CH73- OCD

Question 1

• What is osteochondrosis, and where are the commonly accepted locations in the dog??

Answer 1

• Disorder of endochondral ossification
• Endochondral ossification is the development of bone through the the cartilage in the epiphysis and physis undergoing mineralization

Question 2

• Where are the commonly accepted locations in the dog?

Answer 2

• Humeral head - caudocentral or caudomedial
• Medial aspect of humeral condyle
• Lateral or medial femoral condyle
• Medial or lateral trochlear ridge of talus

Question 3

• What is OC latens

Answer 3

• Early, microscopic dz

Question 4

• OC manifestans?

Answer 4

• Subclinical lesion, macroscopically/radiologically apparent

Question 5

• OC dissecans?

Answer 5

• Attached or loose cartilage flaps w/clinical signs

Question 6

• What is the sex predilection for OCD lesions?

Answer 6

• Male >female unless talus

Question 7

• Describe the process of long bone development.

Answer 7

• MSCs congregate —> Turn into chondrocytes and form cartilage bone models
• Cartilage bone models form and elongate through growth centers in the epiphysis (secondary) & diaphysis (primary), & growth plates
• Cartilage converted into bone via EO

Question 8

• What is being shown in these images?

Answer 8

• The first image shows the growth plate and it’s relationship to the epiphysis
• The second image shows the epiphysis in relation to the developing articular cartilage
• [Image in source document]

Question 9

• What % of length to bones do GPs contribute? Epiphyseal centers?

Answer 9

• 70-85% - GP
• 20-25% - epiphyseal centers

Question 10

• When does most bone development occur?

Answer 10

• 12-26 weeks

Question 11

• What is the hueteer-Volkmann law?

Answer 11

• Growth is slowed by increased mechanical compression and accelerated by reduced loading → growth is not continuous ie saltation, and stasis

Question 12

• What constrains the circumference of the growth plate?

Answer 12

• Ring of LaCroix

Question 13

• Name the zones of the physis? Which is the only vascular zone?

Answer 13

Ross Palmer Helped Me

Resting zone
* juxtaposed to epiphysis and penetrated by chondro-epiphyseal blood vessels;
* only vascularized portion of growth plate- here stem cells scattered throughout, divide at slow rate , daughter cells start columns that originate proliferative zone

Proliferative zone
* Chondrocytes are thin, flat; arranged in columns, divide/enlarge slowly, synthesize matrix

Hypertrophic zone
* Columnar organization; rapidly enlarge, continue to make matrix

Mineralization zone
* Chondrocytes obtained final size/shape, newly formed matrix mineralizes and chondrocytes die abruptly by apoptosis

Question 14

• What occurs at the junction of the growth plate and metaphysis to complete conversion of cartilage into new metaphyseal bone?

Answer 14

• Endochondral ossification

Question 15

• Describe the process of endochondral ossification.

Answer 15

• Conversion of cartilage into bone (metaphyseal region)
• Mineralization zone → chondrocyte undergo terminal differentiation and secrete specialized matrix that calcifies
• Chondrocytes die and clasts come in and remove them leaving lacunae
• Vasculature from the metaphysis invade the lacunae and bring MSCs (controlled by VEGF)
• MSCs become blasts and lay down woven bone on the calcified cartilage → primary spongiosa
• Woven bone and calcified cartilage replaced by lamellar bone → secondary spongiosa

Question 16

• What are the two layers of the articular-epiphyseal complex?

Answer 16

1) Thin outer layer → immature articular cartilage
• Does not participate in EO

2) Thick inner layer → secondary center of ossification
• Similar to GP w/ different architecture
• Responsible for enlargement of the epiphysis by cartilage formation and mineralization
• Has abundance of blood vessels → cartilage canal vessels

Question 17

• What are the layers of the thin outer layers of articular -epiphyseal junction of developing bones? (articular cartilage)

Answer 17

So That Ross (too) Cool

• Superficial zone
• Transitional zone
• Radial zone (uncalcified)
• Tide Mark
• Zone of calcified cartilage

Tide mark = separation from uncalcified radial zone and calcified zone; completion of maturation process

Question 18

• What is chondrification?

