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Joints Degenerative - Pathology (view source)

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===Degenerative joint disease (DJD)===
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[[Image:DJD horse.jpg|right|thumb|100px|<small><center>DJD in a horse (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*'''Osteoarthritis, osteoarthrosis'''
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*Due to acceleration of normal ageing process - wear and tear
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*Destructive disease leading to:
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**Loss of weight-bearing [[Joints - normal#Articular cartilage|articular cartilage]]
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**Erosion, fibrillation of cartilage
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***Clefts in the cartilage, perpendicular to the surface
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**Complete exposure of underlying bone
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***Bone appears polishes, dense - [[Musculoskeletal terminology|eburnation]]
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***Radiographically - joint space reduction due to loss of cartilage
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**[[Musculoskeletal terminology|Osteophyte]] formation at joint margins
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**Remodelling of adjacent bone
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**Brown/yellow discolouration
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**Synovial hypertrophy
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**Capsular fibrosis
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*May affect one or multiple joints
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*May or may not be symptomatic
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*Pathogenesis:
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**Not entirely clear but linked to loss of [[Joints - normal#Articular cartilage|proteoglycans]] and subsequent lubrication
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**Increased water content due to improper binding -> softening of cartilage = chondromalacia
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*Predisposing factors:
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**Persistent trauma
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**Joint instability / dysplasia
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***[[Joints Degenerative - Pathology#Luxations and subluxations|Luxations and subluxations]]
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***[[Joints Developmental - Pathology#Hip dysplasia|Hip dysplasia]]
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***[[Joints Developmental - Pathology#Elbow dysplasia|Elbow dysplasia]]
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**Conformational abnormalities / congenital malformations
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**[[Joints Developmental - Pathology#Osteochondrosis|Osteochondrosis dissecans]]
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**Intra-articular fractures
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**[[Joints - degenerative#Calve Legg-Perthe's disease|Calve Legg-Perthe's disease]]
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===Luxations and subluxations===
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====Patellar====
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*In stifle joints of dogs and horses
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*Possibly inherited
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*'''Small''' dog breeds:
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**'''Medial''' luxation
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**Due to underdevelopment of medial femoral condyle
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*'''Large''' dog breeds and '''horses''':
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**'''Lateral''' luxation
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====Atlantoaxial====
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*In dogs, calves, horses and goats
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*Miniature dog breeds:
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**Failure of fusion of odontoid process to rest of axis
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*Calves:
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**Aplasia or hypoplasia of odontoid process
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====Temporomandibular====
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*In dogs, particularly Basset Hounds, Irish Setters
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*Normal movement of mandibular coronoid process is interfered with by zygomatic arch
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*Happens on one side -> open jaw locking
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===Calve Legg-Perthe's disease===
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*Almost exlusively in small dogs, particularly terriers and poodles
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*Clinical signs appear at age of 4-11 months
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*Grossly:
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**[[Bones Degenerative - Pathology#Osteosis|Aseptic ischaemic necrosis]] in central parts of femoral head
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***Possibly due to occlusion of blood vessels
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**Fragmentation of [[Bones - normal#Bone organisation|trabecular bone]]
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**Collapse of femoral head
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**Revascularisation of femoral head
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**Formation of new bone and [[Musculoskeletal terminology|osteophyte]] formation around femoral head and acetabular rim prior to old bone reabsorption
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**-> severe degenerative arthropathy
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===Degenerative arthropathy===
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*In older dogs (8+ years)
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*Occurs bilaterally
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*In shoulders
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*?Due to gradual atrophy of muscles with age -> joint laxity
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===Traumatic injuries===
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*Sudden
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*Varying severity
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*Acute injuries:
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**Sprains
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***Minor - resolved without any consequences
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***More severe may result in persistent capsular and ligament laxity -> degenerative arthrosis -> impaired function
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**Subluxations
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**Luxations
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**Intra-articular fractures
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***[[Bones Fractures - Pathology#Fracture repair|Fracture healing]] may cause discontinuity of the articular surfaces
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**Puncture wounds to foot may allow infection to travel to [[Joints - inflammatory|joints]], bursae and tendon sheaths
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**Haemorrhage into joint
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***May occur in animals with clotting defects without special trauma
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****Usually polyaricular
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****Recurrent
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****May cause pitting of articular surfaces -> degenerative arthrosis
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===Nutritional diseases===
