Chapter 20.2 Nonunion

Question 1

What is a nonunion?

Answer 1

A fracture that has failed to heal and does not show any further signs of progression towards consolidation.

Each nonunion is, in its early stage, a delayed union.

Question 2

How are nonunions classified?

Answer 2

As viable (biologically active) or nonviable (biologically inactive).

Biologically active nonunions have a variable amount of callus that fails to bridge the fracture gap, while nonviable nonunions have no such callus.

Question 3

What causes most nonunions?

Answer 3

Poor decision making and technical failure on the part of the surgeon.

It is not typically a failure attributed to the animal or its owner.

Question 4

What local factor is most commonly associated with nonunions?

Answer 4

A fracture gap that exceeds the regenerative capacity of the bone.

Soft-tissue trauma and the transient extraosseous blood supply are also significant local factors.

Question 5

What is a common local factor for nonunions in miniature or toy breed dogs?

Answer 5

Limited vascular supply to the distal radius.

Fractures of this bone in these breeds have a marked propensity for becoming nonviable unions.

Question 6

What is the main tissue present in biologically viable nonunions?

Answer 6

Unmineralized fibrocartilage.

This tissue is found in the zone between the fracture ends.

Question 7

What are the classifications of biologically viable nonunions?

Answer 7

Hypertrophic
Slightly hypertrophic
Oligotrophic

Classification depends on the amount of callus present.

Question 8

What characterizes hypertrophic nonunions?

Answer 8

Well marked signs of healing but the process has ceased, with enlarged bone ends due to bone apposition.

This nonunion is usually referred to as an ‘elephant foot’.

Question 9

What are slightly hypertrophic nonunions characterized by?

Answer 9

The same features as hypertrophic ones but with a smaller periosteal reaction.

This condition is usually referred to as a ‘horse hoof’.

Question 10

What defines oligotrophic nonunions?

Answer 10

No radiographic signs of callus but still capable of biological activity.

The fracture ends are usually rounded and undergo decalcification.

Question 11

What are the classifications of nonviable nonunions?

Answer 11

• Dystrophic
• Necrotic
• Defect
• Atrophic.

Each type has distinct characteristics related to callus formation and bone integrity.

Question 12

What occurs in dystrophic nonunions?

Answer 12

A poorly vascularized intermediate fragment develops callus formation at one fracture end, but not at the other.

Question 13

What happens in necrotic nonunions?

Answer 13

Major fragments of a comminuted fracture undergo devascularization and become necrotic, making callus formation impossible.

Question 14

What characterizes defect nonunions?

Answer 14

A large bone defect where original bone tissue might have been lost during trauma, surgeries, or due to necrosis and resorption.

Question 15

What are atrophic nonunions characterized by?

Answer 15

A defect at the fracture site with resorption of the adjacent bone ends.

Question 16

How can nonunions be simplified for classification?

Answer 16

• Callus formation (hypertrophic and moderately hypertrophic viable nonunions)
• No callus formation (viable oligotrophic and non-viable nonunions).

The distinction between the latter types is somewhat academic, and their treatment is identical.

Question 17

What is a common clinical sign of nonunion in animals?

Answer 17

Lameness on the affected limb, which may be non-weight bearing

Muscle atrophy and joint stiffness may also be evident.

Question 18

How does pain in nonunion cases compare to delayed unions?

Answer 18

Nonunions is less painful compared to delayed unions

Movement of the fracture may be present, but instability might not be clinically obvious.

Question 19

What additional complication may be associated with nonunion?

Answer 19

Infection

Infection is generally associated with greater discomfort.

Question 20

What radiographic features are indicative of nonunion?

Answer 20

• Persistent gap at the fracture plane
• Rounded, well-defined or sclerotic fracture ends
• Obliteration of the medullary cavity by endosteal callus
• Displacement of the bone ends

Sequestra may also be evident.

Question 21

What does bone scintigraphy help differentiate in nonunions?

Answer 21

Viable and nonviable nonunions

This is particularly useful when there is no radiographic evidence of callus.

Question 22

What is the definition of nonunion?

Answer 22

Nonunion is diagnosed when there is no evidence of fracture healing over several months

Radiographically, this is characterized by specific features and may indicate underlying issues.

Question 23

What may be revealed by radiography in cases of implant-related nonunion?

Answer 23

Particularly instability reflected by lysis and implant loosening

This can help in understanding the failure of healing.

Question 24

What is a potential consequence of disuse in the context of nonunion?

Answer 24

Osteopenia of neighboring bones

This can occur due to lack of movement and weight-bearing activities.

Question 25

What is necessary to create an environment conducive to healing in nonunion treatment?

