Upward Fixation Of The Patella In Horses

We have all seen horses with a hind limb stuck out behind them, unable to flex and protract the limb. Often we are told that there is nothing much to be done, and that the horse will outgrow the condition.

But of course, we can never be satisfied with that advice. When we break it down and look at the condition logically, we will see that not only is it imperative that we intervene, but there are, in fact, many things we can do to help these horses.

 

What is involved

According to Jennifer H. Brooks, the stifle is the largest and most complex joint in the horse, and can also be the weakest. The stifle is made up of the joint between the femur and the tibia, and the joint between the femur and the patella. The femorotibial joint is subdivided into a medial and a lateral compartment. The patella will slide proximally and distally along the intertrochanteric groove of the distal femur, and can be hooked over the medial trochlear ridge of the femur to act as a part of the stay apparatus of the hindlimb, preventing the stifle joint from flexing. The quadriceps femoris and tensor fascia latae insert on the intermediate patellar ligament and are responsible for moving the patella in and out of this locked position. The patella has three ligaments: a medial, intermediate and lateral ligament, which you can learn more about in a Research Refresh shared in the Onlinepethealth Equine membership.

When upward fixation of the patella occurs, there is a failure of the patella to disengage from its locked position on the intertrochanteric groove. The movement of the patella is caused by the contraction of the quadriceps femoris and the tensor fascia lata, as mentioned above, and for this reason the factors that cause UFP or intermittent UFP (IUFP) are related to these structures.

Factors that can contribute to the development of UFP include conformational faults, abnormal stifle angulation, a sudden growth spurt and pregnancy.

 

Clinical significance of stifle dysfunction

Although these conditions can often spontaneously correct, we must consider the significance of the stress placed on the patellar ligaments, together with the abnormal movement and stress placed on the joint. From our Research Refresh, we know that patellar ligament desmitis carries a poor prognosis for recovery. Any OA present in the stifle joint will be complex to treat and again, will carry a poor prognosis.

Add to the above possible structural complications a change in muscle recruitment and activation patterns, as well as muscle atrophy, and we are predisposing the horse to even more complications within the pelvic and lumbar region, and impacting their future ability to perform as athletes and remain sound.

 

How UFP has been treated in the past

Veterinary intervention in the past has included medial patellar ligament desmotomy, medial patellar ligament splitting, injection of caustic agents, estrogen therapy, corrective shoeing and trimming, rest and NSAIDs, and exercise conditioning, to name a few. If you would like to learn more about the medical management, please watch the webinar by Robyn Williams: Hind limb Pathology in the Onlinepethealth Equine Membership where she goes into depth on this condition. 

None of these protocols have resulted in a very good prognosis for this condition, and many carry the risk of secondary complications.

In the past, rehabilitation or physiotherapy has not been routinely incorporated into the recovery of this condition, but there is a great deal that we can do, and should do as a part of the #VetRehabTeam. 

 

Developing a treatment protocol

IUFP and UFP can be either secondary or primary, and thus a full assessment is essential. A primary cause could be a skeletal growth spurt, conformational faults, poor shoeing/trimming techniques, or muscle weakness due to inactivity. Any treatment protocol will have to take the primary cause and secondary results into consideration.

Together with the predisposing factors or causes, we need to consider that the abnormal movement of the patella will cause local irritation, leading to inflammation and pain as well as increased joint effusion, leading to further reflex inhibition and altered proprioception.

 

So in assessing our goals, we want to:

• reduce pain and swelling present in the stifle;
• decrease the abnormal wear of the articular cartilage;
• strengthen stifle musculature to optimise the patellar mechanics and the neuromuscular reflex;
• increase overall conditioning, including flexibility, core strength, proprioception and endurance of the musculature of the hind end, the abdominals and the top-line; and
• return the patient to function and previous levels of performance.

