Chapter 3 Flashcards
What is unique about fracture healing compared to soft-tissue healing?
Fracture healing can be completed without the formation of a scar.
What does the presence of tissue other than bone in a fracture gap indicate?
It represents incomplete healing.
What dictates the pattern of fracture repair if adequate vascularity is present?
The biomechanical environment.
What must occur before bone can be produced during fracture healing?
Restoration of mechanical stability.
What are the two methods by which mechanical stability can be achieved during fracture healing?
- Natural healing process
- Osteosynthesis
What is the healing of unstable fractures characterized by?
Formation of an intermediate callus prior to bone formation.
What is the term for the type of healing that involves the formation of an intermediate callus?
Indirect or secondary healing.
How many overlapping phases are there in the indirect healing process?
Three phases: inflammation, repair, and remodeling.
What determines the amount of callus produced during fracture healing?
The stability of the fracture.
What is interfragmentary strain?
Deformation occurring at the fracture site relative to the size of the gap.
Deformation: The action or process of changing in shape or distorting, especially through the application of pressure.
What is the maximum interfragmentary strain that allows for bone formation?
Lower than 2%.
What processes occur to overcome unfavorable conditions in spontaneous healing of complete fractures?
- Initial contraction of muscles surrounding the fracture
- Resorption of fragment ends
- Orderly repair with suitable tissues
- Formation of a prominent external callus
How long does the inflammatory phase of fracture healing typically last?
3–4 days or longer, depending on the force that caused the fracture.
What is a key clinical sign that indicates the end of the inflammatory phase?
A decrease in pain and swelling.
What occurs due to the disruption of medullary vessels after a fracture?
Extravasation of blood and ischemic necrosis of bone.
What type of clot forms at the fracture site to initiate spontaneous fracture healing?
A fibrin-rich clot.
What did Ham observe regarding the fracture repair process in 1969?
Much of the repair process took place around, rather than within, the interfragmentary hematoma.
What is the histological characteristic of ischemic necrosis of bone?
Presence of empty lacunae.
What influence does interfragmentary strain have on fracture healing?
It influences the type of tissue that forms in the fracture gap.
What fills the defect during the inflammatory phase of secondary bone healing?
Hematoma.
What replaces the hematoma in the repair phase?
Granulation tissue.
What type of callus is formed during the remodeling phase?
Fibrocartilaginous callus.
What leads to the formation of a hard callus?
Mineralization.
True or False: The hematoma can act as a scaffold for cells during bone healing.
True.
What do growth factors released by the hematoma stimulate?
Angiogenesis and bone formation.
What has been found to induce endochondral bone formation in ectopic sites?
Transplantation of fracture hematoma.
What are the first sources of mitogenic factors at a traumatized site?
mitogenic factor- a substance or signal, that induces or stimulates cell division (mitosis)
Platelets
Which two growth factors do platelets release that stimulate bone production?
- Platelet-derived growth factor (PDGF)
- Transforming growth factor-β1 (TGF-β1)
What mediates the angiogenic properties of fracture hematoma?
Vascular endothelial growth factor (VEGF).
What role do inflammatory mediators like prostaglandins E1 and E2 play during bone healing?
Prostaglandins are lipids (fats) with hormone-like effects, while cytokines are proteins
They may stimulate angiogenesis and signal early bone resorption.
What type of cells are abundant during the inflammatory phase and contribute to new vessel formation?
Mast cells.
Fill in the blank: Within hours, a transient extraosseous blood supply emerges from surrounding _______.
soft tissues.
What assists in the removal of necrotic bone and aids in the construction of the callus?
Mononuclear phagocytes.
Mononuclear phagocytes are a group of cells that includes monocytes, macrophages, and dendritic cells.
The are part of the mononuclear phagocyte system (MPS), are specialized cells derived from bone marrow progenitor cells that playing a crucial role in immunity and tissue homeostasis by engulfing foreign substances and initiating immune responses.
What is resorption of fragment ends?
It is particularly obvious in spontaneous fracture healing when the fracture gap widens, lowering interfragmentary strain and minimizing deformation of local tissues.
This process is essential for proper healing and stability of fractures.
What role do macrophages play in fracture repair?
- Orchestrate the orderly sequence of cutaneous wound healing
- Contain growth factors that initiate fibroplasia in soft tissue and bone repair.
Key growth factors include fibroblast growth factor (FGF).
What effect does a muscle flap have on angiogenesis?
It enhances angiogenesis and improves healing of experimental tibial osteotomies in dogs.
This demonstrates the significance of surrounding soft tissues.
What happens to the hematoma during the healing process?
