2 MSK Fractures Flashcards
What are the physical forces that must be overcome to allow bones to heal? (5)
- Tensile force
- Axial compression
- Shear forces
- Bending
- Twisting/Torsion
These forces must be addressed in the healing process to ensure proper bone union.
What type of healing occurs in a DCP in compression mode for a closed mid diaphyseal transverse femoral fracture?
Direct bone healing
This involves anatomic reconstruction and may include gap healing occurring simultaneously.
What mnemonic can be used to remember the Salter-Harris fracture types?
SALTR
Straight across
Above
lower
Through/two
cRush
Each letter corresponds to a different fracture type.
What characterizes Salter-Harris Type I fractures? (5)
- Straight across
- 5-7%
- Fracture plane passes through the growth plate, not involving bone
- Cannot occur if the growth plate is fused
- Good prognosis
This type is the least severe and has a high chance of healing well.
What characterizes Salter-Harris Type II fractures?
- Above
- ~75% (most common)
- Fracture passes across most of the growth plate and up through the metaphysis
- Good prognosis
This type is often seen in pediatric fractures.
What characterizes Salter-Harris Type III fractures?
- Low/Below
- 7-10%
- Fracture plane passes along the growth plate and down through the epiphysis
- Poorer prognosis due to interruption of proliferative and reserve zones
This type can lead to long-term growth issues.
What characterizes Salter-Harris Type IV fractures?
- Through or Together
- Intra-articular
- 10%
- Fracture plane passes through the metaphysis, growth plate, and down through the epiphysis
- Poor prognosis due to interruption of proliferative and reserve zones
These fractures are more complex and often require surgical intervention.
What characterizes Salter-Harris Type V fractures?
- Ruined or Rammed, or cRushed
- Uncommon <1%
- Crushing type injury that does not displace the growth plate but damages it by direct compression
- Worst prognosis
These fractures can severely impact growth and development.
What are prognostic indicators for Salter-Harris fractures? (5)
- Whether growth plate is damaged
- Which bone is involved (e.g., tibia vs ulna)
- Mechanism of injury
- Timing and accuracy of reduction/fixation
- Age at which fracture occurs- how much more growth potential there is
Understanding these indicators can help predict long-term outcomes.
In which microanatomic zone does most fractures occur at the physis?
Hypertrophic zone
This zone is structurally the weakest part of the growth plate because it has very little matrix, decreased type 2 collagen, increased type X.
What are the 4 microanatomic zones of the physis - from metaphysis to epiphysis
- provisional zone of calcification
- zone of maturation/hypertrophy
- Proliferative zone
- Reserve zone
What are the cellular responses during distraction osteosynthesis? (4)
and what process does it mimic?
Bone becomes metabolically activated under traction, leading to:
1. * Increased angiogenesis
1. * Formation of a hematoma
1. * Formation of a procallus
1. * Production of new bone trabeculae without a cartilaginous step
This process mimics intramembranous ossification.
What are two clinical examples where distraction osteosynthesis is used?
- Correcting congenital angular limb deformities
- Correcting limb length secondary to premature growth plate closure issues (after traumatic injury)
- limb sparing surgeries
These conditions often arise in breeds with specific conformation issues.
What 2 main factors contribute to fracture non-union?
- Lack of adequate stability (mechanical)
- lack of blood supply (biological)
Understanding these factors is crucial for effective treatment.
What are the types of viable fracture non-unions? (3)
- Hypertrophic (Elephant’s foot)
- Moderately Hypertrophic (Horse’s hoof)
- Oligotrophic
Each type has distinct characteristics visible on radiographs.
Radiographic signs of a Fracture non union (3)
- Visible fracture gap
- clearly defined fracture ends
- (possibly) a callus that doesnt bridge the gap
Biological factors that impact blood supply and bone healing
- soft tissue envelope: location of fracture, breed/size
- degree of trauma to soft tissue envelope
- older vs. younger animals:
- Infection
older animals have impaired callous bridging and increased resorbtion through osteoclast activity, decreased osteoblast responses, delayed chondroblast differentiation.
Infection retards healing through inflammation, apoptosis of osteoblasts and increased osteoclast activity.
What are the properties of bone grafting for non-union fracture repairs?
- Osteoinduction
- Osteogenesis
- Osteoconduction
- Osteopromotion
These properties enhance the healing process and promote new bone formation.
how does infection affect bone healing?
Infection retards healing through inflammation, apoptosis of osteoblasts and increased osteoclast activity.
What are the three sites for harvesting autogenous cancellous bone grafts?
- Proximal humerus
- Dorsal wing of ilium
- Proximal tibia
These sites provide suitable graft material for bone repair.
Mechanical factors that affect bone healing
- Choice of fixation: either not enough stability - too much strain
- Too much stability; osteoporosis and resorbtion of bone if implant is taking all the load
Bones remodel depending on the forces they are exposed to (Wolffs law)
What characteristierdcs define direct bone healing? (4)
- Healing with fractured ends apposed in compression
- no gap, but may involve gap healing (<1mm)
- no strain
- no callus formation
This process involves Haversian remodeling and is efficient when conditions are optimal.
What are characteristics of indirect bone healing? (4) and 5 main stages?
