4. Musculoskeletal System Flashcards
1
Q
What 4 main cells play a role in bone remodelling?
A
- Osteoprogenitor cell - stem cell
- Osteoblast - matrix-synthesising cell responsible for bone growth
- Osteocyte - mature bone cell which monitors and maintains the mature bone matrix
- Osteoclast - bone-resorbing cell
2
Q
What are the 5 main roles of bones in vertebrates?
A
- Act as primary load-bearing organ (mechanical support)
- Works to protect underlying organs
- Provides a rigid support structure for musculature
- Contributes to calcium and phosphorus homestasis
- Active participant in many endocrine processes
3
Q
What factors determine the ability of bone to resist damage, and subsequent fracture?
A
- Direction of load applied
- Magnitude of load applied
- Rate at which the load is applied
- Species of animal
- Age of animal
- Overall and individual bone health
4
Q
What are the regions of a long bone from proximal to distal?
A
- Proximal epiphyseal bone
- Proximal epiphyseal line (physeal line in immature animals)
- Proximal metaphyseal bone
- Diaphyseal bone
- Distal Metaphyseal bone
- Distal epiphyseal line
- Distal epiphyseal bone
5
Q
What 3 systems deliver blood to a long bone?
A
A. Nutrient artery system - enters the cortex through a nutrient foramen and into the medulla
B. Metaphyseal-epiphyseal system - periarticular vascular plexus arising
C. Periosteal system - supplies outer 1/3rd of bone
6
Q
What are the 5 forces a bone is subject to?
A
- Compression
- Tension
- Shear
- Torsion
- Bending
7
Q
What methods may bone heal via?
A
- Primary or direct bone healing - (1a. contact healing or 1b. gap healing)
- Secondary or indirect bone healing
8
Q
When does primary bone healing occur?
A
Where absolute stability of the fracture occurs, i.e. with anatomic reconstruction, compression of bone fragments and rigid fixation of the bone column
9
Q
What is primary bone healing?
A
Mechanism of healing in which cortical bone attempts to directly re-establish continuity without the formation of a callous
10
Q
What are the two types of primary bone healing?
A
- Contact healing - fracture gap of < 0.01 mm or 10 um, and interfragmentary strain is functionally eliminated at < 2%
- Gap healing - gap must not be > 1 mm
11
Q
Describe the process of primary bone contact healing
A
- direct appostion of fracture ends
- direct remodelling
- cutting cone initiated in fracture region
- reduced radiographic density at bone ends adjacent to the fracture site
12
Q
Describe the process of primary bone gap healing?
A
- small gaps < 1 mm between fracture ends
- minimal movement of fracture site
- lamellar bone forms directly in the fracture gap
- intracortical remodelling through fracture gap and bone restoration occurs
13
Q
What are the stages of secondary bone healing?
A
- Inflammation
- Intramembranous ossification
- Soft callous formation (chondrogenesis)
- Hard callous formation (endochondral ossification)
- Bone remodelling
14
Q
Describe the time periods of secondary bone healing?
A
15
Q
Describe the Salter-Harris fracture system?
A
16
Q
Describe delayed unions, non-unions and malunions?
A
17
Q
What are the 5 key points of fracture description?
A
18
Q
What are the 3 categories of fracture assessment?
A
19
Q
What fixation methods exist for reconstructible (primary bone healing) vs non-reconstructible (secondary bone healing) fractures?
A
20
Q
What are the 4 A’s of fracture assessment?
A
21
Q
Define the terms stress and strain?
A
Stress = the internal force that resists the applied force is called stress
Strain = The deformation of the material caused by the external forces is called strain
22
Q
Is bone stronger in tension or compression?
A
Compression
23
Q
Describe the stress-strain curve, in particular defining the following:
1. Elastic region
2. Plastic region
3. Yield point
4. Toughness
5. Ultimate tensile strength
6. Loading
7. Stress
8. Strain
A
- Elastic Region
Region where the bone can have force applied without injury, i.e. it can be bent as much as you like and return to it’s normal shape - Plastic Region
Region where bone has an increased risk of breaking, and will undergo permanent changes due to applied forces - Yield Point
Point at which the forces applied to bone become too much, and results in permanent changes to the bone. This can be considered the transition point from the elastic to plastic regions on the stress-strain curve. In other words the first point at which the bone cannot return to it’s normal shape. - Toughness
Amount of energy a material can absorb before it reaches a failure point, e.g. how much energy a bone can absorb before it fails. - Ultimate tensile strength
Point at which failure of a material occurs after only one cycle. - Loading
Action of applying a force to an object or material. - Stress
Internal force of a material that resists an applied force, e.g. internal force that resists bending force applied to a tibia. - Strain
Associated deformation or change of a material caused by an internal force.
24
Q
What does a high an low Young’s modulus mean?
A
25
26
List the basic principles of surgical arthrodesis?
1. Careful planning
2. Removal of all cartilage at all sites to be fused
3. Close apposition of the joint surfaces at a functional standing angle
4. Rigid internal fixation using compression
5. Use of cancellous bone graft
6. Careful preservation of soft tissue
27
What is the functional angle of the tarsocrural joint?
Dogs = 134-145 degrees
Cats = 115-125 degrees
28
List the 5 indications for arthrodesis
1. shearing injuries with critical loss of bone
2. instability of the joint
3. painful osteoarthritis that cannot be managed medically, usually following osteochondritis dissecans lesions
4. comminuted fractures of the tarsus
5. failure of the common calcanean tendon (CCT)
29
What surfaces can plates be applied to for tarsal arthrodesis?