Answer 18

• As the mineralization in the center of the epiphysis reaches the outer articular cartilage the vessels in the cartilage canals regress

Question 19

• How does growth plate expansion occur?

Answer 19

• Formation of new cartilage at the GP pushes the epiphyseal articular complex away from the metaphysis
• Cartilage becomes bone at the junction between the metaphysis and the GP

Question 20

• Where does mineralization take place in the epiphysis?

Answer 20

• In the center → chondrocytes in the center are larger and surrounded by matrix
• Most cell proliferation takes place on the periphery

Question 21

• What is the blood supply to the chondro-epiphysis (of articular cartilage) and how is this different compared to the growth plate (proliferative, hypertrophic, and mineralization zones?)

Answer 21

• Abundant vasculature → chondro-epiphyseal blood vessels originate from perichondral plexus and course through cartilage canals → at termination have afferent arterioles and returning venules forming glomeruli

Question 22

• What is associated with development of OCD?

Answer 22

• Heritability 10-45%; Polygenic trait
• Rapid growth
• Overfeeding
• Elevated GH/IGF-1/T3/T4/insulin
• Diet (NO correlation between diet and OC)
• Anatomic features of joints
  =Elbow dysplasia
  =Hyperextension of tarsus
  =Relatively long ulna
• Biomechanical overload on joint surfaces (not confirmed)
• Macrotrauma
  =may convert OC manifesta → OCD; Not reported in dogs
• Microtrauma
  =Disruption of chondro-osseous cartilage canal vessels
• Exercise

Question 23

• What are 2 types of OC lesions that affect the Articular Epiphyseal Complex (Olsson)?

Answer 23

• Type 1= Center of affected articular surface without vascular attachments (caudal humeral head; lateral femoral condyle)
• Type 2= joint margin w/vascular attachment (ie talus, or fcp @ joint margin)

Question 24

• What is the theory of the pathogenesis of focal OC of articular cartilage?

Answer 24

Theory 1 (proven in pigs and humans)
* Vascular trauma occurs causing a focal area of necrotic bone or epiphyseal cartilage which ultimately leads to necrosis of the overlying cartilage

Theory 2
* Damage to the blood vessels during the stage when the vessels that originate from the perichondrium are being replaced by vessels from adjacent bone marrow
* Damage to the blood vessels causes infarcted cartilage
* Infarcted cartilage does not mineralize → prevention of EO
* Cartilage around it continues to develop → thickened cartilage in that area
* The neighboring subchondral bone becomes reactive and inflamed → OC latens
* Thickened cartilage degenerates → OC manifesta
* The necrotic cartilage can go two ways:
* Heal → Organized and heal through granulation tissue and intramembranous ossification
* Propagate and extend to the joint surface and break off overlying cartilage → OCD

Question 25

* What is the proposed pathogenesis of physeal OC?

Answer 25

* **Disruption to the vessels in the resting zone** of physis will cause an area of focal necrosis * With lengthening the focal area will reach the metaphyseal side at mineralization zone * That area will resist vascular invasion and therefore will not mineralize → **retained cartilage core**

Question 26

* What are the two types of growth plate OC?

Answer 26

* Retained cartilage core, UAP

Question 27

• What is the consequence of growth plate OC in the ulna?

Answer 27

• Can be incidental or can cause growth abnormality • Can cause premature closure of physis - radial bowing, shortened ulna, valgus deformity

Question 28

• What patients is conservative management appropriate for regarding OCD?

Answer 28

• Small subchondral lesions, • mild lameness, • no joint mice or its retained in area that is unimportant; • <6.5 mo of age • Or endstage - ie, talus w/OCD that already has secondary OA

Question 29

• What does conservative management consist of?

Answer 29

• Weight and caloric intake management • NSAIDs • Supplements • Activity restriction

Question 30

• What are 2 categories of treatment for OCD lesions?

