AQHA November / December 2019 Magazine AQHA NOV-DEC 2019 PRINT (2) | Page 22

PG.20
HORSE HEALTH
(Figure 1)
Title: The Anatomy of the Domestic Animals Author: Septimus Sisson Publisher: W.B. Saunders Company, 1914
Upward fixation of the patella (also known as ‘intermittent
upward fixation of the patellar’, ‘delayed patellar release’,
‘stifled’, ‘catching stifles’, ‘locked stifles’ and ‘sticky
kneecaps’) occurs when there is some degree of hesitation
in the movement of the patella back into its gliding
position. It can be subtle and difficult to detect or extreme
- where the stifle becomes locked and the horse is unable
to flex its leg at all. More often it is in between, the signs
varying with the severity. It may last for a moment or a
few minutes - or even be permanent; it can occur daily,
weekly or occasionally.
A locked stifle is very obvious and can be alarming – the
horse standing with the hind leg locked straight and stiff in
extension, the fetlock and hoof flexed and maybe dragging
the toe of the hoof along behind them. Temperament
affects how they react – some will panic and strenuously
try to release their leg. Usually, the leg will unlock of its
own accord, but some horses may need assistance. When
the patella catches momentarily and its release is delayed,
the stifle and hock can show an exaggerated flexion –
that can be confused with stringhalt. In less severe cases
the horse’s stifle locks intermittently when the horse is
moving, the leg appearing to collapse briefly and then
unlocking itself with a loud click.
In its most mild form stifle lock can be quite difficult to
diagnose as affected horses may not always show classic
locking, but they have more subtle signs - shortened
stride, difficulty picking up or maintaining a canter lead,
scrambling movement while going up or down hills; a
jerky gait during transitions. Signs are often worse after
rest, during cold weather or with anxiety, and in some
horses the ‘delay’ or ‘lock’ may temporarily resolve only to
recur after taking a few steps. Repeated delayed release
of the patella can cause stifle soreness and unwillingness
to work, although obvious lameness is unusual. Miniature
horses and ponies have a higher incidence of locking
patellas, and in Shetland ponies it increases the risk of hip
displacement.
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