Well, review of systems is
We're not getting any fevers or any
evidence of any other systemic illness.
So, I think we could say there
is no systemic involvement.
So, with that history in mind,
what is the most likely diagnosis?
Let's start with pseudogout.
Pseudogout as you may recall is also
CPPD, calcium pyrophosphate deposition
and it is a relatively common
type of crystalline arthropathy.
Most importantly, the most common
joint affected in CPPD is the knees.
Now, we'd wanna ask about some other
common risk factors for pseudogout
like hyperparathyroidism, hemochromatosis,
I'd like to think of that as iron-hyper-iron
and then hypomag or
Of course, only in arthrocentesis is really gonna
help us to include or exclude that diagnosis.
We'll keep a question
mark there for now.
And then, osteoarthritis.
As I've said at the beginning of this talk, it's the most
likely diagnosis 'cause it's the most common cause of pain.
Typically you can have an acute-on-chronic
picture, knee involvement is very common
and even this description of bony enlargement of the
bilateral knees leads us towards that diagnosis.
But what about this
Can that happen with osteoarthritis?
I think we'll have to leave a
question mark in that box for now.
Next stop, rheumatoid arthritis.
Now, we need to consider rheumatoid arthritis though there
are some things that are gonna conflict with that diagnosis.
First of all, it's monoarticular.
We tend to expect to have symmetric
findings, you expect to see more stiffness,
he's saying he's only stiff for 15 minutes in the morning,
we'd wanna see stiffness for 30 minutes to nearly an hour
and also we don't have any
systemic symptoms at all.
The effusion, however, would be pretty
typical with rheumatoid arthritis,
so, I think we'll just keep that
on the list for now as well.
Next stop is patellar
Now remember, patellar tendinopathy
is also known as "jumper's knee".
It's basically inflammation, swelling and
even potentially thickening of the tendon
that attaches the distal patella to the tibial
tuberosity as shown in this image here.
It's typically an overuse
injury most common in athletes.
It would typically cause anterior knee
pain rather than medial knee pain
and it would be pretty unusual
in a middle-aged non-athlete.
So, I think it's safe for us
to take that one off the list.
Next stop, pes
Now, there are several bursa, it can get
kind of complicated that surround the knee.
Including, shown here, the suprapatella,
the prepatellar, the infrapatellar bursa.
In addition, not depicted here because of the
plane of this image, is the pes anserine bursa
which lies just distal to the medial
joint line of the knee on both sides.
The bursa in general serve as soft buffers
between tendons and hard bony surfaces,
from wear and tear.
When they become inflamed from overuse,
occasionally from immune mediated inflammation
and more rarely from infection, the bursa can become
exquisitely painful, swollen and warm to the touch.
Now as I've said, the pes anserine bursa is medially
located, which is where our patient is experiencing pain,
but again, it's about 2 cm distal from the medial
joint line, distal to the medial tibial plateau.
So really a good physical exam should be
able to distinguish between tenderness
at the medial joint line versus tenderness
distal to that at the pes anserine bursa
and we were given a
pretty thorough exam.
So I think we can safely rule out
pes anserine bursitis as well.
So, we're left with pseudogout,
osteoarthritis and rheumatoid arthritis.
Looks like we're gonna need an
orthocentesis to tease these apart.
Okay, so here's our results.
No crystals, that's reassuring.
Cell count is 1,300 nucleated
cells and gram stain is negative.
Culture is no growth in case we're
ever considering aseptic arthritis.
Let's look at that cell count and
try and put that into perspective.
So, here's a nice schematic showing how to
interpret the synovial fluid cell count.
It looks like our cell count of 1,300 is
gonna put us into the non-inflammatory column
here on the far left of the spectrum
which supports osteoarthritis after all.
Here's the key point.
While it's unusual to have acute synovitis with an
effusion like osteoarthritis, it definitely happens
and it can certainly look at first
like an inflammatory arthritis.
But the key clues here are a relatively
cool effusion which is how it was described
in our HPI compared with the hot effusion you
might see with septic arthritis or gout.
Also this patient had no systemic symptoms which would
lead us away with something like rheumatoid arthritis.
And lastly, this cell count of less than 2,000 is gonna
definitely push us into a non-inflammatory category.
Remember, things like gout are typically
gonna have 20 to 80,000 cells
and in septic arthritis is certainly gonna be more
than 50,000 cells potentially as high as 100,000 cells.
Alright, final point.
Bland synovial fluid with less than
2,000 cells, think osteoarthritis.