Why is repaired tendon said to functionally deficient
Because repair involves fibrosis and the formation of scar tissue. Scar tissue is stronger but stiffer.
Describe the structure of tendon
Triple helix collagen molecule => Collagen fibril => Collagen fibre => Subfascicle => Fascicle => secondary and tertiary fascicles => Tendon unit
- Fibroblasts - withing fascicle. Liealong long axis, make ECM
- Endotenon - Contains blood vessels, nerve, lymph
- Epitenon - Connective tissue that binds fasicles and endotenon together to form tendon
- Paratenon - Aids in gliding mechanism in absence of tendon sheath.Main route for blood vessels
Whats the difference between postional tendons and energy storing tendons
Positional - Anatomically opposing.Transfer muscle force to generate movement at a joint
Energy storing - Store energy from previous stride, then release at recoil. Increasing efficiency of high speed locomotion
What is stress, creep and stress relaxation
Stress - Load experienced by the tendon per unit cross sectional area
Creep - Increased deformation under constant load
Stress relaxation - Load required to cause specific tissue strain decreases with time
Describe indirect fracture healing
Normal process
- When fracture occurs, bleeding causes haematoma formation. GF’s released
- Small amount of bone is resorbed at bone ends & more GF’s released.
- GF’s drive extra osseous blood supply, differentiation, osteogenesis & callus formation
- Remodelling
Fracture => haematoma => granulation tissue => Connective tissue => fibrocartilage & cancellous bone => bone.
Successive cell types require more oxygen. Stages of callus can be skipped if adequate oxygen tension
Describe the 2 Ways of direct fracture healing
Contact healing
- Absolute stability required, NO movement
- Artificially compressed (e.g plate) to <0.01mm
- Direct migration of osteons
Gap healing
- No movement
- <1mm gap
- Lamellar bone forms in fracture gap forming a weak joint.
- Osetons cross fracture gap
What is malunion and what are the 6 types of Non-union
Malunion - Bone unites correctly but in wrong postion
Non union - Failure or delay in bone healing
- Hypertrophic - Callus formed but fracture not healed, inedequate fixation. ( Medullay bone from elsewhere can be placed in gap, allowing increased GF secretions)
- Oligotrophic - Not enough callus
- Dystrophic - No callus
- Nectrotic - Fragment of bone thats been isolated from blood supply (sequestrium)
- Gap - Lost tissue in the middle
- Atrophic - Bone is resorbed. Commonly occurs in radial ulna fractures of toy breeds.
What are the forces acting on a fracture
- Due to the curved shape of diaphyseal bones, Bending loads set up compression on one side and tension on the other
- Shear forces displace fractures perpindicular to long axis, causing over riding
- Twisting loads from muscle contraction => Torsion. These loads are rarely symmetrical, also promoting shear
What treatment would be used for a minimally misaligned fracture
Coaption (cast) - Immobilise fracture
Promblems:
- Can result in furthur malalignment
- Can’t apply to fracture proximal to stifle/elbow
- Cost of frequent redressing can be expensive
What are the 3 surgical methods of fixing a diaphyseal fracture
- External skeletal fixator - Holds bone in place. Allows for secondary bone union (Callus formation), quick and easy to apply, is cheap and adjustable. However pins can loosen
- Plate - Allows secondary or primary bone union. Can apply compression, neutralisation or butress. Achieve perfect reduction and is minimally invasive. However requires large skill set and equipment set
- Interlocking nails - Intramedullary pin which is fenetrated to allow the nails to lock into cortical bone. Strong and used for comminuted fractures.
What Complimentary prostesis can be used
- Lag screw - At right angle to fracture line
- Cerclage wire - For long oblique fractures. Can disturb extra osseues blood supply
- Intramedullary pin - Resists shear force. Must combine with another method for resistance to compression & torsion
What are the 4 A’s when evaluating fractures
- Alignment (of whole bone)
- Apposition (how fracture is alligned)
- Apparatus
- Activity
What attaches to the extensor process of the distal phalanx
- In the hindlimb, Long digital extensor
- In the forlimb, Common digital extensor
How does the hoof grow
Throughout life, Growth occurs from the coronary corium where germinal cells produce keratinocytes
how does laminitis occur
Arteriovenous anastomoses usually closed under normal circumstances. However when its open, allows blood to bypass capillary network & into dermis & causes ishaemia
Describe the 4 diagnostic nerve blocks of the equine limb
- Low palmer digital block - Anaesthetises navicular bone and distal phalanx. Insert between lateral cartilages.
- Mid pastern palmer digital block - Anaesthetises Navicular bursa, distal phalanx, distal interphalangeal joint. Needle inserted under tightened ergot ligament
- Abaxial sesamoid block - Anaesthetises proximal interphalangeal joint, distal sesamoid ligament and lamellar corium. Palpate palmar digital nerves on abaxial surface of proximal sesamoid
- Low palmar block - Anaesthetises metacarpophalangeal joint & proximal sesamoid. Groove between interosseus muscle and flexor tendons
How would you diagnose lameness in the forlimb and hindlimb
Forelimb
During weight bearing on the lame limb, the head will lift to try eleviate the weight of the limb and dip on the normal limb so it bears the weight of the head and neck
Hindlimb
Greater degree of difference between maximal and minumum pelvic heights during the stride of the lame limb
Label the ultrasound of the equine distal limb (transverse)
- Super digital flexor tendon
- Deep digital flexor tendon
- Check ligament (inferior)
- Suspensory ligament
- Metacarpal bone (third)
B - Tendon sheath
What are the direct and indirect costs of lameness
Direct
- Veterinary treatment
- Drugs
- Reduced milk yield
- Herd persons time wasted
- Milk wasted due to withholding time of medicines
Indirect
- Reduced fertility
- Increased rate of culling
Describe the lameness scoring test for cows
- Score 1 - Flat back when walking and standing. normal
- Score 2 - Stands with a flat back, arch in back when walking
- Score 3 - Back arch when standing and walking. shortening of stride
- Score 4 - Partially weight bearing on affected limb
- Score 5 - Affected limb wont bear weight. Reluctant to move
Whats the difference between prevelance and incidence
Incidence - The number of cases over a given period of time (36/100 cows were lame this year)
Prevelance - The amount of cases on a given day ( 36/100 cows are lame today)
What management factor can affect the prevelance of laminitis
Housing
Needs sufficient space to lay down and ruminate for 11-14 hours. if insufficient time is spent ruminating, decrease in bicarbonate causing ruminal acidosis. This causes laminitis due to poor quality horn and inflammation of laminae
Feed
TMR must be sufficiently mixed, otherwise cows will pick out more palatable feed leaving roughage. Decrease in bicarbonate.
What control measures should be taken to reduce lameness in cattle
- Foot bath schedule
- Routine trimming
- Immediate treatment of clinical cases
- Keep accurate records
Describe the sructure of intervertebral disk
- Nucleus puloposus - Contained under pressure inside
- Annulus fibrosus - Encircling bundles of fibrocartilage
