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Weak Stifle Muscles: Signs, Symptoms and Solutions 



Poor stifle function is common in working horses and usually goes unnoticed by trainers, owners and vets alike. Why? Because the signs can be vague and a small glitch in stifle function can be hard to see unless you look for it. Stifle weakness can slide past even seasoned diagnosticians; when looking for sources of pain in the hind limb, there are three joints that reciprocally flex together: the feltlock, hock and stifle. Prolonged pain in the hind limb can stress the sacroilliac joint as well, adding yet another layer. Sorting out which joint is the source of pain can take time, and Veterinary diagnostics. But it is well worth it, as this common stifle dysfunction is highly treatable if caught early. Not only are the outcomes frequently good, owners can dispense the rehabilitation themselves usually without medications. While the early signs are subtle, almost anyone can learn to spot them and bring them to attention of their vet.  

The stifle (the horse's true knee), has a patella just like ours. But there is a special system called the stay apparatus that allows horses to lock this joint while sleeping. The dysfunction occurs when the muscles that surround and support this sensitive system become weak. When the muscles do not have adequate tension and coordination, the medial patellar ligament becomes momentarily strummed on the trochlear ridge of the femur. This is painful and causes the horse to brace the limb, and lumbar spine. Over time the horse may develop arthritis or damage to the patellar ligaments. Which could be career ending. So thoroughly checking and monitoring the stifle is key.

Signs and Symptoms

Mild to acute lameness in the hind limb would be the most obvious symptom, but by the time this is present joint dysfunction has been ongoing for some time. If the horse is severely lame, the weakness may have progressed into a full-blown disease known as Upward Fixation of the Patella. This occurs when the entire pelvic limb becomes locked due to muscle weakness and joint instability.  The subtle signs of simple muscle weakness, show up much sooner. This is the ideal stage to arrest the problem for the best outcome.

Simple muscle weakness is usually bilateral so the horse in pain may shorten the stride of both hind limbs disguising any obvious limp. To compensate for stifle pain, horses will often change the flight pattern of the entire limb. If you view them walking away, they tend to move the whole limb in a circular pattern called circumduction. This is to avoid bending and flexing the joint, as full range of motion of the stifle may cause the catching effect which is painful.  

Horses in work will stumble in downward transitions, especially canter to trot. They may pin their ears and move hollow for a few strides while moving and then return to normal. Jumping may become very difficult and bucking upon landing can occur. This is often because the whole hind limb and all the reciprocal joints as well as the SI are impacted by the problem. Sacroilliac pain is commonly concurrent.

Horses will frequently have muscle spasms and pain in the long back muscles as the lumbar spine is overtaxed from frequent bracing. These additional compensations have to be addressed and treated along with the stifle weakness for a full recovery.


Check with your Hands

The stifle can easily be felt with your hands. Place your hand over and around the patella. In a standing horse the patella may move upward into its fixed position. Have a handler ask the horse to take a step forward while you leave your hand there. On a healthy stifle joint you’ll feel the patella glide forward into your hand in a smooth uniform movement.

In horses with stifle pain there may be fluid around the joint, and when asked to step forward you’ll feel a delayed action, and then the patella can abruptly jump forward. Sometimes you can hear an audible ‘clicking” sound. This is the strumming action of the medial patellar ligament momentarily catching on the trochlear ridge of the femur. A word of warning, horses who are in pain may not tolerate this touching and can kick. If this is the case, step back and simply visually appraise the movement. Always use good judgement and have someone help you.  

This is a helpful assessment for your use on your own horses’ joints. It takes time and lots of practice to actually differentiate, but it’s helpful for horse owners and trainers to be aware of what normal versus abnormal stifle function looks and feels like. This assessment will not replace a manual and lameness exam by a veterinarian who should be contacted to diagnose a true disfunction.  

Who’s Vulnerable?

Any horse may be affected, however horses with straight hind limb conformation are most vulnerable. Horses who are croup high are also commonly plagued.  It is typical to see young horses with croup high conformation suffer a bought of what’s commonly called “sloppy” stifles. This usually resolves as the horse finishes growing and becomes balanced or because they are put into training which tightens and stabilizes the joint.

Horses coming off prolonged rest due to another unrelated injury, may have weak stifles that need to be strengthened before returning to regular ridden work. Additionally, some horses due to their adult conformation will need regular stifle strengthening exercises as part of their maintenance programs.


Here’s the good news, horses with this diagnosis can make a full recovery so long as no permanent damage has occurred. It is critical to have a vet diagnose the muscle weakness and rule out any joint or ligament damage before beginning rehabilitation protocols.

Prescribed graduated exercise is the remedy; The quadriceps, biceps femoris, and tensor facia latae must all regain tone and coordination to recover the smooth gliding action of the patella.

Walking and trotting in straight lines and over ground poles is commonly the first step. Tail pulls to the side can be used to strengthen the tensor facia latae. And cavaletti are eventually incorporated as well. Simple additions to care such as cold hosing and NSAIDS are often used to help progress the rehabilitation.

It is also critical to address the long back muscles which may be painful and spastic due to bracing. Massage and core conditioning exercises are key in restoring healthy function of the lumbar spine.

For more information see my related article on the Equine Spine

Horse owners are usually able to dispense the required exercises with some guidance from a veterinarian and a rehabilitation assistant. It will involve spending lots of time with your horse, which most of us enjoy anyway. Or the rehabilitation can be dispensed by an experienced trainer at your own barn.

Be Informed

As horse owners we are the first line of protection and the best advocates for our animals. We know them better than anyone else because we spend the most time running our hands over them. We can learn to notice the earliest signs of subtle discomfort, and steer our companion athletes towards diagnoses and care.  We must stay informed about all aspects of horse health, including the musculoskeletal system.

The stifle is a critical joint and catching muscle weakness and accompanying joint dysfunction could prevent further lameness and associated joint damage. Strengthening the muscles that surround and support the stifle on any horse will only benefit his long-term soundness and increase his comfort and athleticism.