It is resorbed by the end of the first week unless infection, excessive motion, or extensive necrosis of surrounding soft tissues persist at the fracture site.
The hematoma is a critical initial component of fracture healing.
What begins the transformation of a hematoma into granulation tissue?
Capillary ingrowth, along with mononuclear cells and fibroblasts, begins this transformation within a few days.
This marks the initial stage of the repair phase.
What is the tensile strength of granulation tissue?
It can withstand a tensile force up to 0.1 Nm/mm2.
This contributes to the mechanical strength during early healing.
What type of collagen predominates in mature connective tissue?
Type I collagen predominates as the maturation process continues.
Types I, II, and III collagen are initially deposited.
What influences the development of a cartilaginous callus?
- Low oxygen tension
- Poor vascularity
- Growth factors
- interfragmentary strain.
These factors are critical during the repair phase.
What role do mesenchymal cells play during the inflammatory phase?
They proliferate and differentiate into chondrocytes during the repair phase.
This process is crucial for tissue formation within the fracture gap.
What is the significance of TGF-β and BMPs in fracture healing?
TGF-β (Transforming Growth Factor-β)
BMPs (Bone Morphogenetic Proteins)
They orchestrate chemotaxis, proliferation, coordination, and differentiation of stem cells into chondrocytes or osteoblasts.
These growth factors are essential for orderly tissue formation.
What happens to the periosteum surrounding the fracture site?
It thickens prior to undergoing chondrogenic transformation, producing an external callus vascularized by extraosseous vessels.
This is important for the stability of the healing fracture.
What characterizes the internal callus?
It develops from the endosteal cell layer and is confined to the medullary canal, receiving blood supply from medullary arterioles.
The internal callus is critical for healing within the bone.
What constitutes the ‘bridging callus’?
The external callus and the internal callus together constitute the ‘bridging callus’.
This structure is essential for stabilizing the fracture site.
What is the tensile strength of the early ‘soft callus’?
Its ultimate tensile strength is 4–19 Nm/mm2.
This strength is similar to that of fibrous tissue.
Compared to granulation tissue having 0.1 Nm/mm2 strength
Fill in the blank: The repair phase of secondary bone healing includes: _______.
hematoma, granulation tissue, connective tissue, cartilage, cartilage mineralization, woven bone formation.
These stages are critical for successful fracture healing.
What is the role of the external callus in fracture healing?
Enlarges the cross-sectional diameter of the fracture, increasing resistance to bending and decreasing interfragmentary strain.
What is restored during the remodeling phase of fracture healing?
The medullary cavity is restored and woven bone is replaced by cortical bone.
How does the strength efficiency of a bone increase with the distance to the neutral axis?
Strength efficiency increases by the third power of the distance.
Rigidity increases by the 4th power
What contributes to the stiffening of the interfragmentary gap?
Increasing proteoglycan concentrations within the fibrocartilage.
What is the process that leads to the formation of a hard callus?
Mineralization of the soft callus proceeds from the fragment ends toward the center of the fracture site.
True or False: Chondrocytes initiate and control the formation of mineralized clusters in fracture healing.
True.
What do mitochondria in the fracture gap accumulate that aids in calcification?
Calcium-containing granules.
What closely resembles the steps of bony substitution at the fracture site?
Endochondral ossification.
What type of bone formation can occur in fibrous tissue within the fracture gap?
Intramembranous (direct) bone formation.
What is the ultimate tensile strength of compact bone?
Around 130 Nm/mm2.
What is the modulus of elasticity of compact bone?
10,000 Nm/mm2.
The modulus of elasticity, also known as Young’s modulus, measures a material’s stiffness or resistance to deformation under stress, essentially how much it stretches or compresses when a force is applied
Do the fracture site at the end of the repair phase differs from that of the original bone?
Yes
What factors influence the time required to achieve bone union?
Fracture configuration and location, status of adjacent soft tissues, patient characteristics.
How long may the remodeling phase last in humans?
6–9 years.
What phenomenon governs the balanced action of osteoclastic resorption and osteoblastic deposition?
Wolff’s law.
What effect does axial loading of long bones have on osteoclastic and osteoblastic activity?
Electropositive convex surface predominates osteoclastic activity; concave surface has increased osteoblastic activity.
What is required for the progression from soft to hard callus in spontaneous fracture healing?
Adequate blood supply and gradual increase in stability at the fracture site.
What can happen if there is compromised vascularization and excessive instability in a fracture?
Formation of fibrous tissue and development of an atrophic nonunion.
What can occur if the fracture gap is well vascularized but there is uncontrolled interfragmentary motion?
