Small animal ortho Flashcards
What does kyphosis mean
Dorsal curvature of the spin
True kyphosis = a deformity vs false kyphosis = due to pain
What is scoliosis
Lateral curvature of the spine
What is valgus
Lateral deviation of the distal portion of the limb
What is varus
Medial deviation of the distal portion of the limb
What is palmigrade and platigrade
Palmigrade = all parts of manus flat against ground
Plantigrade = all parts of pes flat against ground
What is truncal sway and what might cause it to be increased or decreased
= movement of the spine/pelvis when walking
> Increased with hip pain to avoid flexing hip
> Decreased with spinal pain
Signs of thoracic limb lameness
Weight shifted caudally **
Head not; down on sound **
Shortened strides
Faster swing phase on sound leg; so shorter stance phase on lame one
May circumduct limbs
Abnormal tracking
Signs of pelvic limb lameness
Weight shifted cranially**
Hip hike; increased vertical movement in the lame leg i.e higher on lame side
May bunny hop with hip pain
Increased truncal motion with hip pain
Limb circumduction
How do we grade lameness
0 = sound
1= mild; hard to spot
2 = moderate; normal stride length and partial weight bearing
3 = moderate; shortened stride length and partial weight bearing
4 = severe lameness; toe touch weight bearing, minimal use of the limb
5 = non weight bearing lameness
How should weight be distributed between legs (objective gait analysis)
Symmetrical
Thoracic limbs take 60% of weight, pelvic limbs take 40%
What markers do osteoblasts express
What about osteoclasts
Blasts = ALP, OC
Clasts = TRAP and cathepsin K
What are the two mechanisms of bone development
Endochondral ossification
Intramembranous ossification
What is the key difference between endochondrial ossification and intramembranous bone formatino
With endochondral ossification, there is a cartilage model made first which is resorbed and replaced with bone –> important in long bone growth and fracture healing
Intramembranous has no chondral elements; important in circumferential bone growth
What is the immature and mature bone structure
Immature = woven bone; haphazard connections
Mature = lamellar
What is plexiform bone
Special form of bone that is rapidly formed and brick-like
Seen in young, fast growing animals e.g pigs, ruminants, horses and can be remodelled to lamellar bone
Structure of cancellous bone
Vertical plates
Horizontal rods so strength in multiple directions
High surface area allows it to be resorbed and formed very quickly to mobilise and store minerals
What type of bone is the spine rich in
Cancellous
What are diaphysis, epiphysis, metaphysis
Shaft of lone bone = diaphysis
End = epiphysis
Region between the two = metaphysis
Bone turnover cycle
Driven by osteoclast action releasing growth factors from bone matrix (e.g TGF-beta)
This causes recruitment of osteoblasts, get osteoid formation, then mineralisation
What is Wolff’s law in bone remodelling
Bone struture remodels according to the loads it is exposed to; aligning on lines of principle stress
Loading stimulates net formatino
What are the 3 phases of fracture healing
Inflammatory stage = shortest
Repair stage
Remodelling stage = longest
What des comminution of a fracture refer to
Degree of fragmentation
What is primary bone healing
Bone healing which does not involve callus formation
May be contact or gap healing
- Gap healing = when fragments not in direct contact but within 1mm of each other
Cause of acromegaly
Excess growth hormone from the pituitary
= acquired disease; more common in males
get increase in bone formation leading to broad head and large clubbed paws
What is a pituitary dwarf
Animal which has a congenital lack of growth hormone
What can excess thyroid hormone lead to in relation to bones
Osteoporosis secondary to increased metabolic rate
What are thyroid hormones involved in with bone formatino
Cartilge maturation
Stages of endochondral ossification (NB: only get this in long bones)
Mesenchyme –> chondroblasts - condrocytes - mineralised scaffold - bone
What is periosteal bone formation
Occurs when periosteum is separated from underlying bone and get formation of new bone
What is Marie’s disease
Periosteal reaction; hypertrophic osteopathy
Get proliferation of new bone along limb bone diaphyses
What would a growth plate look like on X ray if there had been a failure of mineralisation
It would widen; so get a wider radiolucent growth plate
What happens in an angular limb deformity
There is premature growth plate closure due to trauma or infection so get differnetial growth rates of bones e.g radius vs ulna
What does osteopaenia mean
Thinning of bone so reduced radioopacity
[opposite to osteosclerosis]
What is osteoporosis
Deficiency of bone mass due to imbalance between formation and resorption
Get normal bone structure just less of it
- Affects cancellous bone
Bones have thinner trabeculae so are less likely to be able to withstand normal force and can get compression fractures
What is osteomalacia and what are the signs
Softening of bones due to failure of mineralisation
Related to a relative deficiency of phosphorus and/or vitamin D
Get bone resorption and accumulatino of unmineralised osteoid on trabecular surfaces
- Clinical signs: slow onset, shifting lameness, osteophagia, low fertility, hypophosphataemia and anaemia
