Delayed union

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Sclerotic fracture end of the radius in a dog with nonunion following fracture repair[1]

Delayed union or nonunion are a bone disease characterized by prolonged or absent fracture healing.

The rate of nonunion fracture is reported to be 3.4% of the total bone fractures in dogs. Nonunion is defined as the cessation of all reparative processes of healing without bony union. These fractures show movement at the fracture site and will not heal without surgical intervention[2].

There are a number of causes:

  • Excessive fracture movement, instability[3]
  • Osteomyelitis
  • Systemic disease resulting in delayed osteoclastic activity - e.g bacteremia, neoplasia, chronic fever
  • Hypocalcemia

Clinically affected dogs usually present with chronic lameness associated with orthopedic repair of a fracture. Joint stiffness, lethargy, regional swelling and fever may be apparent with secondary osteomyelitis.

Diagnosis is usually based on clinical evidence of poor fracture healing and definitive confirmation is usually obtained on radiographic analysis of fracture site[4].

Treatment usually requires improving fracture stability, and removing underlying metabolic or inflammatory disease.

Nonunion fractures often require the addition of cancellous bone autograft at the fracture site to stabilize the bone fracture.

Use of external fixators may be required in serious cases[5], or the exotic use of bone transport osteogenesis following resection of the nonunion segment of bone[6].


  1. Lee, HB et al (2009) Augmentation of bone healing of nonunion fracture using stem cell based tissue engineering in a dog: a case report. Veterinarni Medicina 54(4):198–203
  2. Millis DL & Jackson AM (2003) Delayed union, nonunion, and malunions. . In: Slatter D. (ed.): Textbook of Small Animal Surgery. 3rd ed. W.R, Saunders, Philadelphia. pp:1849–1861
  3. Perren SM (1979) Physical and biological aspects of fracture healing with special reference to internal fixation. Clin Orthop Rel Res 138:175
  4. Heppenstall RB (1980) Fracture Treatment and Healing. Philadelphia, WB Saunders
  5. Yardimci C et al (2011) Management of femoral fractures in dogs with unilateral semicircular external skeletal fixators. Vet Surg 40(3):379-387
  6. Ting D et al (2010) Bone transport osteogenesis for treatment of canine osteomyelitis. A report of two cases. Vet Comp Orthop Traumatol 23(2):134-140