Development of a hypertrophic nonunion or pseudoarthrosis.
What frequently results from the initial displacement of bone fragments due to trauma and muscle contraction?
Malunion
At the end of what phase can there be low impact exercises?
Repair phase
What is the pattern of healing under restricted motion in fractures?
Intermediate to biological immobilization by a callus formed in spontaneous healing and callus-free repair after absolute stabilization.
What does fracture healing after external coaptation resemble?
Spontaneous bone repair
Closed reduction helps to minimize malaglignment of fragments
What is a characteristic of gliding implants such as intramedullary pins and nails?
They typically allow some motion.
What effect do intramedullary implants have on medullary blood flow?
They temporarily disturb medullary blood flow.
What is the consequence of reaming the medullary canal?
It interferes with the vascularization of the inner cortex.
What was the effect of unreamed nails on blood supply in experimental tibial fractures?
Unreamed nails caused a 30% attenuation in blood supply compared to 70% in the reamed procedure.
How do external fixators affect blood supply to healing bone?
They interfere minimally with the blood supply.
What factors influence the amount of callus produced in external fixation?
Fracture configuration and the rigidity of the frame applied.
Under what conditions may callus formation occur after plate fixation?
When the implant is not on the tension side, fracture reduction is imperfect, or the plate lacks rigidity.
What is the focus of biological fixation in comminuted fractures?
Biological factors over anatomical reduction and mechanical stability.
What is a bridging plate used for in fracture fixation?
Applied across the fracture gap, spanning the entire length of the bone.
How does the stability of a bridging plate compare to a traditional compression plate?
Less stable, resulting in increased callus production.
What was observed in a study regarding bone density and osteogenesis 12 weeks after applying either a bridging plate, an intramedullary nail, or an external fixator compared to lag screws and compression plate?
Increased
What are the benefits of biological fixation of comminuted fractures?
Increased callus production, accelerated radiographic union, earlier gain in biomechanical strength, earlier return to function.
What is the term used for the mode of repair where there is a lack of callus formation between bone fragments?
Primary healing
First noted by Danis in 1949
What is the primary way healing occurs in primary healing?
Direct filling of the fracture site with bone
Without formation of mechanically relevant periosteal or endosteal callus
What type of implants achieve stable interdigitation of bone fragments?
Rigid, nongliding implants
Such as compression plates or lag screws
What is the impact of precise reduction and rigid fixation on biological signals in fracture healing?
Eliminates biological signals that attract osteoprogenitor cells
Contributing to callus formation in secondary healing.
Osteoprogenitor cells, also known as osteogenic cells, are the stem cells of bone, derived from mesenchymal stem cells, and are crucial for bone repair, growth, and remodeling, differentiating into osteoblasts and osteocytes.
What is the maximum interfragmentary strain for contact healing to occur?
Less than 2%
With a defect between bone ends less than 0.01 mm
What initiates the process of contact healing?
Formation of cutting cones at the ends of the osteons closest to the fracture site
What are the roles of osteoclasts and osteoblasts in contact healing?
Osteoclasts create longitudinally oriented cavities, osteoblasts produce osteoid
This occurs simultaneously with bony union and Haversian remodeling
What is the rate at which cutting cones progress across the fracture site during contact healing?
50–100 µm/day
How does gap healing differ from contact healing?
In fracture healing, contact healing occurs with direct bone contact, leading to simultaneous bone union and remodeling.
While gap healing, with a small gap (less than 1 mm) between bone ends, involves separate, sequential processes of union and remodeling.
What is the size range of gaps for gap healing to occur?
Less than 800 µm to 1 mm
What type of bone formation is involved in gap healing?
Intramembranous bone formation
lamellar bone deposition
What is the characteristic orientation of newly formed lamellar bone in gap healing?
Perpendicular to the long axis
What occurs after the initial lamellar bone formation in gap healing?
Secondary osteonal reconstruction
What happens to the vascular loop during gap healing?
It grows into the gap and carries osteoprogenitor cells that differentiate into osteoblasts
What is the mechanical quality of the area united by lamellar bone in gap healing?
Mechanically weak
Due to poor connection to adjacent intact cortex
When does Haversian remodeling typically begin in gap healing?
Between 3 and 8 weeks
Haversian remodeling is a process where existing bone tissue is resorbed (broken down) and replaced by new bone tissue, forming interconnected, cylindrical structures called secondary osteons, which are crucial for bone adaptation and repair.
What do osteoclasts form during Haversian remodeling in gap healing?
Longitudinally oriented resorption cavities
What is the result of the advancement of cutting cones during Haversian remodeling?