Why might a dog get osteomalacia
- Low phosphorus from vegetarian diets
- Low vit D with low UV light level or lactation
What is rickets
disease of growing bones where there is failure of mineralisation due to vitD/phosphorus deficiency and physis remains unmineralised and increases in depth
Bones feel thicker because unmineralised osteoid protects the bone ‘beneath’ from actino of osteoclasts so don’t get normal remodelling with age
Clinical rickets signs
Curvature and fracture of bones
Enlarged joints
Abnormal teeth alignment due to failure of jaw growth
Spinal deformities
May have epiphyseal separatino
What is osteodystrophia fibrosa
Extreme form of osteomalacia due to hyperparathyroidism (primary or secondary)
Get bone removal by osteoclasts and replacmeent with fibrous connective tissue
WHat is rubber jaw a sign of
Osteodystrophia fibrosa
Can squeeze canines togehter as jaws have softened
What is nutritional hyperparathyroidism caused by
Excess phosphorus and low calcium/vitD
Classic with just meat/offal diets since these have a high P:Ca ratio
How does a fall in plasma Ca:P ratio affect bone resorption
This fall stimultes release of PTH by parathyroid glands which stimulates osteoclast action
How can renal failure lead to osteodystrophia fibrosa
Via secondary yperparathyroidism
CKD leads to impaired excretion of phosphate so this rises in concentration
And less activated vitamin D gets produed in the kidneys so can’t take as much Ca2+ up from gut
So overal plasma Ca:P falls so get parathyroid gland stimulation to make PTH which activates osteoclasts
Don’t restore balance because normally PTH stimulates phosphate removal from kidney but not possible in chronic renal disease
How does vitamin D poisoning cause osteodytrophy
Get deposition of calcium in the wrong spots including artery walls, alveolar walls, kidney, intestinal mucosa
What diet is vitamin A poisoing associated with
High liver diet (tends to be cats)
What osteodystrophic changes does vitamin A poisoning cause
Promotes osteoblast activity so get more bone deposition so get exostoses i.e new bone formation around joints and foramina from which CNs emerge
Deforming cervical spondylosis
Cartilage damage
OSteoporosis due to stimulating osteoclasts
How does vitamin A deficiency cause osteodystrophy
Abnormalities of modelling membranous bones of skull and get too small skull volume and spinal canal
Because osteoclasts are responsive to vitamin A so in defieicny don’t get enough action
What are the 4 As of fracture fixation
Apposition = presence/size of fracture gap
Alignment = anatomical positioning of fragments relative to each other
Apparatus = type/size/number/position/function of implants
Activity = biological activity of bone
When would you need a load sharing vs load bearing construct
- Load sharing: for when there is anatomic reconstruction so the bones take some of the load
- Load bearing: for when bone isn’t taking load e.g with comminuted fractures and bridging fixation
What three factors must a fracture have to use external coaptation only for management
- Minimally displaced
- Intrinsically stable
- Rapid healing potential
What issues can prolonged use of external coaptation devices cause
Muscle strophy
Contracture; imbalance in tendons in growing animals
How are intramedullary pins useful
Gives excellent resistance to bending
- Not good at resisting other forces
When can we use cerclage wire
To compress fractures circumferentially
Only use on oblique fractures
When to use pin and tension band wiring
For fractures under tension; convert the tensile force to compression force
Used in avulsion fractures
How does a self-tapping screw work
Has a cutting blade on the tip which cuts a thread into the bone so no need to use a tap first
Difference between cortical screws and cancellous screws
Cortical screws have a narrower thread and coarser pitch (more threads)
Cancellous screws have a wider thread and a finer pitch (fewer threads)
What is the difference between placing something as a positional screw vs lag screw
Positional: just cuts thread in near and far cortex but doesn’t pull the two cortices closer together
Lag: overdrill the hole to make a glide hole on the near cortex so when it tightens in to the near cortex, it pulls them closer together
What is a locking screw
Screw with a separate thread on the screw head so it works specifically with a locking plate
How is an interlocking nail useful
Similar to an IM pin; goes down medulla but has holes in it and bolts across to engage with the bone so it can now resist torsion, axial xompression and tensino
What are the three modes a bone plate can be used in
Compression
Neutralisation
Bridging
What do you need for compression plating
Plates with specific holes; compression plates
These holes have a shape that guides the screw head towards the fracture so pulls the ends together
What does neutralisation plating mean
The fracture is first compressed with other implants and then the plate is placed as a load sharing construct
This is useful for oblique/spiral fractures
How does bridging plating work
The bridge is placed to align above and below the comminuted fragment
- This is load bearing so must be very strong
Doesn’t give any compression
Why are locking plates better for bone healing
There is an angle stable construct from locking the screw head into the plate