- small fracture gaps
- variable strain,
- Callus formation
- Endochondral bone healing
involving multiple overlapping stages
1. * Inflammatory
1. * Intramembranous ossification
1. * Soft callus formation
1. * Hard callus formation (endochondral ossification)
1. * Remodeling
This type of healing is more common and complex.
What is Haversian remodelling?
One way that bone adapts to its mechanical environment - a repair process in which existing bone is resorbed and replaced by new bone.
Cutting cones composed of osteoclasts and osteoblasts advancing across the fracture plane, cutting a channel into the bone and laying lamellar bone parallel to the long axis of the diaphysis. There is simultaneous resorption and deposition.
Tissues that can tolerate:
100% strain
10% strain
2-10% strain
<2% strain
100% strain- Granulation tissue
10% strain - Cartilage
2-10% strain - Woven bone
<2% strain - Lamellar bone
Define malunion in the context of fracture healing.
Fully healed fractures where anatomical alignment has not been correctly achieved
This can lead to limb deformities and functional issues.
Define delayed non-union in the context of fracture healing.
A fracture that may have formed a callus but is taking longer than expected to heal
This condition can lead to complications if not addressed.
What biomechanical factors may contribute to delayed fracture healing? (2)
- Instability/poor fixation choice/too much strain
- Large defects (excessive fracture gaps)
These mechanical issues can impede proper healing and require careful consideration during treatment.
If too much strain healing wont progress past cartilage formation.
What are the biological factors that may contribute to delayed fracture healing? (3)
- Poor blood supply: damage, distal limb (poor soft tissue envelope)
- infection,
- intrinsic patient factors (older patients, comorbidities ie. diabetes/cushings)
Damage to area affects nutrient and oxygen supply necessary for osteosynthesis
What is the resting zone in the microanatomic zones of physis and types of cells it contains?
AKA Reserve zone, Closest to epiphysis, contains hyaline cartilage matrix and small oval chondrocytes
Describe the proliferative zone in the physis.
Resting chondrocytes transition to actively mitotic chondrocytes, characterized by stacked coin appearance and less matrix made of Type II collagen
What occurs in the hypertrophic zone of the physis?
Chondrocytes hypertrophy and undergo apoptosis. Reduction of Type II collagen, and and increased Type X collagen provides stiffness and prevents nutrient diffusion leading to hypoxia and thus stimulation of vascular angiogenesis.
Structurally the weakest section. Predisposed to Type 2 Salter Harris fractures in young animals.
What is the role of the mineralisation/calcification zone in the physis?
Chondrocytes undergo apoptosis and matrix mineralisation occurs, scavenging calcium and phosphorus from adjacent tissues
Further vascular invasion removes calcified cartilage and debris.
What happens in the zone of ossification?
Osteoblasts deposit woven bone, following vascular networks, and osteoclasts remodel into lamellar bone over time (Haversian remodelling)
What is a Type 1 Salter Harris injury?
Straight across the growth plate
What is a Type 2 Salter Harris injury?
Across and above the growth plate line through the metaphysis
Why is distal ulnar physeal trauma clinically significant?
The conical distal physis most commonly injured - Responsible for 85-100% of ulnar growth and attached to radius by a ligament in the middle, so damage to physis leads to significant angular limb deformities/elbow incongruity. The radius tends to bow around the ulna, increasing load on radial head and anconeal process.
most common growth plate injury in dogs (63%),
The conical shape is vulnerable to force from any direction, unable to shear regardless of type of force.
What is the most common growth plate injury in dogs?
Premature closure of the distal physis due to Type 5 Salter Harris injuries
What is osteoinduction?
Transfer of undifferentiated mesenchyma into osteoblasts, initiated by TGF-b and Bone morphogenic protein
What does osteogenesis refer to?
Formation of new bone by supplying osteoblasts and osteoclasts
Define osteoconduction.
Provision of a 3D porous structure that allows adherence and proliferation of cells, and vascular ingrowth
What is osteopromotion?
Substances like platelet-rich plasma that enhance proliferation and differentiation of mesenchymal stem cells
Where can bone grafts be harvested from? (3)
which is easiest to access?
Proximal humerus, dorsal iliac wing, proximal tibia
Proximal tibia is often preferred for ease of access
What are causes of delayed non-unions?
Lack of good blood supply, infection, too large fracture gap, lack of stability
Specific examples include damage to blood supply from trauma or fixation method
What is the treatment plan for a dystrophic or early atrophic non-union?
- Remove implants,
- Debride bone ends,
- Flush,
- Take bacterial culture,
- Graft with autologous cancellous bone
This stimulates the bone healing process and promotes blood supply
What type of healing occurs with LCP in compression mode?
Direct healing, where bone ends are placed in compression to remove the fracture gap
What type of healing occurs with external skeletal fixation (ESF)?
Endochondral ossification, secondary bone healing process without disturbing the initial hematoma
What challenges do toy breeds face in distal antebrachium healing?
Poor tissue envelope, decreased vascular density, difficulty establishing bone apposition
These factors complicate healing and increase risk of osteonecrosis
What are the risks associated with rigid stabilization in toy breeds?
Osteopenia due to stress reduction, necessitating sequential screw removal
what is this type of plate?
DCP
Dynamic Compression Plate
type of plate?
LCP plate
Locking compression plate
type ?
LC-DCP
Low contact, dynamic compression plate
Down side of Direct bone healing?
Slower healing