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====Hypervitaminosis A====
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*See [[Bones Metabolic - Pathology#Hypervitaminosis A|metabolic diseases of bones]]
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*May cause spondylosis of cervical vertebrae
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*Mainly on dorsolateral surface
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*Also in elbow and shoulder joints -> fixation of joint
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*May resolve with changes of diet
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===Disc protrusion===
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[[Image:Intervertebral disc degeneration.jpg|right|thumb|100px|<small><center>Intervertebral disc degeneration (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*Occurs mainly in dogs
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*Almost always '''dorsal''' protrusion due to eccentric position of [[Joints - normal#Fibrocartilagenous joints|''nucleus pulposus'']]
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*Main sites are '''cervical and lumbar''' regions
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**Thoracic vertebrae have [[Joints - normal#Fibrocartilagenous joints|conjugal ligaments]]
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*Degeneration precedes protrusion (two patterns):
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**'''Chondroid'''
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***In chondrodystrophic breeds
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***Concurrent calcification of [[Intervertebral disc degeneration|degenerated ''nucleus pulposus'']]
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***Progressive loosening and fragmentation of overlying ''annulus fibrosis'' fibres
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****Damaged by both compressive and rotational forces
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***Predisposing degeneration of the discs occurs by one year of age in most of the dogs
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***Protrusion usually occurs in males, 3-6 years of age
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***'''Sudden complete protrusion''' -> severe damage to spinal cord in the area
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***Widespread necrosis and haemorrhage
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***Extruded material is gritty, hemorrhagic or “cheesy”
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**'''Fibroid'''
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***In non-chondrodystrophic breeds, horses, pigs
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***Usually occurs later in life
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***Pathogenesis:
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****Progressive dehydration and collagenisation of ''nucleus pulposus''
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****Fraying and fragmentation of lamellar ''annulus fibrosis'' fibres
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**** -> Attempts to repair by fibrosis
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**** -> Weak area in the annulus
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**** -> '''Partial protrusion''' (rarely may calcify) of nucleus into spinal canal
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*****May be dorsal or lateral
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**** -> Pressure on spinal cord
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**** -> Demyelination of white matter
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**** -> Progressive weakness of structures innervated distally to the lesion
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***Disk material may enter blood vessels causing fibrocartilagenous embolism
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****May present without any disk symptoms
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*'''Sudden protrusion''' can occur in any breed due to traumatic compression of spinal cord
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===Cervical spinal stenosis===
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*Usually funnel-shaped
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*Stenosis in dorso-ventral plane
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*May occur at more than one site
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*Predisposed in some breeds: Great Dane, Doberman, Basset Hound, Irish Wolfhound, Old English Sheepdog
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*Clinical signs: cervical pain -> ataxia -> quadriplegia
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===Cervicospinal arthropathy===
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* = "'''Wobbler'''" in horses
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*Usually presents in first two years of life
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*Mainly in fast growing thouroughbreds
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*Most common site is C3-C4, can occur anywhere
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*Abnormal laxity between the vertebrae + cervical vertebral malformation may be evident
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*[[Musculoskeletal terminology|Osteophyte formation]] at edges of synovial components of joint
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*Some due to stenosis of neural canal later in life (1-4 years of age)
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*Clinical signs:
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**Ataxia - hindlimbs more affected
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*Presumed cause is rapid growth
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===Spondylosis===
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[[Image:Spondylosis.jpg|right|thumb|100px|<small><center>Spondylosis (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*Often in bulls and dogs, occurs also in horses, cats and pigs
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*[[Musculoskeletal terminology|Osteophyte]] formation on ventral aspect of vertebrae
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**Often around lumbar region
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**Adjacent to intervertebral spaces
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**Varies in size - small spurs -> 'bridges' between vertebrae
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**May extend over few vertebrae
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*Pathogenesis:
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**Repeated abnormal movement between joints -> stress
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** -> Degeneration of [[Joints - normal#Fibrocartilagenous joints|''annulus fibrosis'']]
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** -> [[Musculoskeletal terminology|Osteophyte]] formation
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*In dogs usually no symptoms
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*In bulls may cause inability to mount
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*In severe cases repeated damage may progress to recurrent posterior weakness and ataxia in conjuction with fractures of spondylitic and vertebral bone
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===Cranial cruciate ligament rupture===
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*Autoantibodies against collagens seen in the joint fluid – no relationship to the disease (ie: not an autoimmune disease) – can be seen in any joint disease
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===Steroid arthropathy===
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*From glucocorticoids injected into joint as antiinflammatories
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*Injection sometimes causes rapid progression of degeneration
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*Glucocortyicois suppress anabolic effect of chondrocytes -> reduction of cartilage matrix syhthesis -> proteoglycan depletion -> slower repair
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