1. How to Interpret Knee Films
It’s just a simple hinge joint, but with
many complex problems!

2. Positioning
• So your patient comes in with a knee looking
like this…
• So you want to order some imaging for them…
• Well, what will radiology have to do?

3. Positioning
• There are 3-views, 4-views, wt-bearing, non-
wt-bearing, sunrise, etc.
• It is important to consider the mechanism
when considering the tests because the pt
might not be able to get into a position to
have the pictures taken…
Frank ED, Merrill's Atlas of Radiographic Positioning and Procedures, 2007
Wt-bearing P/A Standard A/P Standard lateral Tunnel view Sunrise view Merchant view

4. Views
• Sunrise: Best at evaluating the patella
• Tunnel: Best for evaluating intercondylar
notch
• Lateral: Best at identifying fat-fluid levels
(lipohemarthrosis) suggesting intra-articular
fractures

5. Know Your Rules
You DON’T need to get an Xray if…
Ottawa Knee Rules Pittsburgh Knee Rules
• Age 2-55 • No fall or blunt knee trauma
• No fibular head TTP • Age 12-50yo
• No isolated patellar TTP • Able to walk 4 weight
• Able to flex 90 degrees bearing steps in the ED
• Able to weight bear for 4
steps after injury and in ED
(regardless of limping)
Validated in children age 2-16 (Annals EM 42:1, 2003) More specific than Ottawa (Ann Emerg Med 32:8 1998)

6. Standard A/P View
• A/P and Lat (standard 2 view) is 79% sensitive for fxs
• Adding 2 oblique views (4-view) increases sensitivity to 85%

7. Standard Lateral View

8. Poor Image Acquisition
A good lateral film
should have…
• Overlapping femoral
condyles (unlike here,
red arrows)
• Fibula behind tibia
(unlike here, yellow
arrow)
• Patella should have
two hyperlucencies
on anterior and
posterior aspects
(here it just looks
weird)

9. Improved View
• This is the more
ideal lateral
• Note the
overlapping
condyles (red
arrows)

10. Common DOH findings…
“DOH”!!! 1. Knee dislocations are
The knee is the either there or they’re
perfect joint to apply not…
the “DOH” pneumonic
2. The occult fractures are
• Dislocations? most common: along the
• Occult fractures? tibial plateau, to the
• Half pathology? patella, or to the proximal
lateral tibia (Segond)
There is plenty of 3. The only half pathology is
minutia, but we are
responsible for the big the Maissoneuvre fx (see
stuff… ankle radiology)

11. Fracture Data
Relative frequencies of fractures Most frequently overlooked
to the knee in adults fractures in an ED
1. Patella (40%) 1. Tibial plateau (16%)
2. Tibial plateau (32%) 2. Radial head (14%)
3. Fibular head (9%) 3. Elbow – child (14%)
4. Distal femur (8%) 4. Scaphoid (13%)
5. Tibial spine (7%) 5. Calcaneus (10%)
6. Tibial tuberosity (2%) 6. Patella (6%)
7. Osteochondral junction 7. Ribs (4%)
(1%)
--Stiell 1996, Weber 1995, Bauer 1995 --Data from Freed and Shields 1984

12. The Patella
• Most common bony
element of the knee
injured (account for 1%
of ALL bony fractures)
• Most common in pts 20-
50yo, men>women 2:1
• Fracture usually
following direct trauma
or forceful quads Trochlear groove
contraction
• When evaluating for
TTP, avoid performing
the patellar grind test (is
diagnostic of
chondromalacia
pattelae, not fracture)

13. Patellar Fracture Classifications
From Hohl M, Johnson EE, Wiss DA.
Fractures of the knee, in Rockwood
CA Jr, Green DP, Bucholz RW (eds):
Fractures in Adults, 3d ed, vol. 2.
Philadelphia, Lippincott, 1991, p.
1765.
• Transverse most common

14. Obvious Fractures
Transverse fractures commonly result in The A/P view often makes visualization
wide fragment separation due to strong difficult, but should still be reviewed
ligamentous traction

