Hypothesis Three: Joint Luxation

Due to the fact that the patient is a puppy, it could have hyperextended its hip joint during 
play.  During hyperextension, the femur acts as a lever against the femoral head.  True 
luxation occurs only when the joint capsule, the teres ligament, and the musculature 
around the joint have been severely traumatized.   Usually the femoral head luxates 
cranially and dorsally to the acetabulum.  The inflammation due to this trauma would 
result in joint laxity and pain, leading to severe lameness.

Orthopedic examination under sedation would reveal that the affected limb is shorter 
during full caudal extension and full normal extension.  Also, the affected limb appears 
longer on full cranial extension.  You would detect crepidation upon flexion, extension or 
rotation of the joint.  A positive Ortalani sign would indicate laxity in the affected joint.  
On palpation, a wider space between the bony prominences of the trochanter major and 
the tuber ischii  can be detected.  The trochanter major of the affected limb will appear 
more elevated on comparison with the normal limb.  Many of these signs can be 
confirmed radiographically.