Equine Tendon Healing Flashcards
I have wings and I have a tail, across the sky is where I sail. Yet I have no eyes, ears or mouth, and I bob randomly from north to south. What am I?
A kite
Label tendons of distal equine limb?
What is the structural hiearchy of tendon and ligament?
Describe the normal ultrasonographic appearance of the metacarpal SDFT and DDFT?
Describe the normal ultrasonographic appearance of the palmar pastern?
What is the function of the SDFT?
- Function
- To support the MCP joint
- Elastic energy store for energy
- efficient locomotion
- (to flex the digit –max muscle contraction only 2mm)
- Loaded early in the stride
- Subject to very high
- Stress (1 tonne peak load; 1cm 2 CSA
- Strain –16% at gallop ( in vitro rupture 12-20%)
- Strain rate –200%/sec
Discuss superficial digital flexor tendonitis?
- Among the most common musculoskeletal injuries suffered by Thoroughbred racehorses
- Each training season 10-15% National Hunt and Flat racehorses affected
- Also common in event horses and showjumpers
- Frequently career ending (particularly racehorses)
How can SDFT tendonitis be diagnosed?
Diagnosis
Observe
- Characteristic palmar bow
Palpate
- weight-bearing
- limb lifted
Assess
- BOTH LIMBS
- Heat
- Pain on palpation
- Suppleness of tendons
- Size of tendon
- Peritendonous oedema
What is the role of diagnostic ultrasonography?
Role:
- Diagnosis
- Both limbs
- Echogenicity
- core lesion
- CSA
- Fibre alignment
- Assessment of severity
- ~7 days after injury
- Prognosis
- initial severity
- fibre alignment pattern when returns to full work
What can be seen here?
typical core lesion (hypo/anechoic regiion in centre of tendon)
What is the consequence of tendon injury?
- Tendon heals (fibroses) after injury but does not regenerate
- Healed tendon is stiffer as a structure compared to normal tendon
- Re-injury common
- 56% for NH horses (Dyson, 2004)
- Less efficient energy-store
- poorer performance
- Re-injury common
- Aim of treatment should be regeneration
How does tendon adadption work?
- Load induces matrix deformation
- Tenocytes are able to detect this and through mechanotransduction a cellular response in seen
- This enables remodelling of the tendon matrix according to imposed loads
- The result is tendon adaptation
What are Matrix Metalloproteinases?
- Tightly regulated group of proteinase enzymes able to degrade tendon matrix
- Specific MMPs are able to degrade different components of the matrix
- Activity regulated by
- tissue inhibitors of metalloproteinases (TIMPs)
- whether the molecules are in their active form (zymogens)
- their location within the matrix
- Crucial for normal matrix turn-over and repair
How does the immature tendon adapt?
Immature tendon adapts to strains levels and exercise as a juvenile
- Tendon optimised as a ‘ spring ’
- Increased matrix -> stiffer -> less efficient energy store
- Decreased matrix -> more elastic -> less efficient energy store
- Tendon at skeletal maturity sufficient to withstand normal athletic endeavour
- Sufficient for escaping from predators
Why do tendons fail?
- Degeneration precedes injury
- Tendon operating close to its functional limit –low tolerance
- Degeneration in matrix / structural properties dramatically increase risk of tendinopathy
- Tendon ageing!
What is tendon degeneration?
- Accumulation of microdamage which occurs in the central region of the SDFT
- Gross mechanical properties of tendon unaffected
- If not repaired by tenocytes >> accumulation results in clinical injury
Outline the stages of tendon damage?
Stage I
- Tendon matrix degradation
- Cumulative -‘ageing’
Stage II
- Fibrillar slippage n breakage of cross-links
Stage III
- Fibril rupture
Stage IV
- Complete rupture
Draw a schematic why tendons fail?
What are the mechanisms of tendon inflammation and degeneration/cumulative fatigue damage?
- Exercise
- High number of loading cycles
- Faster gaits
- Physical disruption
How do abnormal loading events occur?
- Muscle fatigue >> inco-ordination and abnormal loading
- Fast twitch DDF muscle fatigues earlier >> reduced metacarpophalangeal stabilisation>> abnormal SDFT loading
- Increased risk of tendon injury at end of race
After skeletal maturity tendon loses its ability to adapt –why??
- Aged tenocytes have reduced anabolism
- Aged tendon has reduced numbers of tenocytes and intercellular communication
- reduced co-ordinated response to load
How does exercise effect the tendon?
- Exercise
- Energy loss through hysteresis
- Results in rise in tendon core temperature up to 45ºC
- Although tenocytes appear relatively “heat resistant”, high Tº >> increased cytokine production
- Altered physicochemical environment
What happens at a cellular level during tendon inflammation?
