the horse picks the limb up to advance it cranially.
Infrequently, an audible “snap” or popping sound is also evident during exercise (particularly walking).
In many instances, upward patellar fixation can be produced in affected horses by manually forcing the patella upward and outward.
The examiner may actually be able to keep the pelvic limb locked in extension using minimal effort.
Since the problem is usually secondary to conformation and/or level of fitness, it is almost always bilateral.
However, affected horses historically exhibit clinical signs in one pelvic limb.
It is not until the more affected limb is successfully treated that a problem in the contralateral limb is manifested.
How is upward patellar fixation treated? Currently, there are 5 forms of treatment for intermittent upward patellar fixation: q Exercise: Lack of fitness results in decreased thigh muscle and patellar ligament tone.
With decreased supporting muscle and ligament tone, it becomes easier for the patella to lock on the femur and harder for it to replace within the trochlear groove.
In subtle cases of upward patellar fixation where conformation is relatively good, increased exercise alone may result in resolution of the problem.
We frequently ask the client to grade the level of their horse’s current level of fitness on a scale of 1 to 10 (1=very unfit; 10=extremely fit).
We suggest achieving a fitness level of at least 7-8 (if possible) prior to pursuing other forms of treatment.
This will rule out unfitness as a major contributor to the problem as well as increase the effect of other therapy. file:///C|/Documents and Settings/JC/Mis documentos/Arreg…Catedra/Locomotor/Horse Lameness (enganche rotuliano).htm (7 of 13)09/12/2005 22:03:56 Horse Lameness q Corrective Shoeing: Since fixation of the patella occurs when the pelvic limb is extended, prolonging the extension phase of the stride can make “unlocking” more difficult.
Alternatively, shortening the amount of time the pelvic limb spends in extension allows the horse to unlock his/her patella before the distal patellar ligaments become excessively tight.
Since the conformation of the distal pelvic limb and/or the toe length is intimately related to pelvic limb breakover, the farrier can frequently alleviate the problem via corrective trimming/ shoeing.
Rolling and/or rockering the toe of the shoe, applying a full (egg-) bar shoe, and/or the use of wedged pads (when needed) are commonly used techniques.
In many cases, we are able to help the pelvic limbs break over before intermittent upward patellar fixation occurs.
Hormonal Therapy: The administration of estrogen has shown to prove benefical for some horses exhibiting intermittent upward patellar fixation.
The presence of estrogen within the body of the horse may increase tension of various supporting ligaments.
These include the collateral, suspensory, cruciate, and distal patellar ligaments.
Increasing distal patellar ligament tension helps to relocate the patellar further distad, thereby making upward patellar fixation more difficult.
This in turn may alleviate clinical signs.
It should be noted that estrogen is also a powerful behavior modificator in the horse.
It is often used for stallions and geldings that are excessively difficult to handle, aggressive towards people or other horses, or overly anxious at shows and other events.
Estrogen is very effective at reducing anxiety and resistance as well as improving overall q q file:///C|/Documents and Settings/JC/Mis documentos/Arreg…Catedra/Locomotor/Horse Lameness (enganche rotuliano).htm (8 of 13)09/12/2005 22:03:56 Horse Lameness behavior in these horses.
Treatment usually consists of 2 injections of estrogen (25mg) in the muscle twice weekly for 4 consecutive weeks, then as needed therafter.
Administration of estrogen to mares usually causes them to exhibit clinical signs of estrus (heat).
Since this change in behavior is generally undesirable, we do not recommend its use in mares. q Intraligamentous Infusion of Counterirritant: This form of therapy is usually referred to as “blistering”.
Blistering involves the inject of an irritative substance into soft tissue(s) in an attempt to create an inflammatory reaction.
The irritative substance usually consists of iodine 2% in an almond oil base.
This substance can elicit an inflammatory response for up to 30 days depending on the amount used and the location of injection.
It is important to remember that fibrosis and scar tissue formation within normal soft tissues will occur as a result of severe inflammation.
As you know, scar tissue does not function like normal soft tissue.
Therefore, blistering in certain areas may inhibit proper function of associated soft tissue.
It is for this reason that The Atlanta Equine Clinic typically does not institute blistering as typical form of treatment for soft tissue problems.
However, in the case of intermittent upward patellar fixation, we gain a biomechanical advantage by replacing normal tissue with scar tissue.
The infusion of counterirritant within and around the medial and middle patellar ligaments results in the elicitation of an intense inflammatory reaction by the horse’s body.
With inflammation, file:///C|/Documents and Settings/JC/Mis documentos/Arreg…Catedra/Locomotor/Horse Lameness (enganche rotuliano).htm (9 of 13)09/12/2005 22:03:56
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