Therefore don’t need to squeeze onto the bone and doesn’t kill the periosteum as with non-locking
So better fracture biology
What is the minimum number of screws for locking vs non-locking plates
Locking = minimum 4 cortices contained by a screw per fragment; i.e two screws
Non-locking plates = 6 cortices per fragment so 3 screws minimum
What is an arthrodesis
Where bones are made to fuse by debriding away cartilage, packing with bone graft and fixing together
Joint space fills with bone
Difference between direct and indirect reduction
Direct fracture involved manipulation of the fractured ends to reduce the fracture
With indirect reduction, the fragments are manipulated from away from the fracture site itself
Advantages of closed reduction
= not opening fracture site to reduce fracture
Avoids stripping soft tissues from bone so get maintenance of the periosteal blood supply
+ preserves fracture clot
Which bones is it easier to do acloser reduction on
Those where the bone can be seen more easily through the skin e.g tibia/radiu/ulna
Vs femur which is embedded in lots of muscle
How is traction important for indirect reduction
TO straighten the bones
Can suspend the limb with some bodyweight to encourage the msucles to stretch
Which approach to fracture repair would we use if we wanted to achieve anatomical reconstruction and compression
Open reduction with direct technique
What are type 1a/1b/2 linear frames
1a = all half pins
1b = half pins on two aspects with separate connecting bars
2 = at least some full pins through whole bone
When can’t we use type 2 external fixator frames
On humerus and femur due to risk of entering a body cavity; use for distal limb only
What are circular frames useful for
When there is very small amount of space. to put in implants so very thin wires must be used; the circular frame can be used to make the wire very strong
When might we use a freeform external fixator
Mandibular fractures
What type of fractures would we use external fixator frames for
Generally communited fractures since this. isa bridging form of fixation
If we want to reconstruct a fracture should do with internal implants and compression
Autograft
= from the same animal
Allograft
= from same species but different animal
Xenograft
= different species
What are the three functions of bone grafts
Osteoinduction; recruitment of osteogenic cells via cytokines
Osteoconduction: scaffold structure provision for bone to grow onto
Osteogenesis: provision of live cells capable of producing bone
Features of autogenous cancellous bone graft
= harvested from proximal humerus usually using drill and curette
Good at all 3 Os
Features. ofcortical bone fraft
Limited biological property so more for mechanical support
e.g where large osteosarcoma is removed in limb sparing surgery
Features of freeze dried cancellous bone chips as a graft
No cells alive at all so no osteogenesis
Good as a scaffold network (osteoconduction)
Features of demineralised bone matrix as a bone graft
No live cells so no osteogensis
But proteins are exposed for osteoinduction, also scaffold
Features of bone morphogenic protein as bone graft
Powerful osteoinduction!!
Can’t do other Os
= cytokines
Gustilo-anderson classification of open fractures
1 = <1cm wound
2 = >2cm wound but without extensive soft tissue damage
3 = extensive soft tissue damage e.g degloving, avulsions, skin flaps
What should we do if soft tissue closure cannot be achieved
Go for external fixation and then do open wound management
- no point wasting time on internal implants as high chance of infection
When would we swab and culture a fracture wound
Only if infected
Otherwise just culture commensals
Salter harris types 1-5
1 = transverse through growth plate
2 = through growth plate and metaphysis
3 = through growth plate and epiphysis
4 = through growth plate, metaphysis and epiphysis
5 = compression fracture of growth plate
What are the two types of forces that might be acting on growth plates
Pressure
Tension
Knowing which is acting is important for when fixing it
Which bones most commonly get physeal fractures and where on the bone
Femur most common; then humerus, tibia; radius
Much more common in distal physis than proximal physis
What is the preferable internal fixation device for repairing physeal fractures
Smooth K wires
<10% width of the physis
How would we fix an avulsion of the tibial crest and what causes it
Caused due to tension force of the patellar ligament
Fix using pin and tension band wiring to convert tension force to compression
How do. we fix fracture of medial humeral epicondyle
Need alignment and compression
Put epicondyle back in place, use K wires to attach it and then a lag screw
Why might we use a washer before a lag screw when fixing growth plate fractures and when is it especially important
To stop the screw head from counter-sinking into the soft bone
- Especially good for young animals with soft bones
Consequences of physeal trauma
Fracture
Compression esp at distal ulnar physis
Complete closure will shorten bone
Partial closure; asymmetric shortening can cause angular deformity
In the radius and ulna how much do the different growth plates contribute to growth
Radius: 40% from proximal one, 60% from distal
Ulna: 15% from proximal growth plate, 85% from distal one
Why is the distal ulnar physis particularly sensitive to trauma
