Osteochondrosis Flashcards
What are the different classifications of osteochondrosis based on disease stage?
- Osteochondrosis latens: early microscopic disease.
- Osteochondrosis manifesta: subclinical, macroscopic and radiographic signs.
- Osteochondrosis dissecans (osteochondritis dissecans): cartilage flap
Are male or female dogs more frequently affected by osteochondrosis?
Male dogs aside from OCD of the talus.
Large and giant breed dogs are most commonly affected.
What are the most common sites of osteochondrosis in the dog?
- Humeral head
- Medial and lateral (most common) femoral condyles
- Medial and lateral trochlear ridges of the talus
- Medial aspect of the humeral condyle
How much growth are the growth plate and epiphyseal ossification centres responsible for, respectively?
Growth plate: 75-80%
Epiphyseal ossification centre: 20-25%
At what age are epiphyseal ossification centres typically closed with remaining growth occurring only through the growth plate?
Around 26 weeks of age
What are the ages of complete fusion of the growth plates in dogs?
What constrains circumferential expansion of the growth plate during growth?
Perichondral ring of Lacroix
What are the zones of the growth plate?
- Resting zone.
- Proliferative zone
- Hypertrophic zone
- Zone of mineralization.
What is the only zone of the growth plate that is vascularized?
The resting zone, via chondroepiphyseal vessels
What are the two distinct layers of the articular epiphyseal complex in the developing bone?
Outer layer: avascular region that becomes articular cartilage. Does not participate in endochondral ossification.
Inner layer: similar to the growth plate in that it is responsible for epiphyseal enlargement, but it is relatively disorganized and has abundant vasculature from the chondroepiphyseal vasculature.
What are the layers of mature articular cartilage?
- Superficial zone.
- Transitional zone
- Radial zone
- Tidemark
- Zone of calcified cartilage
Does conversion of cartilage into bone occur at the periphery or toward the centre of the epiphyseal-articular complex?
Toward the center
How are anastomoses between the cartilage canals of the chrondroepiphysis (from the perichondrial plexus) and the epiphyseal bone marrow vessels thought to play a role in the development of OCD?
FIGURE 73.5 Theoretical model of articular osteochondrosis. A, Anastomosis between cartilage canal vessel (red) in the epiphyseal cartilage (blue) and the distal bone marrow vessels. Note the direction of blood flow (arrowheads). B, Cartilage canal vessel now receives blood from a vascular anastomosis with the bone marrow vessel that crosses the mineralization front obliquely. C, Mechanical stimuli damage the new anastomosis, resulting in a necrotic cartilage canal (ncc) and subsequent cartilage necrosis.
What are some proposed risk factors for development of OCD?
- Hereditary (including anatomic/conformation). Strong prediposition of breeds suggests a hereditary component.
- Macro and microtrauma: macrotrauma mays propagate formation of OCD lesions, but has not been demonstrated as an initiating factor for osteochondrosis. Microtrauma may result from limb conformation or joint shape, but is not consistent with the predisposition of OCD in the caudal aspect of the shoulder (not the primary weight bearing surface).
- Dietary: high calcium and vitamin D have been associated with OCD in Great Danes but not other breeds.
- Rapid growth: predisposition of large breed dogs to OCD supports this theory. A direct role of overnutrition in development of OCD has not be definitively proven.
What are the two types of osteochondrosis lesions as proposed by Olsson and Reiland?
Type 1: Lesion occurs at the center of the affected articular surface, away from vascular attachments (i.e. OCD of the humeral head, femoral condyles, humeral trochlea).
Type 2: Lesion occurs at the joint margin and retains a vascular attachment (i.e. trochlear ridges of the talus, fragmented MCP)
What is the proposed etiology of articular OCD lesions?
What is the grading scheme for OCD lesions?
What might occur to cartilage lesions following elevation in cases of OCD?
Type 1: may detach and become joint mice, or remain attached (may undergo heterotopic calcification).
Type 2: typically produce bone by endochondral ossification.
What is the proposed etiology of growth plate OCD lesions?
Characterized by persistence of hypertrophic chondrocytes (as compared to cartilage necrosis with epiphyseal OCD).
Thought to be due to vascular disruption to either the epiphyseal (cartilage canal) or metaphyseal vessels (see image).
What is a potential example of a growth plate manifestation of OCD?
Retained cartilaginous core (typically distal ulna)
What diagnostics might be useful in the work-up of potential OCD?
- Survey radiography (+/- contrast arthrograms).
- Ultrasound (operator dependent).
- CT/MRI (cartilage may be too thin in dogs to accurately assess on MRI).
What are typical radiographic findings associated with OCD?
Disruption of the subchondral bone, with flattening or concavity of the normal bone contour, possibly with sclerotic margins.
What are some methods of osteochondrosis prevention?
- Breeding based on EBV.
- Control of energy intake and diets with low calcium content (although benefits of these measures amongst the general dog population have not been established).
What are treatment options for osteochondrosis?
- Conservative management (NSAIDs, rest, crate confinement, dietary restriction/well-balanced diet v. rigorous activity in an attempt to break off the flap):
a. For patients with small subchondral lesions, mild lameness/assymptomatic, and no joint mice (or in clinically irrelevant location).
b. For older patients in which removal of the OCD is considered equivocal. - Surgical management: aims to restore pain free function, and to prevent/delay/diminish OA. Generally consists of flap excision and joint mouse retrieval.
Should cartilage surrounding an OCD lesion be bevelled or squared off at the time of surgery?
Squared off (bevelled edges have been reported to impede fibrocartilage formation)
What categories of techniques exist for the treatment of OCD?
- Palliative: designed to provide symptomatic relief by removal of potential sources of irritation and inflammation.
- Reparative: Aim at enhancement of natural defect healing by bone marrow stimulation.
- Restorative: attempt to restore focal cartilage defects with biologic or synthetic abutments.
What are some palliative repair techniques described for the treatment of OCD?
Debridement and lavage
What are some reparative repair techniques described for the treatment of OCD?
Curettage, spongialization, abrasion athroplasty, forage, microfracture
What are some disadvantages of curettage, spongialization, and abrasion arthroplasty?
Involve the debridement of eburnated bone down to healthy bleeding subchondral bone, or to the cancellous bone (spongialization). This may involve removal of excessive amounts of bone and inadvertent removal of healthy tissue. Removal of a large bony defect also creates an abnormal contour onto which for the cartilage to form.
Less aggressive techniques involve forage or microfracture which preserve the subchondral bone plate.
It is important to ensure removal of what layer when performing microfracture for OCD lesions?
The calcified cartilage layer should be carefully removed to exposure the subchondral bone.
Second generation techniques involve the addition of growth factor or matrix augmentation.
What are some restorative repair techniques described for the treatment of OCD?
Fragment reattachment, osteochondral transplants (OATS), synthetic osteochondral resurfacing (Synacart).
What is the most common donor site for dogs undergoing OATS for dogs?
Medial sulcus terminalis or medial and lateral trochlear ridges of the femur
What are the main issues associated with use of osteochondral autografts in the treatment of OCD?
Donor site morbidity, varied thickness and quality of cartilage depending on the site of collection (non-weight bearing grafts may not adjust well to their new location).
Xenografts and allografts have been introduced to address these concerns, but chondrocyte viability is a concern.
What is the biggest issue with use of SynACart implants for treatment of OCD?
Large diameter and depth of receiving socket may limit revision options in instances of implant failure.
What implant is depicted in the image from Murphy 2019 in Vet Surg?
Synthetic osteochondral resurfacing implant (A: first generation, B: second generation).
