Hip Dysplasia & Avascular Necrosis

Question 1

What are the 2 views used to view the pelvis on radiographs?

Answer 1

1. ventrodorsal - extended leg
2. right lateral - right limb pulled cranial, left pulled caudal (no superimposing stifle joint), obturator foramina superimposed

Question 2

What 3 normal structures should be seen on a pelvic radiograph?

Answer 2

1. obturator foramina should be equal in size and position
2. patellae are central over the distal femoral trochlea
3. femurs are parallel and equal in length

Question 3

What additional view is used in specific situations for pelvic radiographs? Why?

Answer 3

VD frog leg positioning with hips flexed

assessed femoral capital physeal or neck fractures

Question 4

What is the normal depth of the acetabulum? What is the shape of the femoral head?

Answer 4

acetabulum should cover at lead 50% of the femoral head

there is focal flattening of the medial femoral head at the insertion of the ligament of the femoral head

Question 5

Normal pelvic radiographs:

Answer 5

• femoral head within acetabulum without subluxation
• bilaterally symmetrical obturator foramina, patellae, and femurs

Question 6

What causes hip dysplasia? In what animals is it most common?

Answer 6

heritable polygenic trait that also affects growth rates, diet, and physical conformation

large breed dogs, cats

(bilateral most common)

Question 7

What are the 6 major Roentgen signs associated with hip dysplasia?

Answer 7

1. incongruency between femoral head and acetabulum with subluxation of the femoral head
2. less than 50% coverage of femoral head by dorsal acetabular rim
3. periarticular osteophyte formation
4. enthesophyte formation
5. remodeling of femoral head and neck (thickening)
6. eburnation - osteosclerosis of subchondral bone of the acetabulum with thickening and loss of normal articular cartilage

Question 8

Where is enthesophyte formation most commonly found in hip dysplasia?

Answer 8

• joint capsule
• obturator and gemelli insertions on femoral neck

Question 9

Hip dyplasia:

Answer 9

• subluxation with decreased coverage of femoral head
• osteophyte formation on acetabulum rim
• enthesophyte formation at joint capsule and femoral neck

Question 10

Hip dysplasia:

Answer 10

• eburnation and subchondral sclerosis
• osteophyte formation on R and fractured osteophyte on L
• synovial hyperplasia due to cystic lesion seen on CT

Question 11

What are the 2 ways of certifying hip dysplasia in the United States?

Answer 11

1. Orthopedic Foundation for Animals (OFA) - extended leg view VD at 2 years of age, not an open registry
2. PennHip laxity testing - 3 view extended VD, non-compression frog-leg VD, and compression (stress) frog-leg VD; laxity compared to standard of breed; tested at 4-6 months with an open registry

Question 12

What is avascular necrosis of the femoral head (Legg-Calve-Perthes Disease)? How does acute and chronic affects differ? What breeds are most affected?

Answer 12

loss of blood supply to the femoral head typically secondary to a capital physeal fracture or femoral neck fracture

• ACUTE = lameness, no radiographic features
• CHRONIC = lameness, muscle atrophy

small and toy breed dogs, cats

Question 13

What are the 4 Roentgen signs of chronic avascular necrosis of the femoral head (Legg-Calve-Perthes disease)?

Answer 13

1. flattening, irregularity, and/or osteochondral fragmentation of femoral head
2. remodeling and osteolysis of femoral neck (apple core)
3. osteoarthritis
4. widening of coxal joint space

Question 14

Avascular necrosis of the femoral head (Legg-Calve-Perthes disease):

Answer 14

• normal R
• marked remodeling of femoral neck
• muscle atrophy of L pelvic limb

Question 15

Avascular necrosis of the femoral head (Legg-Calve-Perthes disease):

Answer 15

• remodeling of the L femoral neck

Question 16

Avascular necrosis of femoral head, frog-leg:

Answer 16

• R femoral neck moves in an abnormal way