Equine Leg Anatomy: Part Four

Part Four: Hocks and Stifles

The hind end of the horse plays important roles in propulsion (as in a racehorse) and collection (as in dressage & jumping).    Naturally, horses carry more of their weight on their front legs than their hind legs.  This is one reason horses more often exhibit lameness in the feet and tendons/ligaments of the front legs. 

However, disciplines that encourage the horse to carry more weight with the hind end and to sit in collection, or those with as much thrust as racing or jumping, can cause issues for the hind end.  This is due to increased flexion and concussion, requiring the hock joint to serve as a shock absorber for most or all of the horse and rider’s weight. The most common areas of concern are the hocks and the stifles which are connected by the reciprocal apparatus.  This apparatus ensures that whenever the hock flexes, the stifle does also and vice versa.

Hocks

The hock of the hind leg is really like the human ankle.  It is comprised of 3 rows of tarsal bones and has 4 separate joints.  The top joint is the only joint which actually moves and causes the flexion of the lower leg.  However, usually this joint is the not the joint which develops arthritis or Osteochondrosis (OCD).  Arthritis is typically found in the lower 2 joints of the hock due to wear and tear and possibly poor conformation in middle-aged sport horses. Hocks with a greater angle when the horse is standing still withstand the pressures of sport horse disciplines better than those are too upright (according to this article, 154-159 degrees is ideal). 

You might notice a bog spavin or puffiness around the hock joint.  This is caused by fluid in the joint and can be due to trauma (i.e. kicked by another horse) or arthritis or OCD.  The horse may also exhibit pain by unwillingness to step up under his body or take a certain lead when cantering, etc. 

Treatment of inflammation in the hocks includes cold-hosing or ice boots, feeding joint supplements, injections of Legend and/or Adequan and may culminate in injections (of corticosteroid or hyaluronate) into the lower 2 hock joints. You can help prevent arthritis issues in the hock joint by properly conditioning your horse for the work expected of her, giving him time off to rest after a difficult ride (a day off), and not over-working the already tired horse. 

By contrast, OCD is found in very young horses and is developmental.  OCD occurs when cartilage doesn’t properly convert into bone and lesions form.  Vets believe OCD is caused by dietary imbalances in the amount of zinc versus copper, over-feeding, and possibly poor genetics. Surgical removal of lesions, while invasive and expensive, is often successful with gradual rehabilitation.

Stifles

The horse’s stifle joint, though very high up off the ground it akin to a human knee.  It connects the femur to the tibia and has a patella (i.e. knee cap). 

Horses resting with left stifles locked

The most common issue that can occur in the stifle is locking stifles, i.e. the upward fixation of the patella.  While it is normal for horses choose to lock their stifles when at rest (this enables them to stand while sleeping), it’s abnormal when it occurs during any movement.  To a rider, it can feel like the horse tripped as often it is but a momentary hitch.  However, in extreme cases, the horse can be stuck with a locked stifle for days.  

Locked stifles can be caused by poor conformation or insufficient strength in young horses or those who have been out of work and are returning to it.  In these cases, a gradual training program can strengthen the horse’s body and remove the issue altogether.  Once, my mare’s stifle locked after a week off of work because all she had was walk in her paddock from the hay to the water.  Regular exercise (whether human-initiated or equine-initiated) can help prevent locking stifles.

Conclusion

Horses are an orthopedic masterpiece or nightmare, depending on how you look at it.  It’s amazing how efficiently and athletically they function, however they’re also very prone to a variety of issues and breakdown.  Careful conditioning and good nutrition and appropriate rest all contribute to keeping your horse sound and healthy well into their 20’s.

My Holsteiner mare Kaleidoscope, who turned 20 today!

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