Chapter 20.2 Nonunion Flashcards
What is a nonunion?
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.
How are nonunions classified?
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.
What causes most nonunions?
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.
What local factor is most commonly associated with nonunions?
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.
What is a common local factor for nonunions in miniature or toy breed dogs?
Limited vascular supply to the distal radius.
Fractures of this bone in these breeds have a marked propensity for becoming nonviable unions.
What is the main tissue present in biologically viable nonunions?
Unmineralized fibrocartilage.
This tissue is found in the zone between the fracture ends.
What are the classifications of biologically viable nonunions?
Hypertrophic
Slightly hypertrophic
Oligotrophic
Classification depends on the amount of callus present.
What characterizes hypertrophic nonunions?
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’.
What are slightly hypertrophic nonunions characterized by?
The same features as hypertrophic ones but with a smaller periosteal reaction.
This condition is usually referred to as a ‘horse hoof’.
What defines oligotrophic nonunions?
No radiographic signs of callus but still capable of biological activity.
The fracture ends are usually rounded and undergo decalcification.
What are the classifications of nonviable nonunions?
- Dystrophic
- Necrotic
- Defect
- Atrophic.
Each type has distinct characteristics related to callus formation and bone integrity.
What occurs in dystrophic nonunions?
A poorly vascularized intermediate fragment develops callus formation at one fracture end, but not at the other.
What happens in necrotic nonunions?
Major fragments of a comminuted fracture undergo devascularization and become necrotic, making callus formation impossible.
What characterizes defect nonunions?
A large bone defect where original bone tissue might have been lost during trauma, surgeries, or due to necrosis and resorption.
What are atrophic nonunions characterized by?
A defect at the fracture site with resorption of the adjacent bone ends.
How can nonunions be simplified for classification?
- 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.
What is a common clinical sign of nonunion in animals?
Lameness on the affected limb, which may be non-weight bearing
Muscle atrophy and joint stiffness may also be evident.
How does pain in nonunion cases compare to delayed unions?
Nonunions is less painful compared to delayed unions
Movement of the fracture may be present, but instability might not be clinically obvious.
What additional complication may be associated with nonunion?
Infection
Infection is generally associated with greater discomfort.
What radiographic features are indicative of nonunion?
- 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.
What does bone scintigraphy help differentiate in nonunions?
Viable and nonviable nonunions
This is particularly useful when there is no radiographic evidence of callus.
What is the definition of nonunion?
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.
What may be revealed by radiography in cases of implant-related nonunion?
Particularly instability reflected by lysis and implant loosening
This can help in understanding the failure of healing.
What is a potential consequence of disuse in the context of nonunion?
Osteopenia of neighboring bones
This can occur due to lack of movement and weight-bearing activities.
What is necessary to create an environment conducive to healing in nonunion treatment?
Surgical intervention
Surgical intervention is crucial for facilitating the healing process in cases of nonunion.
What must be assessed to determine the method of osteosynthesis in nonunion treatment?
The cause of the nonunion
Causes may include biological problems, mechanical reasons, or infections.
What should be performed to check for metabolic diseases before treatment?
A complete blood analysis
Addressing any metabolic or dietary problems is essential prior to treatment.
What type of examination provides information necessary for deciding on management of a fracture?
Serial radiographic examination
Radiographs help assess the fracture area for better treatment planning.
What should owners have regarding potential complications and outcomes of revision surgery?
Realistic expectations
Owners should be informed about the risks and likelihood of success.
What is the usual aim regarding hardware at the site of a nonunion?
To remove all hardware
It is rare to find functional implants in nonunion cases.
What must be done to ischemic bone fragments in nonunion treatment?
They must be removed
Avascular tissue, including soft tissue, should also be excised.
What is the theoretical approach to active nonunions regarding debridement?
It is unnecessary to debride
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.
What is indicated if bacterial contamination or infection is suspected?
Copious lavage
This procedure helps cleanse the area of potential infection.
What should be considered if fibrosis is too advanced during surgery?
Muscle resection
Advanced fibrosis may require removing affected muscle tissue.
What is mandatory in biologically inactive non-unions?
Bone grafts
Bone grafts are essential for promoting healing in inactive non-unions.
What is the preferred donor site for autogenous cancellous bone grafting?
Proximal humerus
This site is chosen due to its accessibility and reduced postoperative morbidity.
What is a recent commercial product used in bone healing, though expensive?
Recombinant human bone morphogenetic protein (rhBMP-2)
Its high cost limits widespread use despite its potential benefits.
What type of fixation is essential for successful nonunion treatment?
Rigid fixation
Dynamic compression plate stabilization is commonly preferred.
What do both linear and circular external skeletal fixators allow?
Limited postoperative adjustments
These fixators also help avoid infection by being placed away from the wound site.
What should be placed if there is fluid accumulation around the revised fracture?
Closed suction drains
These drains help prevent deleterious effects on healing.
How long may antibiotic therapy be required where infection is established in a fracture site?
6–8 weeks
Duration of therapy depends on the severity of the infection.
What is the aim of all revision surgery in nonunion cases?
A rapid return to normal function
This includes aggressive physical therapy and controlled weight-bearing exercises.
What is a common exception regarding the prognosis for bone healing?
Atrophic nonunion of the distal radius in toy breed dogs
This specific case often has a poor healing prognosis.
What is the general treatment approach for nonunion?
Removing loose implants, stabilizing the fracture, and adding cancellous bone autograft as needed
This comprehensive approach addresses various aspects of nonunion treatment.
What must be done to the sclerotic or atrophic bone ends of biologically inactive nonunions?
They must be osteotomized to expose their medullary cavities and improve vascularity.
This process is necessary to enhance healing potential in nonunion cases.
What is an alternative to osteotomy for sclerotic bone ends?
Multiple holes can be drilled through their sclerotic ends.
Drilling helps in improving vascularity but may not be as effective as osteotomy.
What is the purpose of osteotomy in the treatment of nonunions?
To facilitate apposition of the bone fragments.
Apposition is crucial for proper healing and alignment of bone fragments.
What is a consequence of performing an osteotomy?
It will inevitably result in limb shortening.
This is an important consideration when planning surgical intervention for nonunions.
