Canis ISSN: 2398-2942

Fracture: overview

Contributor(s): Susan Rackard, Prof Walter Renberg, Richard Meeson


  • Fractures occur when the forces acting on a bone exceed its ultimate strength.
  • The type of fracture occurring is dependent on the magnitude, rate and direction of the force applied to it, and also the shape, size and structure of the bone involved.
  • Separation of the fracture fragments, and therefore the degree of instability, is dependent on the severity of the fracture and any restraining forces from surrounding tissues and their attachments.
  • Signs: vary according to site, type, degree of instability, severity of fracture, whether 'open' or 'closed'.
  • Treatment: coaptation, external or internal fixation may be necessary - dependent upon site, type, severity of fracture Fracture: internal fixation Fracture: external fixation.
  • Prognosis: dependent upon site, type, severity, method of repair,age and co-morbidities.



  • Direct trauma, eg road traffic accident (most common), gun shot.
  • Compression, eg fall from height.
  • Shearing forces, eg trapped limb.

Predisposing factors





  • Fractures are caused when the force applied the bone exceeds the ultimate strength of the bone.
  • Fractures can be separated into 6 broad groups:
    • Oblique.
    • Transverse.
    • Comminuted.
    • Spiral.
    • Segmental.
    • Associated with the growth place (physis) (Salter-Harris classification ).
  • Fractures may be:

    Either Open - skin wound communicating with fracture site.

    Or Closed - overlying skin is intact.

  • Fractures may be:
    Either Complete (most common) - total disruption of bone continuity.
    Or Incomplete (rare) - partial continuity of bone maintained, eg Greenstick fracture (young animals), fissure fracture (adults).
  • Relative displacement of fracture fragments:
    • Distraction/avulsion - pull of tendon/ligament/muscle attachments separate bone fragments.
    • Compression - compressive force shortens bone, eg vertebra.
    • Depression - concave deformity of bone, eg skull, from applied force.
    • Impaction - fractured bone ends driven into one another.
  • Type depends upon:
  • Size and direction of the force applied.
  • Bone structure.
  • Bone shape.
  • Site.


  • Torsion → spiral fractures.
  • Shearing/tension/bending → transverse fractures.
  • Compression/bending → oblique fractures with/without comminution.
  • High energy stress, eg RTA or ballistic often → severe comminution and damage to surrounding tissue.
  • A combination of the above forces are usually acting in any one instance → variable fracture patterns.

Bone structure and shape

  • Both the bone structure and shape affect the manner in which a fracture occurs.
  • Cross-sectional area, length and the shape of the bone as it relates to the neutral axis. As such, a bigger dog's femur will fail at a higher load than a smaller dog's femur.


  • The type of stresses acting on a bone will vary according to the site of the bone, eg:
    • Vertebrae/Long bone metaphyses - compression.
    • Patella/Traction epiphyses - tension.
    • Humeral condyle - shearing.
    • Long bone diaphyses - bending.
    • Tibia/humerus - torsion.
  • Exposure/degree of protection by surrounding tissue affects fracture incidence/type, eg distal limbs have little covering tissue to absorb external forces → high incidence of limb fractures in general trauma, eg road traffic accident and risk of comminution and being open in nature.


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Further Reading


Refereed papers

Other sources of information

  • Tobias K & Johnston S  (2011) Veterinary Surgery: Small Animal. 1st edn. W B Saunder & Co. pp 565-571, 647-656.
  • Fossum T W (1997) Small Animal Surgery. St Louis: Mosby Year Book.
  • Piermattei D & Flo G (1997) Handbook of Small Animal Orthopaedics and Fracture Repair. 3rd ed. Philadelphia: W B Saunders & Co.