15. Patellar Fractures
Interrogate the cortical borders for any The sunrise view is the best way to isolate the
irregularities (blue arrow), circle the patella patella to evaluate for injury
like clockwork (red arrow)

16. Management
• Non-displaced
– Intact extensor function: knee
immobilizer, rest, ice, analgesia, encourage WBAT
– Diminished extensor function:
immobilize, rest, ice, analgesia, NWB status, Ortho
referral 3-5d for ORIF
• Displaced >3mm
– Knee immobilizer, NWB status, ice, analgesia, early
Ortho referral for ORIF
• Severely comminuted or open
– Admit for OR, empiric ABx if open

17. Sunrise View
• This is only indicated for patients in which you
suspect a vertical fracture
• If you have a patient with an obvious
transverse fracture, flexion of the knee could
cause further separation

18. Merchant’s View
Modified sunrise, requires the angle to be 30°
Trochlear groove
1. The more prominent condyle (blue arrow)
denotes the side being imaged (i.e. if it is
prominent on the left, it is the left femur)
2. A normal patella has a degree of tilt to it
(lower right image)
3. The upper right image demonstrates
patellar subluxation as it is rotated lateral
to the trochlear groove

19. Pathologic Vertical Fracture
The fracture line extends from the cortical margin, is incomplete

20. Patellar Zebra
Bipartite Patella
• Normal anatomic
variant, commonly
misinterpreted as vertical
fracture
• Note the clean borders and
lack of cortical margin
disruption
• Most often located
superolateral
• If in doubt, get other knee
(is bilateral in 50% of
cases)

21. Patellar Positioning
• Patella “alta” and
“baja” denote a high-
riding and low-riding
patella, respectively, a
nd can be identified
by using Blumensaat’s
Line
• This is a line drawn by
the oblique
hyperlucent shadow
of the distal femur
(see left)

22. Patellar Sleeve Fracture
• Unique to children
• M>F 3:1, peak age 12.7yrs
• Avulsion fracture of the
distal patellar pole
• MOI: Forceful quadriceps
contraction against a fixed
lower leg or high impact
jumping
• PE: Look for
hemarthrosis, decreased
ability to extend leg, local
pain and TTP
• Tx: Knee immobilizer and 1. Patella alta (relationship to Blumensaat’s line)
ortho f/u for ORIF 2. May see small fragments of avulsed bone (blue
Bates DG, Hresko MT, and Jaramillo D. Patellar sleeve fracture:
Demonstration with MR imaging. Radiology 1994;193:825-827. arrows), but this is not always present
Hunt D and Somashekar N. A review of sleeve fracture of the
patella in children. The Knee 2005;12:3-7.

23. Patellar Sleeve Fracture
• Hemarthrosis and
physical exam
findings are more
Patella alta predictive than
radiographic
evidence
Hemarthrosis
• There is a high
morbidity
associated with this
injury, so a low
index of suspicion
should be held
Avulsed fragment

24. Dislocations
Not very
subtle…

25. Patellar Dislocations
• Most common knee
injury in children
• MOI: Pivoting on a
planted leg
• Presentation: Patella
laterally located and
knee held in flexion
• Associated fracture:
Lateral femoral condyle
or medial patellar margin

26. Tibial • Tibia bears 85% of knee wt
Plateau
• Fxs to articular surface
The most (plateau) often have high
important area to morbidity if undiagnosed
thoroughly
interrogate!
• Common fx mechanisms…
Fxs are 2/2 direct – Direct valgus/varus force
impaction of (lateral/medial blow)
femoral condyles – Compressive force (fall)
onto tibia

28. Tibial Plateau Fractures: Classifications
Based on the Schatzker
scheme…
1. Lateral condylar split
2. Split-compression
3. Pure lateral
compression
4. Medial condylar split
5. Bicondylar split
6. Split with
metadiaphysial
extension

