If you have difficulty referencing the
Salter-Harris classification of fractures through the 
physis, remember the mnemonic "ME".
     Hey you !!  Who ME?  Yeah, you, what kind of 
Salter-Harris fracture is that?  ME stands for 
Metaphysis and Epiphysis.  The SH-I fracture, we all 
know is through the physis without any involvement of 
the metaphysis or epiphysis.  The SH-II fracture is 
through the metaphysis (M) and the physis.  The SH-III
fracture is through the epiphysis (E) and the physis.  
The SH-IV fracture is a contiguous fracture through the 
epiphysis, the physis, and the metaphysis (ME).  The 
SH-V fracture is a crush injury of the physis.

See diagram of the SH classes:

     An SH-I fracture may be suspected on clinical 
grounds alone.  The fracture line may not be 
radiographically evident if the epiphysis is not displaced.  
Tenderness over the physis should lead you to suspect 
an occult SH-I fracture in the region of the tenderness 
even if the radiographs are normal.  This commonly 
occurs in a wrist injury where normal wrist radiographs 
may lead one to the pitfall of diagnosing a wrist sprain.  
If there is tenderness over the physis of the distal radius 
or ulna, a clinical diagnosis of an SH-I fracture of this 
area should be made.  An SH-I fracture is only visible 
radiographically if the physis is widened, distorted, or 
the epiphysis is displaced.
     Radiographic confirmation of clinical SH-I fractures 
may be made later during orthopedic follow-up by 
stress views or the presence of new bone formation 
along the physis approximately 7-10 days post-injury.                

See SH-I example 

     This radiograph shows a tiny fracture of the ulnar 
styloid.  The AP view is otherwise unremarkable.  The 
patient had point tenderness over the dorsum of the 
radial physis.  The lateral view shows a displaced radial 
epiphysis.  On careful inspection, you can see that the 
radial epiphysis is not centered over the metaphysis.  
The radial epiphysis is slightly displaced dorsally with 
respect to the metaphysis.  No fractures of the 
epiphysis or the metaphysis are visible.  Since the 
fracture is strictly through the physis, this is a 
Salter-Harris type I fracture.
     
     An SH-II fracture occurs through the physis and 
metaphysis (M).

See SH-II example 

     This radiograph shows a fracture of the distal ulna    
and radius.  The radius fracture extends from the     
metaphysis into the physis.  The physis appears to
be slightly widened consistent with SH-II.
     
     An SH-III fracture occurs through the physis and 
epiphysis (E).  Since this fracture often involves the 
articular surface, this injury is more prone to chronic 
disability if anatomic realignment is not achieved.

See SH-III example.

     This radiograph shows a fracture of the distal tibia 
over the articular surface into the epiphysis and physis.
     
     An SH-IV fracture is a contiguous fracture through 
the metaphysis, physis, and epiphysis.  This fracture
often involves the articular surface, making this a
high-risk injury for chronic disability as in SH-III 
injuries.

See SH-IV  example.

     This radiograph shows a fracture of the medial 
malleolus extending from the inferior articular surface of 
the tibial epiphysis through the physis and extending 
through the metaphysis. 
     
     An SH-V fracture is a crush injury of the physis.  
This may be radiographically visible as a narrowing of 
the growth plate lucency; however, it is most often not 
radiographically visible.

See SH-V example.

     This patient fell off a second story balcony onto
her feet.  The radiographs show several fractures within 
the body of the calcaneus.  A Salter-Harris type V injury 
of the distal tibia  was suspected because of the 
mechanism of injury.  However, this type of injury is 
rarely visible on initial radiographs.  The injury must be 
suspected clinically.  Subsequent growth arrest of this 
area confirms the presence of the Salter-Harris type V
injury.
     Comparison views of the non-affected extremity may 
assist in radiographically diagnosing a SH-V type injury 
at initial presentation.  Based on this comparison view, 
differences in the width of the growth plates may be 
evident.  A complete obliteration or diminished physeal 
distance of the affected extremity confirms the 
diagnosis of a SH-V injury.   However, even if there are 
no obvious differences on the comparison view, or if a 
comparison view is not obtained, or if both extremities 
are injured, the patient should be treated as a possible 
SH-V injury if the mechanism of injury suggests an axial 
compression along the long axis of the bone, and the 
patient exhibits tenderness along the physeal region.

References
     1.  Bachman D, Santora S.  Orthopedic Trauma.
In:  Fleisher GR, Ludwid S (eds).  Textbook of
Pediatric Emergency Medicine, third edition.
Baltimore, MD, Williams and Wilkins, 1993,
pp. 1237-1238.