Chapter 20.1 Delayed Unions

Question 1

What is the difference between an excellent and a poor outcome in fracture repair often attributed to?

Answer 1

The difference is sometimes a matter of mere details.

Question 2

What is a delayed union?

Answer 2

A delayed union is a fracture that takes longer to heal than anticipated.

Question 3

What factors determine the rate and extent of fracture healing?

Answer 3

The biological and mechanical environments.

Question 4

What is essential for fracture healing?

Answer 4

Adequate vascularity of the bone and soft tissues.

Question 5

What usually causes inadequate vascular supply in fracture healing?

Answer 5

Soft-tissue trauma.

Question 6

What is a sequestrum?

Answer 6

A piece of dead bone surrounded by an involucrum.

An involucrum is a layer of new bone growth that forms around a sequestrum (a piece of dead bone) in response to infection, particularly in cases of chronic osteomyelitis.

Question 7

What happens if a bone is deprived of its vascular supply?

Answer 7

It may become a sequestrum.

Question 8

What can result from inadequate fracture fixation?

Answer 8

Development of a delayed union or even a nonunion.

Question 9

What can high interfragmentary strain prevent?

Answer 9

Progression from granulation tissue to fibrocartilage and eventually bone.

Question 10

What may cause implants to be unstable?

Answer 10

They may be undersized or have insufficient bone–implant contact.

Question 11

What type of pins should be used in a linear external fixator for long-term stability?

Answer 11

Threaded pins.

Question 12

How does stability differ from rigidity in fracture fixation?

Answer 12

Stability refers to the ability to maintain position, while rigidity refers to the inability to move.

Question 13

What factors can be classified as responsible for the development of a delayed union?

Answer 13

• Initial trauma
• Contamination
• Vascular insufficiency

Question 14

What happens to the vascular supply when kinetic energy from a traumatic insult is high?

Answer 14

The damage to the vascular supply increases, leading to a higher likelihood of necrosis and infection.

Question 15

What is a typical example of a high-kinetic energy injury?

Answer 15

A gunshot wound with high-speed pellets.

Question 16

What can occur if asepsis is not practiced in an open wound with devitalized tissues?

Answer 16

It is easily contaminated with highly resistant pathogens.

Question 17

Delayed unions may be caused by _______.

Answer 17

• vascular insufficiency
• fracture instability
• inadequately chosen or applied implants.

Question 18

What is the most important feature of the mechanical environment of a fracture?

Answer 18

Stability

Stability is crucial to prevent delayed union or nonunion.

Question 19

What type of tissue forms initially at a fracture site?

Answer 19

Granulation tissue

• Granulation Tissue tensile force up to 0.1 Nm/mm2.
• Early Soft Callus tensile force is 4–19 Nm/mm2
• Ultimate tensile strength of compact bone is 130 Nm/mm2

This may progress to fibrocartilage and eventually bone as strain decreases.

Question 20

What factors can lead to unstable implants?

Answer 20

• Undersized implants
• Insufficient bone–implant contact
• Inappropriate selection of fixation devices

Examples include too small plates or inadequate size pins.

Question 21

What is a potential issue with using a linear external fixator for a highly comminuted fracture?

Answer 21

Insufficient bone–implant contact

This occurs when only two pins are used for each fracture segment.

Question 22

What type of pins should be used for long-term stability with a linear external fixator?

Answer 22

Threaded pins

They are stronger and provide better bone purchase than smooth pins.

Question 23

Circular external fixator provides stability or rigidity?

Answer 23

The circular external fixator provides stability but not rigidity due to its tensioned cross wires.

Stability allows for micromotion, while rigidity does not

Question 24

What are the factors responsible for the development of a delayed union?

Answer 24

• Initial trauma
• Contamination at the site of the accident

These factors can lead to complications such as necrosis and infection.

Question 25

How does kinetic energy from trauma affect fracture healing?

Answer 25

Higher kinetic energy results in greater damage to vascular supply ## Footnote This increases the likelihood of necrosis and infection.

Question 26

What is a typical example of high kinetic energy trauma?

Answer 26

Gunshot wound with high-speed pellets ## Footnote This can cause cavitation and extensive tissue disruption.

Question 27

What is a risk associated with comminuted, highly unstable fractures during transportation?

Answer 27

Creation of avascular bone fragments ## Footnote Detached fragments may become sequestra due to loss of vascular supply.

Question 28

Which types of fractures are particularly prone to becoming open fractures?

Answer 28

Long oblique and spiral fractures ## Footnote Sharp points of their bone ends can penetrate the skin.