Unites new lamellar bone deposited in the gap to each fragment end
What is the end goal of the processes involved in gap healing?
Restoration of anatomical and mechanical integrity of the cortex
How does biological fracture fixation differ from the biomechanical approach?
Biological fracture fixation aims for overall length and alignment restoration while limiting surgical manipulation.
What is the preferred method for fracture reduction in biological fixation?
Closed fashion or limited exposure to minimize disruption of the fracture hematoma and soft tissues.
What types of implants are preferred in biological fracture fixation?
- External fixators
- Locked intramedullary nails
- Circular ring fixators
Which fractures are especially applicable for biological fracture fixation?
Distal limb fractures, humeral and femoral fractures.
What is the ‘biological plating technique’?
An approach with indirect fracture reduction and an ‘open-but-do-not-touch’ strategy prior to bone grafting.
What is the purpose of autogenous cancellous bone grafts?
To stimulate healing of fracture gaps and promote rapid bone formation.
Shortcoming of the autogenous cancellous graft is its lack of biomechanical strength. This precludes its use as a structural graft.
What are the most common donor sites for autogenous cancellous bone grafts?
- Proximal humerus
- Iliac crest
- Proximal tibia
What is the gold standard bone graft used?
autogenous cancellous bone graft
What is the resorption time for medical grade calcium sulfate?
2–5 weeks in animals
4–8 weeks in humans.
What is Hydroxyapatite (HA) and Tricalcium phosphate (TCP)?
Hydroxyapatite (HA) and tricalcium phosphate (TCP), particularly β-TCP, are both calcium phosphate compounds commonly used in bone repair and regeneration, with HA being the mineral component of natural bone and β-TCP exhibiting faster biodegradation.
What is the role of osteoconductive materials in bone graft substitutes?
Act as scaffolds onto which osteoprogenitor cells can lay new bone.
What is the main goal of osteoinductive bone graft substitutes?
To initiate and stimulate the differentiation of undifferentiated mesenchymal cells into osteoprogenitor cells.
True or False: Banked demineralized bone matrix (DBM) is both osteoconductive and osteoinductive.
True.
demineralized bone matrix (DBM)
Fill in the blank: The incidence of complications associated with collection of autograft in small animals has not been reported, but the morbidity rate approaches ____ in humans.
25%
with major complications in 3–4% of patients [66, 67]. Complications include pain, sepsis, stress fractures, intraoperative blood loss, increased surgical time, and limited supply.
What is a common complication associated with large allograft segments?
Incomplete resorption, leading to fatigue failure and infections.
What is a key feature of calcium phosphate cements?
They can be molded or injected into defects and harden at body temperature.
What is the primary method of sterilization for allogenic bone to preserve osteoinductive properties?
Chemical sterilization combined with the demineralization process.
Why are osteoinductive implants attractive in certain cases?
Especially attractive in cases with compromised healing capacities, such as nonunions
Do synethetic bone agents carry any risk of disease.
No
How many BMPs have been identified since 1988?
Bone morphogenetic proteins (BMPs) are a group of growth factors that play a crucial role in bone formation, repair, and maintenance. They belong to the transforming growth factor-beta (TGF-β) superfamily of proteins.
At least ten BMPs
Which two BMPs have been particularly well described in humans?
Recombinant BMP-2 and BMP-7 (OP-1)
Bone morphogenetic proteins (BMPs) are a group of growth factors that play a crucial role in bone formation, repair, and maintenance. They belong to the transforming growth factor-beta (TGF-β) superfamily of proteins.
What is a benefit of synthetic agents compared to bone-derived products?
Do not carry any risk of disease
What must osteoinductive proteins be combined with to be effective?
A biocompatible carrier
A biocompatible carrier is a material used to transport or deliver substances (like drugs or genes) into the body without causing harm or unwanted reactions.
What should guide the selection of a therapeutic strategy for bone healing?
Assessment of the factors affecting bone healing
What is a classic example of combining biomechanical and biological strategies for treatment of nonunions?
Internal fixation and autogenous grafting
What combination may be justified for highly comminuted fractures in human diabetics?
Allograft as an osteoconductive gap filler mixed with a gel of demineralized bone matrix
What does calcium sulfate slow down when manufactured as medical-grade pellets?
Rapid degradation rate and antibiotic release rate
What is characterized radiographically by a gradual disappearance of the fracture line?
Direct fracture healing
What characterizes direct fracture healing radiographically?
A gradual disappearance of the fracture line without the formation of an external callus.
Is there resorption of the fragment ends in direct fracture healing?
No, there is no resorption of the fragment ends.
What happens to the fracture site during direct healing?
