Ch 58 - Pathogenesis, Diagnosis and Control of Canine Hip Dysplasia

Question 1

When are the earliest gross changes of HD visible and what are they?

Answer 1

30 days
- Oedematous ligament of head of the femur with torn fibers and capillary haemorrhage
- Increased volume of ligament and of synovial fluid

Question 2

When are the first radiographic signs of HD visible and what are they?

Answer 2

7 weeks old
- Subluxation
- Underdevelopment of craniodorsal acetabular rim
- From 60-90d the degree of subluxation increased

Question 3

What two destructive event accompany subluxation?

Answer 3

• The forces crossing the joint increase as the force of the periarticular muscles increase to attempt stabilisation
• The area over which the forces are transmitted decreased (abnormal forces within the joint)

Question 4

What muscles help to reduce the femoral head when weight bearing?

Answer 4

• Gluteals
• Adductor magnus et brevis

Question 5

What is a luxoid hip?

Answer 5

A hip showing the most severe phenotypic characteristics of HD. It is permanently sub-luxated (or luxated) in all the phases of the gait cycle.

Question 6

What is the neutral stance of the hip?

Answer 6

• 10-15 deg of extension
• 10 deg of abduction
• 0 deg of rotation

Hip joint laxity is at its maximum when at a neutral stance

Question 7

What is considered a normal Norberg angle?

Answer 7

Over 105°

Question 8

What did the lifelong Labrador study highlight regarding age of HD?

Answer 8

• Only 55% of those whom would eventually develop HD, showed radiographic evidence by 6yo

Question 9

What distraction index is considered low chance of developing OA?

Answer 9

• Under 0.3

Question 10

What hormone may be associated with increased hip laxity?

Answer 10

Relaxin.
- It is elevated in last trimester of pregnancy and also in the milk of lactating bitches
- Last been associated with increased peripheral joint laxity in humans and dogs
- Higher levels found in Labs than Beagles

Gonadal hormones.
Non-neuter male Golden Retrievers are half as likely to develop clinical signs of HD by 4.4yo compared to intact males and those neutered after 12y of age.
- Neutering after 12mo seems to have a protective effect on clinical signs

Question 11

How does weight effect the development of HD?

Answer 11

• Heaviest male and female GSD puppies at 60d old had highest incidence of HD at maturity
• Overweight dogs develop radiographic OA 6 years earlier than lean counterparts
• Overweight dogs require medication 3 years earlier
• Lean dogs have a higher life expectancy by 1.8yr

Question 12

What nutritional factors may play a role in HD?

Answer 12

• High dietary Ca and excessive VitD (delayed endochondral ossification ans skeletal remodeling)
• High density anion gap diet (increased osmolality in synovial fluid and increased volume)

Question 13

How have injectable polysulphated glycosaminglycans been shown to effect development of HD?

Answer 13

Give to puppies from dysplastic parents as twice weekly injections from 6wk to 8mo reduced subluxation scores and reduced histopath evidence of arthritis at 8mo

Question 14

What are some common DDx for HD?

Answer 14

• Panosteitis
• OCD
• Hypertrophic Osteodystrophy
• CCLR
• LS stenosis
• Neoplasia

Question 15

What are common findings on the gait exam

Answer 15

• Wide or narrow based stance
• Hips or spinal sway
• Stiff, short-strided
• Bunny-hopping

Question 16

How many Ortolani negative dogs have an elevated distraction index?

Answer 16

50%

Question 17

What are the radiographic features of hip OA?

Answer 17

Femoral periarticular osteophyte formation
- caudolateral curvilinear osteophyte (CCO) (“Morgans line)
- circumferential femoral head osteophyte (CFHO)
- “puppy line” - gone by 18m, dont confuse with CCO

Subchondral sclerosis of craniodorsal aspect of acetabulum
Osteophytes of cranial or caudal acetabular margin
Joint remodelling from chronic wear
Flattening of the femoral head

Question 18

What are some of the main downfalls of the OFA, FCI and Kennel club?

Answer 18

• Voluntary film submission forming a large prescreening bias
• Not required to be evaluated later in life

Question 19

What views are required for PennHIP?

Answer 19

• VD extended (for comparison)
• Compression (shows congruency and true depth of hip joint)
• Distraction (quantification of the relative degree of femoral head displacement)

Question 20

What percentage of dogs with normal hip extended scored will have a positive Ortolani?

Answer 20

59%

Question 21

What kinematic changes are seen on gait analysis in dogs with HD?

Answer 21

• Increased hip extension at end of stance phase
• Incheased femorotibial flexion through stance and early swing phase
• Coxofemoral deceleration early in stance phase
• Increased stride length wtih decreased peak vertical force

Question 22

What are the critical characteristics of the ideal hip screening tool?

Answer 22

• Accurate (closely assoc with the unwanted phenotype)
• Precise (good interobserver agreement)
• Desireable to have a metric that is reprentable as a continuous scale
• Should be measureable as early as possible in life
• Must have a heritable component
• Selection pressure

Question 23

Define heritabilty

Answer 23

the ratio of additive genetic variation to overall phenotypic variation of a given trait

Question 24

How do you determine expected genetic change per generation?

Answer 24

Expected change in average litter phenotype after one generation =
Heritability (h^2) x (Avg parent - Avg population)

Question 25

What is the heritability of the PennHIP DI?

Answer 25

0.46 - 0.83

Anything above 0.5 is expected to make rapid changes

Question 26

What is the only hip scoring method which is highly correlated with the development of OA?

Answer 26

PennHIP

Question 27

What are the charcterisitcs of the optimal target phenotype?

Answer 27

• High heritability
• Selection pressure can be applied
• Highly correlated with the phenotype of interest