Answer 25

Surgical intervention ## Footnote Surgical intervention is crucial for facilitating the healing process in cases of nonunion.

Question 26

What must be assessed to determine the method of osteosynthesis in nonunion treatment?

Answer 26

The cause of the nonunion ## Footnote Causes may include biological problems, mechanical reasons, or infections.

Question 27

What should be performed to check for metabolic diseases before treatment?

Answer 27

A complete blood analysis ## Footnote Addressing any metabolic or dietary problems is essential prior to treatment.

Question 28

What type of examination provides information necessary for deciding on management of a fracture?

Answer 28

Serial radiographic examination ## Footnote Radiographs help assess the fracture area for better treatment planning.

Question 29

What should owners have regarding potential complications and outcomes of revision surgery?

Answer 29

Realistic expectations ## Footnote Owners should be informed about the risks and likelihood of success.

Question 30

What is the usual aim regarding hardware at the site of a nonunion?

Answer 30

To remove all hardware ## Footnote It is rare to find functional implants in nonunion cases.

Question 31

What must be done to ischemic bone fragments in nonunion treatment?

Answer 31

They must be removed ## Footnote Avascular tissue, including soft tissue, should also be excised.

Question 32

What is the theoretical approach to active nonunions regarding debridement?

Answer 32

It is unnecessary to debride ## Footnote Compression should create the biomechanical environment necessary for healing. Whenever doubt exists, it is better to debride any dubious tissue and pack the defect with autogenous cancellous bone. On occasions, removal of some of the exuberant callus may make contouring of a compression plate over the fracture site easier.

Question 33

What is indicated if bacterial contamination or infection is suspected?

Answer 33

Copious lavage ## Footnote This procedure helps cleanse the area of potential infection.

Question 34

What should be considered if fibrosis is too advanced during surgery?

Answer 34

Muscle resection ## Footnote Advanced fibrosis may require removing affected muscle tissue.

Question 35

What is mandatory in biologically inactive non-unions?

Answer 35

Bone grafts ## Footnote Bone grafts are essential for promoting healing in inactive non-unions.

Question 36

What is the preferred donor site for autogenous cancellous bone grafting?

Answer 36

Proximal humerus ## Footnote This site is chosen due to its accessibility and reduced postoperative morbidity.

Question 37

What is a recent commercial product used in bone healing, though expensive?

Answer 37

Recombinant human bone morphogenetic protein (rhBMP-2) ## Footnote Its high cost limits widespread use despite its potential benefits.

Question 38

What type of fixation is essential for successful nonunion treatment?

Answer 38

Rigid fixation ## Footnote Dynamic compression plate stabilization is commonly preferred.

Question 39

What do both linear and circular external skeletal fixators allow?

Answer 39

Limited postoperative adjustments ## Footnote These fixators also help avoid infection by being placed away from the wound site.

Question 40

What should be placed if there is fluid accumulation around the revised fracture?

Answer 40

Closed suction drains ## Footnote These drains help prevent deleterious effects on healing.

Question 41

How long may antibiotic therapy be required where infection is established in a fracture site?

Answer 41

6–8 weeks ## Footnote Duration of therapy depends on the severity of the infection.

Question 42

What is the aim of all revision surgery in nonunion cases?

Answer 42

A rapid return to normal function ## Footnote This includes aggressive physical therapy and controlled weight-bearing exercises.

Question 43

What is a common exception regarding the prognosis for bone healing?

Answer 43

Atrophic nonunion of the distal radius in toy breed dogs ## Footnote This specific case often has a poor healing prognosis.

Question 44

What is the general treatment approach for nonunion?

Answer 44

Removing loose implants, stabilizing the fracture, and adding cancellous bone autograft as needed ## Footnote This comprehensive approach addresses various aspects of nonunion treatment.

Question 45

What must be done to the sclerotic or atrophic bone ends of biologically inactive nonunions?

Answer 45

They must be osteotomized to expose their medullary cavities and improve vascularity. ## Footnote This process is necessary to enhance healing potential in nonunion cases.

Question 46

What is an alternative to osteotomy for sclerotic bone ends?

Answer 46

Multiple holes can be drilled through their sclerotic ends. ## Footnote Drilling helps in improving vascularity but may not be as effective as osteotomy.

Question 47

What is the purpose of osteotomy in the treatment of nonunions?

Answer 47

To facilitate apposition of the bone fragments. ## Footnote Apposition is crucial for proper healing and alignment of bone fragments.

Question 48

What is a consequence of performing an osteotomy?

Answer 48

It will inevitably result in limb shortening. ## Footnote This is an important consideration when planning surgical intervention for nonunions.