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The bone involved and the location within the bone should be described as per Table 3.2. Fractures distal to the carpus/tarsus have a more favourable prognosis, primarily due to the capacity to supplement internal fixation with external coaptation [172], but are still associated with challenges including poor soft tissue coverage [173].

Physeal fractures generally occur in foals and yearlings, and may be classified according to the Salter–Harris type I–V scheme [174–176] (Figure 3.20). Physeal fractures are typically caused by a combination of compressive, shear and bending forces [176]. The proximal ulnar physis is not involved in the formation of a joint and is therefore termed an apophysis. The Salter–Harris classification system is therefore not completely applicable to fractures of the proximal ulnar physis, and a specific type 1–5 scheme is applied [178].

Table 3.1 Predictable sites of stress fractures and stress remodelling.

Bone/joint	Anatomical region	References
Scapula	Distal aspect of the spine	[140] [145]
Humerus	Caudoproximal Craniodistal Medial diaphyseal Caudodistal	[146] [144, 147] [148, 149]
Carpus	Dorsomedial third carpal bone Radial carpal bone Intermediate carpal bone	[150] [151] [89]
Third metacarpal	Mid‐diaphyseal and supracondylar Parasagittal groove Proximal palmar Dorsal cortex Distal condyle	[152] [60] [153] [154] [69] [155]
Proximal sesamoid	Palmar flexor region Medial sesamoid abaxial mid‐body subchondral bone	[38] [156]
Proximal phalanx	Sagittal groove	[157] [158]
Pelvis	Ilial wing Pubis	[159] [137] [160] [161] [162]
Tibia	Distomedial Caudoproximal Caudal diaphyseal Proximolateral under the head of the fibula	[163] [164] [148]
Tarsus	Dorsolateral third tarsal bone	[165] [166]
Lumbar spine	L5–L6 vertebral junction	[136]

The most common physeal fracture in horses is a Salter–Harris type II [175]. These have been reported in the third metacarpal and metatarsal distal physes, distal femoral physis and proximal tibial physis [175–177]. Physeal fractures of the proximal tibia have a typical pattern of type II with a lateral metaphyseal corner [179]. Type IV injuries tend to be unstable and many require internal fixation [180]. Bridging of the physis during internal fixation of physeal fractures should be avoided if possible as it may result in premature closure and subsequent development of angular limb deformity [180]. Type V injuries are rare, and are often not initially radiographically detectable, but manifest as a progressive angular limb deformity [176].

Table 3.2 Features and qualifiers of features applicable to fracture description.

Source: Stover [170]. Reproduced with permission of Sage Publication.

Feature	Qualifier	Description
Location	Epiphysis	Fracture involves the end of a long bone
Physis	Fracture involves an open physisa
Metaphysis	Fracture involves a region of the bone adjacent to the physis on the side closest to the diaphysis
Diaphysis	Fracture involves the central region of a long bone
Direction	For example, proximodorsal to distopalmar	Direction(s) of the fracture line(s) is (are) described from proximal to distal unless the direction of propagation is known (e.g. MCIII/MTIII condylar fractures progress from distal to proximal)
Plane	For example, transverse, oblique, longitudinal, sagittal and dorsal	Orientation of the predominant fracture line
Configuration	Transverse	Fracture courses perpendicular to the longitudinal axis of the bone
Longitudinal	Fracture courses parallel to the longitudinal axis of the bone
Oblique	Fracture courses along a flat plane obliquely through the bone (i.e. not parallel to a transverse or longitudinal plane)
Spiral	Fracture has a spiral component
Butterfly	Fracture has transverse and oblique components
Extent	Complete	Fracture courses completely through the bone, dividing it into two or more separate fragments
Incomplete	Fracture does not course completely through the bone
Displacement	Nondisplaced	Fracture fragments remain in anatomic apposition
Displaced	Fracture fragments separated, angulated or overriding, and no longer in anatomic apposition
Complexity	Simple	One fracture line dividing the bone into two separate fragmentsb
Intermediate	May have one or two sizeable bony fragments (e.g. complete mid‐diaphyseal metacarpal/metatarsal fracture with a butterfly component)
Complex	Multiple fracture lines and ≥3 bony fragments or greater comminution
Joint involvement	Non‐articular	The fracture does not extend through an articular surface
Articular	The fracture courses through an articular surface
Contamination	Closed	The skin overlying the fractured bone is intact and not penetrated by the injury
Open	The skin has a wound over the fracture that introduces contamination and increases the risk of infectionc
Other	Avulsion	A fracture fragment that distracted from the parent bone by tension through a soft tissue (tendon and ligament) attachment
Slab	A biarticular fracture with the fracture plane perpendicular to the articular surfaces of the parent bone
Condylar	Fracture involves a condyle

^a Physeal fractures are further described according to the Salter–Harris classification scheme.

^b One or two minor bone chips do not change the definition of a fracture as simple.

^c Open fractures are further classified according to [171].