Because the physis is conical rather than plate
Which dogs is early cessation of ulnar growth normal
Chondrodystrophic breeds eg basset hounds, daschunds
What result comes from early distal ulnar GP cllosure
Radius curvus since radius continues growing which ulna acts as a bowstring
Manifestation = carpal valgus
Which dogs are more prone to traumatising distal ulnar GP
Large breeds
Primary bone tumour types
Osteosarcoma = makes bone
Myeloma, lymphoma and chondrosarcoma don’t
Secondary bone tumour types
Squamous cell carcinoma via local invasion to bone
ANy metastatic tumour
What is the most common canine malignant bone tumour
Osteosarcoma
Accounts for 90% of cases
Which bones are more commonly affected by osteosarcomas
Mostly appendicular skeleton esp distal radius the most, prox humerus prox tibia
24% axial skeleton
Very small amount 1% from soft tissue
Do osteosarcomas cross joint surfaces
No - they stay in original bone
X ray characteristics of osteosarcoma
Mottling of bone structure
Less clear metaphysis
Fuzzy edge of bone with some elevation from bone
Mixture of osteolysis and irregular new bone formation
How do we diagnose an osteosarcoma
This is a histological diagnosis so need biopsy
What are the histological hallmakrs of osteosarcoma
Osteoblasts (oval cells) producing osteoid (pink)
Characteristics of osteosarcoma spread
Highly metastatic; happens early in disease i.e before presentation
Haematogenous spread; first to lungs; then other organs
Less metastatic in cats; less metastatic from axial skeleton
What are the two common tumours of joints in dogs and how is the prognosis different
- Synovial sarcoma; much more favourable prognosis
- Histiocytic sarcoma
What are the 3 major components of fracture assessment
Biological i.e how well will it heal
Mechanical i.e can it be reconstructed vs needing bridging
Clinical factors e.g patient and client compliance and confort level
What is the goal in articular fracture surgery
To slow and minimise degenerative change i.e arthritis progression
What are the principles of articular fracture repair
- Perfect reduction of articular surface
- Rigid internal fixation
- Interfragmentary compression of fracture gap
- Early mobilisation and use of joint
What are avulsion fractures
Where there is detachment of bone fragment at the origin/insertion of a tendon or ligament
Especially happens where arge muscle groups go onto a bone near a weak point
Principle of avulsion fracture repair
Implants must resist the original tensile force
Convert distracting forces into compression using tension band principle
Which side should a plate be places on - tension or compression side?
Tension side
Where do humoral fractures typically occur and how do we manage them
On distal 1/3 of bone
Use plate fixation
DO NOT USE CASTS
Tension side is craniolateral but much easier to fit the plate on the medial surface since this is flatter
Where do radius/ulna fractures typically occur and how can we manage them
At distal diaphyses; esp in toy breeds
Best is plate and screw repair
Could do external fixation
External coaptation could only be used for simple transverse fractures with stability and good aposition
What complication in fracture repair is common in toy breeds and so what approach should we take
Prone to atrophic non-union due to poor fracture biology
Do open fracture reduction and internal fixation
How do we deal with femoral fractures
Go for internal fixation
Tension side is lateral which has good surgical access
Avoid external fixation due to large muscle mass (may have to use if can’t reconstruct fracture)
Where is tension side on humerus, femur, tibia
Humerus = cranial/lateral
Femur = lateral
Tibia = medial
What to remember about presentation of tibial tuberosity avulsion fractures
May present with very mild lameness - need to X ray
How many pins/fragment is mimumum for external skeletal fixator and how thick should the pins be
Minimum 3 pins per fragment, ideally 4
Pins should be 20% bone diameter
Which specific ortho exam test must be done conscious
Patella luxation since grade changes dependent on muscle tone
Which ortho exam tests can only be done on sedated or GA patients
Ortalana test of hip laxity
Barden’s lip lift
Thumb displacement test for hip luxatino
What is an abnormal amount for thumb to lift in barden’s lip lift test
> 5mm; suggests hip laxity
Does a larger or smaller angle of reduction on ortolani test for hip laxity suggest wrose laxity
LArger angle (that legs are abducted before get reduction into place) = more severe
What medium do we use for culturing joint fluid
Bone meat broth
Where do we feel for effusions in stifle
Behind patella lig
Where do we feel for effusions in elbow
Caudlly for bulge between olecranon and lateral epicondyle
Where do we feel for joint effusion at carpus
Cranially; get lack of definition of carpal bones
Where do we feel for effusion at the hock
Cranialy and caudally
What does indirect trauma mean in terms of causing a frature
Wasn’t the actual trauma that caused the fracture but the impact from it
e.g jumping on the floor, getting force travelling up limb and causing fracture at a weak point
Differential diagnoses for swollen painful joint
inflammatory/DJD
Immune-mediated e.g IMPA
Septic arthritis
Neoplastic (chondrosarcoma or histiocytic sarcoma usually)
