First and second year — the floor first, then every step
Name the Salter–Harris type by what the fracture line crosses — physis, metaphysis, epiphysis — because the type predicts growth disturbance; compare the physeal width with the other side when the film looks normal.
Orient first
The physis is weaker than the ligaments in a child, so a mechanism that sprains an adult's ligament fractures a child's growth plate.
A Salter–Harris I fracture can be radiographically invisible except for physeal widening or soft-tissue swelling over the physis.
Fractures that cross the germinal layer (types III and IV) and crush injuries (type V) threaten growth; physeal bars form months later.
Acquire the study
Two orthogonal views; a comparison view of the other side when physeal widening is the question.
The manoeuvre
Trace the physis on both views: widening or irregularity compared with the other side at the same site.
Follow the fracture line on both views: through the physis only (I), exiting through the metaphysis (II — the Thurston–Holland fragment), through the epiphysis to the articular surface (III), across metaphysis, physis and epiphysis (IV).
Lateral view: joint effusion, and soft-tissue swelling centred on the physis compared with the contralateral side.
What confirms it
A fracture line related to the physis, or physeal widening against the other side with local tenderness.
What licenses you to exclude it
A normal radiograph does not exclude a Salter–Harris I fracture; with physeal tenderness it is treated as one.
The classic misread
Calling a normal-for-age physis widened without a comparison.
Reporting the injury
Classification to use
Salter–Harris I–V (I physis only; II physis + metaphysis; III physis + epiphysis; IV metaphysis + physis + epiphysis; V crush). Adolescent ankle: juvenile Tillaux and triplane fractures described separately.
Measurements — and how to take them
Epiphyseal displacement in mm; articular gap and step-off in mm for III/IV and triplane/Tillaux (≥ 2 mm is a commonly used operative threshold — verify).
Physeal bar: its area as a percentage of the physis on MRI.
What to report
Bone, physis, Salter–Harris type, displacement, articular step-off (III/IV), and on follow-up any physeal bar with its size and location.
How to report it
X-ray: "Salter–Harris II fracture of the distal radius with a dorsal metaphyseal fragment and 4 mm dorsal displacement of the epiphysis."
CT: "Triplane fracture of the distal tibia with 3 mm articular gap at the plafond."
What not to report
Do not diagnose physeal widening without the comparison view or a stated normal range for the age.
Associated injuries to look for
Non-accidental injury in infants and young children, especially with metaphyseal corner fractures; neurovascular injury at the distal femur and elbow.
What changes management
Displaced III/IV fractures and articular step-off — anatomical reduction and fixation.
A physeal bar — resection or epiphysiodesis depending on its size and the remaining growth.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Physis · Physeal width
thin and uniform, symmetrical with the contralateral side
Standard AP radiograph of the joint, compared side to side.
Widening and metaphyseal fraying suggest rickets or a chronic stress injury (as in the gymnast wrist); focal widening suggests a Salter–Harris I injury. ⚠️ The contralateral side is the reference — physeal appearance varies with age and site, and no single absolute width applies.
I = through the physis. II = physis + metaphysis (Thurston-Holland fragment). III = physis + epiphysis. IV = metaphysis + physis + epiphysis. V = crush of the physis. Extended / Rang types exist for perichondral injury. Type is the report, not a millimetre of displacement alone
A type I can be occult on a radiograph (the physeal-width entry is the clue). The contralateral side is the reference.
X-ray
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.