 

Your findings

Before we dive into the treatment protocols we might employ, let’s take a look at some of the common ways in which these cases might present to us:

• The owner may report their horse to be clumsy, tending to stumble or trip, or getting a hind leg stuck behind, or suddenly giving out or collapsing. An audible click or pop might be heard as weight is shifted on and off of the affected limb.
• Horses may present with an overweight body condition score, poor abdominal musculature, atrophy of the top line, and atrophy of the hindlimb muscles.
• The stifle joint may be painful, and oedema may be present on palpation. The cranial phase of the stride may be shortened, and an abnormal ‘jump’ of the patella may be seen as the horse moves.

It is important to perform mobility and stability testing of the hindlimbs, noting the mobility and restrictions in the affected limb, as well as the horse’s ability to carry weight and the muscle recruitment patterns employed to do so. Proprioceptive tests should also be performed through backing up and turning on the forehand.

In movement, these horses will have a poor connection from hind to front, a failure of the hindlimbs to track up, and trouble in performing balanced canter transitions and maintaining a balanced and united canter.

 

How can we help these patients?

A controlled, progressive and very intentional exercise protocol will be key over the course of several weeks to months. We need to specifically target the ability of the hindlimbs to fully flex and extend.

 

More movement, not less.

Environmental management is essential to allow the horse as much free movement as possible. Box rest will only worsen the effects of this condition. Ideally, horses should be on pasture 24 hours a day.

 

Address pain

It is likely that for some horses pain will be present as a result of the altered joint mechanics and irritation to the medial patellar ligament and local structures. This should be medically managed by a veterinarian to reduce inflammation and secondary muscle inhibition.

In addition, we have a variety of modalities at our disposal which can effectively address local pain, inflammation and dysfunction of both joint and muscle. These include everything from heat and ice, to laser, TENS, PEMF and manual therapies.

 

Stretch it out

Tight or restricted muscles need to be addressed through a stretching protocol, addressing the flexibility of the hip and stifle to ensure that a full range of motion is present.

Stretches that are valuable in this condition include holding the limb in a fully flexed position, stretching into protraction, as well as retraction of the limb, as well as stretching the limb craniomedially.

 

Strengthen

• Start with simple isometric muscle contractions. We want to use isometric contractions to activate and strengthen muscle without the involvement of joint movement to begin with. We can achieve this through weight shifting exercises, or a lateral tail pull, onto the affected leg in all functional positions of the leg. This can be progressed to leg lifts, and leg lifts with weight shifts.
• Once these exercises are going well, dynamic exercises can be incorporated, starting with hand walking where the horse is asked to move with activity and impulsion from behind. Backing up can be introduced as the next progression, and then slight inclines and declines, followed by variations in the surface the horse moves on.
• The next progressions include walk-trot transitions, turns on the forehand, and backing up and down inclines, followed by cardiovascular fitness work, such as lunging or longlining in a correct posture, incorporating ground poles, and hill work.
• Once horses are doing well on the above exercise regimen with no return of lameness and a significant improvement in the symptoms of UFP, they can be progressed to work under saddle, using the above exercises in a slow and measured progression.
• The use of the Equiband system, Kinesiotape, and any other tools that give proprioceptive feedback or added resistance can be valuable in these patients as we progress exercises.

 

Where to next?

As the horse returns to full work, it is important to continue utilising cross training and to target the strengthening of the hindquarters.  Try to include the above exercises in the normal routine of the horse on a weekly basis. Targeting and training regularly, and making use of proprioceptive feedback, can help prevent injury and recurrence of the UFP.

 

 

Resources

• Physical Therapy Approaches for Strengthening the Stifle and Pelvic Limb, Jennifer Brooks
• The Equine Limbs series
• The Equine Stifle: Selected Cases and their Rehabilitation, Dr Melanie Perrier
• The Whole Horse Approach to Equine Rehabilitation: Focus on Stifle Biomechanics, Sheila Schils
• Normal Ultrasonographic Anatomy and Injury of the Patellar Ligaments in the Horse