* plantar - most biomechanically sound as plate is placed on the tension surface; but rarely used because of the complexity of surgical dissection needed to access the area
* dorsal - most common
* medial - most common
* lateral
30
Why are complication rates so high with sole fusion of the tarsocrural joint alone?
And how can this be mitigated?
List potential complications of arthrodesis.
Lack of available bone stock to secure plate distally without interfering with intertarsal joints.
Change surgical procedure to a pantarsal arthrodesis.
Implant loosening and failure during healing - underestimation of amount of strength of fixation and stabilisation required to facilitate complete fusion. Can augment with intramedullary pins, transarticular screws in lag fashion, and calcaneotibial screws.
Plantar necrosis with loss of soft tissue, including metatarsal pad has been described.
31
Describe the key components of a dorsal tarsal arthrodesis
* craniomedial approach
* medial malleolar osteotomy to provide access to the tarsocrural joint
* articular cartilage removed with a reciprocating saw - much easier to set angle
* standing angle 135 degrees tarsocrural joint
* length of plate allow 4 screws distally into the distal tibia and 2-3 screws in the appropriate metatarsal bone
* can apply a calcaneotibial positional screw through the plate
32
Describe the differences between a dorsal and medial pantarsal arthrodesis
33
What is the reported complication rate for pantarsal arthrodesis?
30-70%
* plate failure - inadequate strength
* plantar necrosis - medial plates
* delayed union
34
What bones contribute to the tarsus?
There are 7 tarsal bones:
- calcaneus (fibular tarsal bone)
- talus (tibial tarsal bone)
- central tarsal bone
- 4th tarsal bone
- 1st, 2nd and 3 tarsal bone
35
How do most injuries occur to the tarsus?
Soft-tissue injuries due to overstress rather than direct injuries from outside forces
Tarsus is more than 3 x the longer than the span of the carpus and subject to propulsive forces generated by the hindlimbs - likely contributes to overstress injuries
36
What are the articulations of the tarsus?
Entire joint = ginglymus (hinge joint)
Majority of movement (90%) expressed only at the tarsocrural articulation.
Six main articulations:
1. tarsocrural
2. talocalcaneal
3. talocalcaneocentral
4. calcaneoquartal
5. centrodistal
6. tarsometatarsal
37
What is the ligamentous support to the tarsus?
Fibrous component of the tarsal joint capsule extends from the distal tibial to the proximal ends of the metatarsal bones and contains within it the soft tissue structural elements of the tarsal joints.
Thickenings over the dorsal and plantar aspects.
38
List the 5 different patterns of central tarsal bone fracture
Type 1 = nondisplaced dorsal slab fracture
Type 2 = displaced dorsal slab fracture
Type 3 = large displaced medial fragment
Type 4 = medial slab fracture with dorsal slab fracture
Type 5 = comminuted fracture
75% of fractures type 4 and 5
39
What is the main difference between a double and triple pelvic osteotomy?
TPO = osteotomies of the pubis, ischium ad ilium
DPO = osteotomies of the pubis and ilium
40
What is the main advantage of a TPO over the DPO?
TPO can reduce magnitude of the force acting on the load-bearing portions of the acetabular rim and the femoral head and increase the contact area on which the force acts.
41
What is the cut-off age for pelvic osteotomy?
1 year, with some authors indicated 10 months of age.
There is no published evidence to suggest that pelvic osteotomy is ineffective in skeletally mature dogs with hip joint laxity.
42
List the basic components of ESF and why it is growing in popularity.
Connecting clamp
Connecting bar
Fixation pins
Shift towards favouring adequate and relative stability with diligent preservation of local soft tissues to avoid vascular compromise
43
What are the types of ESF pins and describe major advantages of each type?
1. Positive profile - cortical vs cancellous thread
- greater stiffness, greater axial pull-out strength, greater fatigue life compared to smooth pins
2. Negative profile -
Further classified as full or half pins. Both will penetrate the cis and transcortex, but the penetration of soft tissues will alter.
44
Why are larger shaft diameters advantageous in ESF systems?
Increased AMI, resistance to bending or failure with cyclic loading
More stable at the pin-clamp interface
45
What are the three main types of ESF systems?
1. Linear ESF = three basic components being pins, connecting bars and clams
2. Free-form ESF = subtypes of linear ESFs where clamps are replaced by epoxy putty
3. Circular and hybrid ESF = ring fixators and/or linear/ring fixators
46
What are the advantages of ESF systems?
47
What are the disadvantages of ESF systems?
48
What are the safe corridors for ESF pin placement on the long bones of the dog?
49
What are the 3 types and sub-types of ESF applications?
50
What change does a TPLO cause in regards to the femoral contact area?
TPLO causes this to be more caudal
51
What 1 of 3 CrCL functions does a TPLO procedure address?
What 2 functions does it not address?
1. Neutralising cranial tibial subluxation
does not
2. prevent internal tibial rotation
or
3. prevent stifle hyperextension
52
What two points determine the tibial long axis or mechanical axis?
1. Centre of the intercondylar tubercles of the tibia
2. center of rotation on the talus
53
What 5 points can the osteotomy be centered on for a TPLO procedure?
1. Cranial tibial plateau point
2. Caudal tibial platea point
3. proximal tibial long axis point
4. distal tibial long axis point
5. over the centre of the intercondylar tubercles
54
What is the most anatomically correct position to center a TPLO rotation point?
Centered position over the center of the intercondylar tubercles
55