Question 29

Which metabolic conditions can delay fracture healing?

Answer 29

Primary hyperparathyroidism Hyperadrenocorticism Diabetes mellitus Hyper- and hypothyroidism Growth hormone deficiency Renal disease Hepatobiliary disease Intestinal malabsorption ## Footnote These conditions are important to consider in treatment.

Question 30

What nutritional deficiencies are associated with disturbed bone production?

Answer 30

* Calcium and phosphorus imbalance * Vitamin A and D deficiency * Vitamin K and copper deficiency ## Footnote These deficiencies can affect healing and bone health.

Question 31

Which drugs can interfere with bone healing?

Answer 31

* Corticosteroids * Anti-convulsants * Antineoplastic agents ## Footnote Awareness of these medications is crucial during treatment.

Question 32

Why is well-vascularized bone important in fracture healing?

Answer 32

It heals more rapidly and has greater resistance to infection ## Footnote Inadequate reconstruction can lead to complications.

Question 33

What is intraoperative skeletal traction ?

Answer 33

Intraoperative skeletal traction refers to the use of traction applied to bones during surgery, often to reduce fractures or correct deformities ## Footnote Helps preserve the osseous vascular supply. Fragment manipulation necessary for anatomical reduction

Question 34

What can jeopardize even well-performed surgeries?

Answer 34

An uncooperative owner allowing excessive exercise ## Footnote Proper postoperative management is crucial for recovery.

Question 35

How are delayed unions diagnosed?

Answer 35

Through serial clinical and radiographic evaluations ## Footnote These evaluations assess the progression of bone healing.

Question 36

What is the diagnosis of a delayed union based on?

Answer 36

A quantitative judgment based on the expected rate of healing ## Footnote Factors such as age, type of bone, and biomechanical environment are considered.

Question 37

What should be evaluated postoperative for boney healing?

Answer 37

Both clinical and radiographic evaluations ## Footnote Neither method alone provides definitive information.

Question 38

What *clinical signs* may suggest a delayed union?

Answer 38

Increased pain or decreased use of the limb ## Footnote Instability of the fracture is usually not evident unless related to implant issues.

Question 39

What should be expected within a few days after surgery regarding joint assessment?

Answer 39

The animal should tolerate assessment of range of motion of proximal and distal joints ## Footnote Articular fractures may require longer before movement can occur without pain.

Question 40

When should radiographic examinations be scheduled to assess fracture healing?

Answer 40

Immediately postoperative, after 7-10 days, after 25-30 days, and after 2 months ## Footnote Additional checks may be scheduled if healing is slower than expected.

Question 41

What can mask the appearance of an active callus on radiographs?

Answer 41

Incorrect exposure with too high a kV ## Footnote This can obscure delicate callus formation if imaging is done too early.

Question 42

What is the radiographic appearance of a delayed union compared to normal healing?

Answer 42

The same, but changes occur at different time points ## Footnote A persistent fracture line with some nonbridging callus is characteristic.

Question 43

What are the types of ossification involved in the healing process?

Answer 43

* Intramembranous ossification (surface of collagen fiber bundles) * Endochondral ossification (surface of fibrocartilaginous areas) ## Footnote Osteoblasts deposit osteoid depending on local metabolic conditions.

Question 44

How can vascularity of delayed union be assessed?

Answer 44

Using Doppler flow or ultrasound Doppler ## Footnote Assessing bone vascularity is more challenging.

Question 45

What is the general treatment approach for delayed unions?

Answer 45

Extended confinement time and continue monitoring bone healing.

Question 46

What is generally preferred when dealing with delayed unions?

Answer 46

Continuing or augmenting the technique used originally.

Question 47

What should be done if there is doubt in managing delayed unions?

Answer 47

Replace external coaptation with an osteosynthesis technique.

Question 48

Under what conditions may the animal be confined for a further period without reoperation?

Answer 48

If fracture stability and vascularity are thought to be satisfactory.

Question 49

What should be done if implants are loose or broken?

Answer 49

They should be removed and the fracture stabilized appropriately.

Question 50

What is strongly recommended if implants are loose or broken?

Answer 50

Add autogenous bone graft.

Question 51

How can a weak plate be reinforced?

Answer 51

Linear external fixator to counteract excessive bending and/or rotational forces.

Question 52

What can be done to reinforce a weak linear external fixator?

Answer 52

By adding more threaded pins and/or a second connecting bar.

Question 53

What may stimulate bone healing when animals are treated with external fixators?

Answer 53

Destabilizing the construct.