Answer 30

• reparative/palliative • restorative

Question 31

• What are 5 types of palliative/reparative treatment for OCD lesions?

Answer 31

• Curettage - removal of necrotic cartilage and subchondral bone - expose bleeding subchondral bone • Spongilization - exposing the underlying cancellous bone beneath the subchondral bone (spongiosa) • Abrasion arthroplasty - grind down the underlying bone to expose vascular tufts from the marrow • Forage - multiple holes drilled with k-wire or microdrill burr • Microfracture - subchondral bone pierced with picks or awls

Question 32

• What type of cartilage edge inhibits fibrocartilaginous filling of the defect?

Answer 32

• Beveled • Edges should be squared!!!

Question 33

* What are the 4 grades of OC in the prox humerus?

Answer 33

Grade 1 = Cartilage surface normal; cartilage slightly thickened; “minuscule” subchondral defect Grade 2= Cartilage surface mottled; cartilage more thickened; small cleft between cartilage and subchondral bone Grade 3= Discoid elevation of cartilage surface; large cleft; underlying sclerotic subchondral bone Grade 4= Typical partially detached cartilage flap or separated flap and joint mice

Question 34

• What is the difference between spongialization and curettage?

Answer 34

• Spongialization - complete debridement of subchondral bone plate under the cartilage lesion to expose underlying cancellous bone ie spongiosa • Curettage - debriding flap of cartilage and necrotic bone down to subchondral bone

Question 35

• What should be avoided in curettage and why?

Answer 35

• Avoid debriding past the subchondral bone plate → results in resorption and fibrous repair • Maintaining the subchondral bone plate results in more congruency in the joint

Question 36

• When is curettage contraindicated?

Answer 36

• If there is preexisting fibrocartilage

Question 37

• What is abrasion arthroplasty indicated for?

Answer 37

• Eburnated subchondral bone in order to expose healthy underlying bone and vascular tufts from the marrow cavity

Question 38

• What is the difference between forage and microfracture?

Answer 38

• Forage - drill numbers holes in subchondral bone w/microdrill vs k-wire; often if bone is eburnated or sclerosed (less damage to subchondral bone plate) • Microfracture - after removal of cartilage, subchondral bone pierced with picks or awls, often done with scope

Question 39

• What is a reported downside to microfracture?

Answer 39

• May compact bone around holes and seal off viable bone marrow which may inhibit repair

Question 40

* What is being performed?

Answer 40

* Microfracture with an awl

Question 41

• What are 3 restorative techniques in the treatment of OCD?

Answer 41

• Reattachment of cartilaginous and osteochondral fragments • Osteochondral transplant • Synthetic resurfacing • Implantation of cells/tissues/synthetic materials

Question 42

• What makes fragment reattachment often not feasible in dogs?

Answer 42

• Size of defect often too small

Question 43

• What osteochondral transplant technique improves contour of defect and addresses tissue scarcity problem?

Answer 43

• Mosaicplasty → taking many smaller grafts to fill large defects

Question 44

• What joints has OATS procedure been described in?

Answer 44

• Stifle • Humerus • elbow

Question 45

* What are 3 common donor sites for grafts?

Answer 45

* Medial sulcus terminalis (stifle) * Medial or lateral trochlear ridge (proximal)

Question 46

• What are 3 disadvantages to an osteochondral autogenous graft?

Answer 46

• Donor site morbidity→ donor site fills with fibrocartilage → inflammation → joint degeneration • Difference in graft thickness/biomechanical ability • Inferior quality if taken from diseased joint

Question 47

• What are the outcomes of OAT in the stifle joint? Shoulder joint?

Answer 47

• Stifle → 20% resolution of lameness at 6-15 mo • Shoulder → 80% resolution at 3-18 weeks

Question 48

• What materials is the bilayered synthetic osteochondral resurfacing implant made of?

Answer 48

• Textured titanium base → in and on growth • Polycarbonate-urethane plug surface • =synacart (Arthrex)