29. Difficult to See
• Most TPFs are minimally displaced, making
their visualization difficult
– In addition, they most commonly occur along an
oblique plane and are not parallel to the x-ray
beam in any view
– Moreover, the tibial plateau surface slopes
inferiorly from anterior to posterior, meaning the
cortical surface of the plateau is never parallel to
the x-ray beam

30. Subtleties of the Tibia
• The normal (blue
arrow) tibial
trabeculae are more
dense medially (this
is where most of the
weight cephalad is
bore)
• If the lateral plateau
is more radiopaque,
consider a
compression fracture

31. Hemarthrosis
• Sometimes, all you get is a history, physical, and some subtle radiology
findings and we are expected to make the diagnosis.
• Look to the suprapatellar bursa for signs of a lipohemarthrosis that would
indicate an underlying TPF (blue arrow)

32. Type I: Lateral Split
• Ensure knee
stability on physical
exam (especially
MCL/ACL)
• Tx:
– Undisplaced/displa
ced, stable knee:
Immobilize, NWB
status 6-8wks
– Displaced w/
condylar widening
or unstable exam:
Immobilize, NWB,
will need surgery

33. Type I
• Closely evaluate the
plateau for any
disruptions in the
cortical margin (blue
arrow)
• Note the increased
trabecular density
laterally as
compared to medial
(yellow circle)

34. Type II: Split-Compression
• Commonly associated
with…
– Fibular head fxs
– Ligamentous injury
(19%)
• LCL most commonly
• Depression of >4mm
is clinically significant Depression
• From the ED,
immobilize and NWB
status until ortho f/u Split
for surgery

35. Type II: Split-Compression
Note the fracture line (red arrow) and Loss of the cortical rim of the lateral
slightly depressed articular surface (blue fragment (red arrows) and a subtle
arrow) depression (blue arrow) give this away

36. Type III: Pure Compression
• No associated lateral wedge
fracture but apparent central
or peripheral depression
• More common in the elderly
(osteoporotic)
• Seldom causes instability
• Position of knee at time of
injury usually dictates
severity of compression
(flexed 5x worse than
extended)
• Most treated non-
operatively:
– Immobilize and strict
NWB for 8-12wks

37. Type III
Note the cortical
depression
(yellow arrows)
without wedge
component.
Note the
increased
trabecular
markings (blue
circle) drawing
your attention to
the region

38. Type III (Lateral)
Note the
cortical
findings on
the A/P and
the obvious
depression is
only visualized
on the lateral

39. Type IV: Medial Split
• Indicates a higher
force of injury than
types I-III
• Beware of
underlying vascular
and ligamentous
damage (consider
arteriography)
• Intercondylar
eminence prone to
fracture as well
Immobilize and NWB status w/ Ortho
referral to decide on need for OR

40. Type V: Bicondylar
• Occasionally, can have an “upside-down Y” appearance
• 50% have meniscal detachment, 33% have ACL
avulsions

41. Type VI: Metaphysis Extension
All that needs to be said about these is …”Ouch”
Bicondylar w/ metaphyseal extension

42. Suprapatellar Bursa
The suprapatellar bursa is bounded by the quadriceps
tendon anteriorly and should measure less than 5mm
<5mm

43. Effusions
• These are often the only clues to a more significant underlying injury
• Best seen on lateral radiographs in the suprapatellar bursa, posterior to
the quadriceps tendon

44. Lipohemarthrosis
Blood and fat do not mix, with the fat (radiolucent)
layering on top of the blood (radiodense)

45. Can Use Ultrasound if Unclear
Fat is hyperechoic (light) and blood is
hypoechoic (dark) on ultrasound

46. Segond Fracture
• Proximal lateral
tibial avulsion
fracture 2/2 a
rupture from the
lateral capsular
ligament
• Associated with
ACL (>75%) and
meniscal (67%)
injuries
• Immobilizer, NWB
status, ortho f/u

47. Segond Fracture
Occasionally, there
can be a “mirror”
Segond where the
same process occurs
to the
proximomedial
aspect and is
associated with MCL
and PCL injuries as
well as the medial
meniscus.
(shown is a typical
Segond, not mirror)