EQUINUS

What is Equinus?

One of the most overlooked problems affecting the lower extremity is a condition known as "Equinus".

The term "Equinus" is derived from the word "equus", Latin for "horse".  It is also where we get the word "equestrian".  

In this case, the term refers specifically to the horse's foot.  

As you can see in the picture on the right, horses bear weight not with their heel bones, or even with the ball of the foot.  Rather, horses actually bear weight on the tips of their toes.  Note in the cross section of the horse's foot on the right that that only the three toe bones are even visible, and the weight is being borne on the tip of the last toe bone.    

 
Acute founder

A horse's foot in cross-section.  
Note that the entire weight-bearing portion of the  foot 
consists of the three toe bones, 
with the weight being born on the tip of the last toe bone.

A horse, then, is permanently in pretty much the same position as a ballerina when she's in the "en pointe" position--when she stands on the very tips of her toes.

In fact, the term "Equinus" is used in humans to describe the same sort of condition when it occurs pathologically--where the foot exists in an abnormally "plantarflexed" position, (with the foot bent downward at the ankle) position.  

The foot pictured to the right exhibits a rather severe equinus deformity.   This patient would not even be able to get the heel bone anywhere near the ground to bear weight.

Besides being used to describe a foot where the foot is rigidly plantarflexed, structural equinus"), podiatrists also use the term in another way.  

Severe Equinus position of the foot

Podiatrists also use the term "Equinus" to refer to the condition where the foot may look normal, (not being in a plantarflexed position), but when it simply has a diminished ability to bend up at the ankle--a motion called "dorsiflexion".

The normal foot usually has at least 10 degrees of dorsiflexion past being perpendicular to the leg, as indicated in the diagram to the left.  

Normal ankle dorsiflexion-
a non-Equinus foot-type

To the left we see a foot that is able to dorsiflex, or bend back at the ankle, at least 10 degrees.  

This would be considered normal range of motion, and a normal foot insofar as equinus is concerned.   

If a patient cannot bend the foot up as much as he should, however, he may be thought of as though he functioned with an equinus foot.  So this condition is sometimes known as a "functional equinus".

To the right, however, we see a foot that is not able to dorsiflex 10 degrees.  In fact, this foot is unable to bend upwards at all, remaining perpendicular to the leg.  

While clearly not a "structural" equinus with the foot being held rigidly in a plantarflexed position like the horse's foot, the ballerina's "en pointe" position, or the "severe equinus" picture above, the foot's inability to bend up at the ankle makes this a good example of a "functional equinus". 

Patients with a functional equinus have particular difficulty when the body weight is transferred forward through the gait cycle.  This is when the foot really needs to be able to dorsiflex at the ankle.

Why does the foot get positioned in this way with equinus?

There are two ways this may happen.  The first way is when the bones of the foot are fixed in such a way that the foot is unable to bend upwards adequately at the ankle.  The second way an equinus deformity may be seen is when it is the soft tissues (muscle, tendon, ligament, e.g.) that prevent the ankle from bending upwards.  

What kinds of problems does Equinus cause?

Equinus can cause all sorts of problems for the patient.  As a patient transfers his weight forward, It can cause a strain or tear in the tight Achilles tendon, creating Achilles tendinitis or Achilles tendon ruptures, it can change the normal biomechanics of the foot, causing the foot to pronate excessively.  Arch strain (fasciitis), bunion deformities, hammertoes, neuromas, and a host of other problems may result.  

In fact, so important is it to recognize equinus that ignoring this condition can make it immensely difficult to treat any of the above foot disorders.  

What Causes Equinus?

Equinus can be caused by several possible reasons.  Several of the most common causes are:

  • Poor shoe choices:

    Chronic use of high heel shoes can create equinus as the muscles in the back of the leg contract to adapt to the abnormal position the shoes create.  Women who have worn high heel shoes for years will often have feet that cannot even feel comfortable in anything other than a 1", 2", or even 3" heel height.

  • Biomechanical causes: A weak muscle group on the front of the leg may be overpowered by the large muscles on the back of the leg. 

  • Neurological causes:  A neurological condition may cause the posterior muscle group (the back of the calf) to overpower the muscles on the front of the leg, pulling the foot into equinus over time. 

  • Traumatic causes:  Patients who have had severe muscle damage to the back of the calf, substantial scar tissue, an Achilles tendon rupture, or any of a host of other trauma, will tend to develop equinus because the tendon has healed tighter in a scarred-down position.

  • Iatrogenic causes:  "Iatrogenic" means that the condition is caused by the doctor.   An example of a doctor creating equinus is when the patient is casted in an plantarflexed position.  This is common, for example, when we try to cast the foot in this way to decrease the pull on the Achilles tendon while it heals from an injury.  Excessive scar tissue following surgery on the Achilles tendon is another example of an iatrogenic cause of equinus.

  • Congenital causes:  Sometimes the muscles on the back of the leg may be too short or contracted from the position in the womb. 

  • Bony causes:  A bony blockage may be preventing the ankle from bending upwards, resulting in what's known as a 'bony equinus'.   Arthritis, trauma, tumours, and fractures are examples of some of the more common reasons abnormal bone formation will form to create equinus.

How Do You Treat Equinus?

In most cases, equinus may be treated by proper stretching.  Muscle strengthening of the anterior leg muscle group or addressing any neurological factor contributing to the condition may be indicated.  Surgery may be indicated to lengthen contracted soft tissue, or, in cases where a bone is blocking movement of the ankle joint, surgical intervention may resolve the bony blockage creating the equinus.   

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