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Here is one article found on Leggs Perthe - Not the bolded area

Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Key Points

A disease of the hip joint that results in abnormal deformity of the ball of the hip joint
This is a disease primarily seen in small breed dogs
Treatment is femoral head and neck excision
Prognosis is very good, providing that rehabilitation therapy is done after surgery
Same disease but different names (synonyms)
Calve-Perthes disease
Legg-Perthes disease
Avascular necrosis of the femoral head
Coxa plana
Osteochondritis juvenilis
What is it?
A disease of the hip joint that results in abnormal deformity of the ball of the hip joint
The disease starts with an insult to the blood supply to the head of the femur bone
As the blood supply is damaged, the bone dies off
The bone in the femoral head collapses and the cartilage coating of the femoral head becomes cracked and deformed
Arthritis or inflammation of the hip joint results, which causes pain and lameness
Cause
Not completely understood
Genetics - can be autosomal recessive gene in some dogs
Injury - compression of the vessels of in the femoral head
Abnormal sex hormone activity - preconcious
Because of the potential heritability of this disease, affected dogs should not be bred

Signalment
Typically dogs that are less than 1 year of age (5 to 8 months of age is most common with peak incidence around 7 months of age)
Breeds commonly affected
<UL type=circle>Yorkshire Terriers - most common breed
Westies
Many other small breed dogs
</UL>Equal risk for males versus females

Clinical signs
Irritability
Chewing at hip of flank region
Progressive lameness (may take about 2 months until dog is not bearing any weight on limb)
Stiffness of affected limb (85 to 90% of dogs have only one hip affected)
Atrophy of muscles of affected limb
Pain when moving the hip - especially when extending the limb backward and also to the side
Crepitus or crunchy feel of the hip joint on range of motion

Diagnosis
Physical examination - hip pain
Radiographs
<UL type=circle>flattening of femoral head
lucencies of femoral head
bone spurs - arthritic degeneration
increased joint space
Below is a radiograph of the hips of a Yorkie that has the disease; take note of the moth-eaten appearance of the femoral head (below left and right)
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