Felis ISSN 2398-2950

Fracture: overview

Contributor(s): James Cook, Susan Rackard, J Yovich, Richard Meeson

Introduction

  • Cause: fractures are caused when the force applied to the bone exceeds the ultimate strength of the bone. 
  • The type of fracture depends on the size and direction of the force applied to it and the shape, size and structure of the bone involved.
  • Separation of the fracture fragments and, therefore, the degree of instability, depends on the severity of the fracture and tension forces from surrounding tissues and attachments.
  • Types: fractures can be separated into 6 broad groups:
    • Oblique.
    • Transverse.
    • Comminuted.
    • Spiral.
    • Segmental.
    • Epiphyseal.
  • Fractures may be:
    • Either Open - skin wound communicating with fracture site.
    • Or Closed - overlying skin is intact.
  • Signs: vary according to site, type, degree of instability, severity of fracture, whether 'open' or 'closed'.
  • Treatment: conservative management, external coaptation Fracture fixation: casts, external  Fracture: external fixation or internal fixation Fracture: internal fixation  - depends on site, type, severity of fracture.
  • Prognosis: dependent upon site, type, severity, method of repair, age, concurrent injuries or pathology.

Pathogenesis

Etiology

  • Direct trauma, eg HBC (RTA) (most common), gun shot, air gun pellet.
  • Compression, eg fall from height.
  • Bending or shearing forces, eg trapped limb.

Predisposing factors

General

Specific

Epiphyseal

  • Open growth plate (skeletally immature animal) Epiphyseal trauma and older male neutered cats.

Pathophysiology

  • Fractures are caused when the force applied to the bone exceeds the ultimate strength of the bone.
  • See also fracture healing Fracture: healing.
  • Fractures can be separated into 6 broad groups:
    • Incomplete - greenstick.
    • Oblique.
    • Transverse.
    • Comminuted.
    • Spiral.
    • Segmental.
    • Associated with growth plate (physis) (Salter-Harris classification) .
  • Fractures may be:
    Either Open (compound) - skin wound communicating with fracture site - Grades I, II, III.
    Or Closed (simple) - overlying skin is intact.
  • Fractures may be:
    Either Complete - total disruption of bone continuity.
    Or Incomplete - 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.

 Force

  • Torsion  →  spiral fractures.
  • Shearing/tension/bending  →  transverse fractures.
  • Compression/bending  →  oblique fractures with/without comminution.
  • High energy stress, eg HBC (RTA) or gun shot 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

  • The resistance of a particular bone to external forces is dependent upon the composition of that bone, ie the proportions of cortical:cancellous bone:
    • Cortical bone - strong against compression; weak against shearing perpendicular to long axis.
    • Cancellous (trabecular) bone - strong against compression; weak against tension.
  • Long bones have a wide metaphysis of cancellous bone - suited to absorb large amounts of compression energy.

Bone shape and size

  • Cylindrical shape resists torsion, eg long bones.
  • Square shape (rounded angles) resists bending, eg majority of bones.
  • Cross sectional area, length and the shape of the bone as it relates to the neutral axis, however most cats are fairly similar in size.

Site

  • 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 HBC (RTA) and risk of comminution and beiong open.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Nolte D M, Fusco J V & Peterson M E (2005) Incidence of and predisposing factors for nonunion of fractures involving the appendicular skeleton in cats: 18 cases (1998-2002). JAVMA 226 (1), 77-82 PubMed.
  • Scott H (2005) Repair of long bone fractures in cats. In Practice 27 (8), 390-397 VetMedResource.
  • Harari J (2002) Treatments for feline long bone fractures. Vet Clin North Am Small Anim Pract 32 (4), 927-947 PubMed.

Other sources of information

  • Tobias K & Johnston S  (2011) Veterinary Surgery: Small Animal. 1st edn. W B Saunder & Co. pp 565-571, 647-656.
  • Montavon P M, Voss K & Langley-Hobbs S J (eds) (2009) Feline Orthopedic Surgery and Musculoskeletal Disease. Saunders ISBN: 978-0-7020-2986-8. 


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