The zone around the fracture loses radiopacity.
What is the typical duration for complete remodeling in direct fracture healing?
A few months to a few years, depending on the species.
What type of healing is expected after external coaptation or semi-rigid internal fixation?
Indirect or secondary bone healing.
What is the initial radiographic sign of indirect bone healing?
Local loss of radiopacity and widening of the fracture gap.
When does callus formation become apparent radiographically in indirect healing?
Once mineralization proceeds.
What forms first in the callus during indirect healing?
The periosteal component.
How long after repair can a calcified callus be seen?
10–12 days after repair.
How does the age of the patient affect callus formation?
It affects both the speed and appearance of the callus.
What happens to osteoprogenitor cells in immature animals during periosteal stripping?
They get pulled with the periosteum, producing a callus away from the bone.
What effect does local hypoxia have on mesenchymal cells?
It encourages differentiation into chondrocytes rather than osteoblasts.
What happens to the fracture line and gap as the fibrocartilaginous callus matures?
The fracture line disappears and the fracture gap gains radiopacity similar to adjacent bone.
What is the purpose of obtaining serial radiographs every 4–6 weeks?
To assess implant stability, verify alignment, confirm absence of complications, and monitor healing.
What is the most common radiographic sign used to assess fracture healing according to a survey of orthopedic surgeons?
Cortical continuity.
What are some factors affecting fracture healing?
- Age of the patient
- Type of fracture
- Local blood supply
- Tissue oxygenation
- Interfragmentary strain.
What are the expected radiographic signs indicating normal secondary healing in dogs?
- Widening of the fracture gap and smudging of fracture edges at 5–7 days
- Appearance of a bony callus at 10–12 days
- Disappearance of the fracture line within 30 days
- Complete remodeling of the callus 90 days after repair.
What type of fractures heal slower?
Fractures of compact bone, particularly in sparse or compromised soft tissue.
What is the expected healing time for locked intramedullary nails and external fixation?
- Locked intramedullary nails: 14–19 weeks
- External fixation: 14–18 weeks.
What is the relationship between the regenerative capacity of mammalian bone and its position on the phylogenic scale?
It is inversely proportional.
What was the mean time for first radiographic evidence of bony bridging in a study of femoral comminuted fractures in dogs?
15 weeks for traditional plating and 10 weeks for bridging plates.
What remains subjective despite well-described radiographic signs of fracture healing?
The interpretation of these signs.
Deciding when to intervene for slow-healing fractures is described as what?
Something of an art.
What is the primary reason for implant removal in younger patients?
To prevent changes associated with stress protection and to decrease the risk of fracture at the junction between the plate and the bone
Stainless steel plates have a greater coefficient of elasticity than bone, which can induce bone atrophy.
What are the indications for plate removal?
- Osteomyelitis
- Pain on palpation of the plated bone
- Radiographic evidence of osteopenia
- Lameness associated with cold transmission through metal
Plating of long bones with limited soft-tissue coverage may warrant plate removal.
What is the most common indication for implant removal in small animals?
Related to the use of external fixators
Timing of implant removal varies with the fracture assessment score and the type of healing expected.
What is the average time range for fixator removal in various studies?
4 to 32 weeks, with a mean of about 15 weeks in comminuted fractures of the tibia and radius
Experimental data support gradual disassembly of external fixators to encourage callus formation.
Define primary bone healing.
The biological response to anatomical reduction and stability without the formation of callus
Fractures undergoing primary healing are initially weaker than those united by callus.
How long does it take for the cortex to recover its internal architecture after primary healing?
About 18 months in mature diaphyseal bone
The remodeling phase can be prolonged by various factors.
What factors can prolong the remodeling phase of bone healing?
- Age and health of the patient
- Degree of comminution and devitalization of the fracture
- Accuracy of the reduction
- Stability of the fixation
- Adjuvant treatments
Bone grafts act as positive adjuvants while immunosuppressive drugs or chemotherapy can have adverse effects.
What should not be excised following plate removal and why?
The ridges commonly found on each side of the plated area, as they contribute to the mechanical integrity of the treated bone
However, screw and pin holes act as stress risers.
What is recommended regarding loading applied to a weight-bearing bone after implant removal?
Restrict the amount of loading for about 6 weeks after removal
This is becuase screw wholes can be stress risers after.
Exercise should be restricted, and occasionally splints are indicated to protect the weakened bone.
True or False: The plate should be removed prematurely during direct bone healing.
False
The plate functions to protect the bone during direct bone healing.
Fill in the blank: The timing of implant removal varies with the _______ and the type of healing expected.
[fracture assessment score]