- The loss of ultimate tensile strength induced by cyclical loading is dependent on the presence of live cells
- Tissue culture media from cyclically loaded explants have elevated levels of both active and proMMP-2
- Inhibition of MMP activity prevents loss of UTS
Discuss crimp?
- Tendons should have crimp
- IN FIRST PHASE OF LOADING CRIMPING STRETCHES OUT
- In older horse they loose that crimp which moves the stress at which they rupture to the left
Look at a change in crimp with age?
Discuss COMP?
Cartilage oligomeric matrix protein (COMP)
- Large pentameric glycoprotein
- In all ‘ loaded ’ tissues –tendon, ligament, cartilage, meniscus, intervertebral disc
- COMP accelerates collagen fibril formation
- Organisational molecule
- Correlates with mechanical strength at skeletal maturity –high COMP = high strength
Discuss COMP variation with age and tendon type and site?
What is the proposed mechanism for ST ageing?
In tendon injury what can be seen in the acute inflammatory phase (days)?
Clinical signs
- Lameness
- Pain on palpation
- Heat
- Swelling
Pathology
- Haemorrhage
- Inflammation
- neutrophils
- macrophages and monocytes
- increased blood flow
- oedema
- proteolytic enzymes
In tendon injury what can be seen in the subacute reparative phase (weeks)?
Clinical signs
- Reduction or absence of lameness
- Resolution of signs of inflammation
- Tendon still palpably enlarged and soft
- Signs of re-injury if exercised too early
Pathology
- Angiogenesis
- Fibroplasia
- ++ fibroblasts
- collagen III
- small collagen fibrils formed
In tendon injury what can be seen in the chronic remodelling phase (months)?
Clinical signs
- Tendon size decreases
- Tendon less pliable
- Reduced fetlock extension
- (Contractures)
Pathology
- Collagen transformation from III to I
- Cross-linking
- Thicker collagen fibrils
How should the acute inflammatory phase of tendon injury be treated?
Acute phase; anti-inflammatory
Physical therapy
- application of cold
- compression bandage
- MCP joint support
- rest
Medical treatments
- NSAID’s
- Corticosteroids (early)
How should the subacute phase of tendon injury be treated?
Subacute phase - fibroplasia
Mobilisation
- early
- progressive
Regular ultrasonographic monitoring
- CSA’s
How does chronic phase remodelling look like?
What are some treatments for tendonitis?
- Stem cells (best evidence rate behind it for reducing reinjury but reinjury rates are still high)
- Bone marrow aspirate concentrate
What is the role of stem cells in treating tendonitis?
REGENERATION versus REPAIR
Treatment should be aimed at:
- Making more functional scar tissue
- Reforming tendon matrix
Intralesional treatment needs to be within month of injury as past this the tendon is just full of fibrous tissue
Discuss stem cell therapy?
- Supporting experimental data in vitro and vivo
- Mechanism of beneficial effect uncertain – synthesis of matrix or orchestration of healing??
- Cell survival appears to be transient
- Recent clinical case series supportive of beneficial effects
How can prevention or reinjury of the tendon be achieved?
Surgery Desmotomy of the ALSDFT
- ? higher incidence of suspensory desmitis
Prognosis
- Potential for reduced rate of re-injury
How can a support boot be used to prevent reinjury?
Prevention is better than cure. What methods are there for prevention of tendonitis?
- Maximise the quality of the tendon prior to skeletal maturity
- Reduce degeneration after skeletal maturity
- Reduce risk factors for tendonitis
- (Early detection)
Discuss the window of opportunity for maximising tendon prior to skeletal maturity?
Can’t improve on pasture exercise in the young animal
Look at the effect of early tendon conditioning?
Summarise recommendations for ‘ tendon training’?
- Pasture exercise vital for tendon development
- ?Low numbers of high load cycles
- ?Extra exercise beneficial but tendon also easily injured
- Different tissues most sensitive to exercise at different ages
- ?tendon/ligament (?and cartilage) most responsive prior to yearling stage
- ?bone most responsive at yearling stage
- In adult, training has no effect on tendon but induces degeneration
- adult training only for cardiovascular (?and respiratory) systems, bone and muscle
How can you reduce tendon degeneration in the adult?
Prevent cumulative matrix damage
- reduce number of damaging loading cycles
Take home message
- avoid ‘tendon’ training in the adult
What are the risk factors related to tendon injury?
Related to high impact on tendon
- Speed
- ground surface
- Inco-ordination
- fatigue
- Jumping
- Weight
- Shoeing
What may be used for early detection of tendonitis?
Molecular Markers
- Potentially a more sensitive screening tool for detecting subclinical injury
- Lots of markers looked at but none yet sufficiently accurate
- Ongoing area of research
