Introduction to juvenile osteochondral conditions

Question 1

Disease processes

Answer 1

1. osteochondrosis (OC)
   - development disease
   - due to failure of endochondral ossification
   - subdivided into 2 conditions (i) osteochondritis dissecans (OCD), (ii) subchondral cystic lesions (SCL)
2. osteochondral fragmentation (OCF)
   - traumatic dz

Question 2

Pathogenesis of osteochondrosis

Answer 2

• focal failure of endochondral ossification at epiphyseal growth cartilage
• follows trauma to microvasculature
• strong location predispositions
  — lateral trochlear ridge of the stifle is the most common place for OCD to happen in horses
  — OCD happens because of sliding forces (they cause shearing and a fissure formation)
  — medial femoral condyle -> lots of crushing forces which cause collapse of the thickened cartilage, avascular necrosis -> bone cyst
• lesions form during periods of fast growth
  — all lesions originate <2y/o
• dynamic process in <8m/o, lesions may heal
• multifactorial
  — polygenetic heritable dz
  — overnutrition
  — rapid growth
  — mineral imbalances
  — copper deficiency has been shown to predispose to osteochondrosis

Question 3

When the lesion remains as osteochondrosis what does it look like radiographically?

Answer 3

• thickened necrotic cartilage & subchondral bone

Question 4

When OC lesion progresses to OCD what happens?

Answer 4

• fissure appears in the thickened cartilage
• mineralisation occurs within the lesion
• sometimes break free
  — fragmentation

Question 5

When OC lesion progresses to subchondral cystic lesion what happens?

Answer 5

• crushing of the cartilage -> avascular necrosis
• necrosis of the thickened cartilage
• cyst has an inflammatory lining so is self-propagating

Question 6

Osteochondrosis vs osteochondral fragmentation

Answer 6

Age lesions develop
- OC: <2y
- OCF: any age

When CS occur
- OC: immediately OR when horse begins work OR never
- OCF: immediately OR never

Breed
- OC: TB, WBs
- OCF: any athlete

Sex
- OC: none
- OCF: none

Question 7

Clinical presentation

Answer 7

Varying degree of
- joint effusion
- lameness
- heat

Positive to joint flexion

Inflammation due to synovitis & osteitis
- cartilage has no nerves

Often no CS
- lesions detected on pre-sales rads

Question 8

Diagnosis

Answer 8

• hx
• palpation
• lameness assessment
• regional anaesthesia
• rads
• US
• MRI
• CT
• nuclear scintigraphy

Question 9

How to interpret radiographic lesion

Answer 9

1. radiographic description
   - number
   - size
   - shape (round/triangular/irregular/coallescing
   - opacity (radiolucent/radiodense/heterogenous
   - location
   (don’t forget soft tissue)
2. make an assessment of pathology
   - lysis / sclerosis / new bone formation
3. diagnosis

Question 10

Challenges related to diagnosis

Answer 10

• experience of O
• O expectations/purpose of horse
• lesions often silent until significant increase in exercise regime
• horses from different disciplines will start at a different age
• temperament may not be amenable to all diagnostic steps
• some lesions may be cartilaginous only so not visible on some radiographs
• it is possible for lesions to heal

Question 11

Tx & management

Answer 11

Conservative
- no tx

Medical
- intra-articular meds

Surgical
- arthroscopic fragment removal
- debridement of diseased cartilage & necrotic subchondral bone
- other proceudres

Euthanasia

General rule of thumb
- loose fragments in joint (OCD & OCF) -> arthroscopic removal
- thickened cartilage (OC) -> can monitor and see
- subchondral cystic lesions -> more complicated