This is a 16 year old male with a chief complaint of 
right knee pain.  He was jumping off a bench when he 
struck his knee on a nearby shopping cart twisting it as 
he fell onto the concrete surface.  He noted swelling of 
his knee and he was unable to bear weight on that side.  
He denies pain within the patella.
     His past medical history is unremarkable.
     Exam:  VS T36.7 (oral), P70, R18, BP 115/70.  He 
is healthy appearing and comfortable.  He has no areas 
of tenderness except for his right knee which is visibly 
swollen.  There are no abrasions, lacerations or visible 
bruises.  Swelling can be palpated beneath (posterior 
to) the patella.  The patella itself is not tender.  There is 
limited and painful range of motion.  The drawer sign is 
negative and his lateral stability appears to be good.  
The femoral condyles and the proximal tibia are 
non-tender.  His mid femur and hip are non-tender.  
Function, sensation, pulses and perfusion are all intact 
distally.
     He is told that he has a traumatic knee effusion 
probably due to a soft tissue injury.  Radiographs of his 
knee are ordered to rule out a fracture.  What is the 
likelihood that he has a fracture?

View knee radiographs:  AP, Lateral, Oblique
View AP view.


View lateral view.


View oblique view.


     AP, lateral, and oblique views of the knee are 
obtained.  There is a non-displaced intercondylar 
fracture of the distal femur extending vertically.  The 
fracture is only appreciated on the AP view.  These 
radiographs demonstrate that it may be very difficult to 
see some fractures at the wrong angle.  If a fracture is 
suspected, but not demonstrated on radiographs, 
consider obtaining other views to more definitively 
identify it.
     An orthopedic surgeon was consulted by phone.  He 
was placed in a long leg splint and orthopedic follow-up 
the next day was arranged.

Discussion
     Fractures of the knee may be very obvious 
clinically, but some of them are not.  Most radiographs 
of the knee will be normal, but it may be difficult to 
identify small fractures of the knee with only two views.
     Fractures of the distal femur are uncommon injuries.  
These can be classified as supracondylar, condylar, 
intercondylar and physeal.   Most of these fractures are 
large and are easily visible on AP and lateral 
radiographs.  In our patient's case, the intercondylar 
fracture is small.  Such intercondylar fractures often 
extend further superiorly forming a "T" or "Y" shape as 
they extend into the metaphysis of the distal femur.
     Distal femur fractures are usually due to fairly 
severe trauma.  They may be associated with ipsilateral 
hip fracture or dislocation, vascular injury, peroneal 
nerve injury or damage to the quadriceps insertions.

References:
     The Distal Femur (Chapter 17).  In:  Simon RR, 
Koenigsknecht SJ.  Emergency Orthopedics:  The 
Extremities, third edition.  1995, Norwalk, CT, 
Appleton & Lange, pp.  267-272.