Page 402 - The Veterinary Care of the Horse

• traumatic injuries

• osteochondrosis
VetBooks.ir • bone cysts

•
infection
• degenerative joint disease.

The equine stifle joint also has the unique problem of upward fixation of the patella.

Upward fixation of the patella

This is a condition where the horse or pony is temporarily unable to unlock the stifle from the

extended position. The medial patellar ligament stays hooked over the medial trochlear ridge.
The problem may occur in one or both hind limbs.

CAUSES

Horses with straight hind limbs, e.g. some Warmblood breeds, are prone to upward fixation
of the patella but it is generally more common in ponies and cobs. Shetland ponies have a

high incidence and in some cases the condition is considered to be hereditary.
Young, unfit or poorly muscled animals are also particularly susceptible. Any condition

causing debility or sudden loss of quadriceps muscle tone can lead to the upward fixation of
the patella in vulnerable horses. This includes those with injuries and stifle pain.

CLINICAL SIGNS
• The stifle and hock are locked in extension and unable to flex and so if the horse is made

to move it hops forwards with the leg extended behind it (Figure 8.24).

• The fetlock is flexed and the toe is dragged on the ground.
• The condition tends to occur after the animal has been standing still.

• It can lock for a few strides or for a prolonged period of time.

• When the stifle unlocks a ‘snapping’ sound may be heard and the limb may jerk up

quickly in a fashion resembling stringhalt.
• If the condition is severe the condition can lead to swelling of the stifle joint and

lameness.