One of the most overlooked problems affecting the lower extremity is "Equinus". "Equinus" refers to the condition where the foot is unable to bend upwards adequately at the ankle.  

Most sources cite the 10 degree rule: you should have at least 10 degrees of ankle movement for normal walking.

The diagram to the right demonstrates a foot that is able to bend upwards at the ankle at least 10 degrees.

The diagram to the left demonstrates a foot that is not able to bend upwards 10 degrees or more at the ankle.  In fact, this foot can't get much past 90 degrees relative to the leg.  This foot, therefore, would be defined as a foot with equinus.

Because it cannot bend upwards properly in gait, the equinus foot functions with relatively more pressure borne on the ball of the foot, and relatively less pressure borne on the heel.  As you need to be able to bend the foot at the ankle approximately 10 degrees, patients with equinus can develop all sorts of foot complaints, including common conditions like bunions, metatarsalgia, tendinitis, Achilles tendinitis, arch pain, and abnormal gait.

In mild or moderate cases, equinus may not be obvious, and an effort must be made to look for it.  In severe cases, equinus can cause the patient to be completely unable to get the heel on the ground, and the patient is forced to stand on the ball of the foot. 

The word "Equinus" sounds like "Equestrian"

In fact, both words derive from the Latin word for horse.  This is because horses (along with many animals) actually stand on the forefoot--with their heel high up off the ground, never bearing any weight. 

This position allows them to accelerate more quickly, and to run faster.

(See diagrams below.)  

The femur, or thigh bone, is located here, well into the horse's chest.  The knee joint is located way up here almost at the level of the neck.  As you can see it bends back in the same direction as our knee does.

The heel bone is located way up here.  Clearly, it bears no weight whatsoever.    The ball of the foot is located here.  Only the toe bones have any contact with the ground in the horse, as you can see below.

A cross-section of a horse's hoof demonstrates that the weight-bearing portion is actually comprised only of the toe bones.  No other bones in the horse's foot actually come into contact with the ground.

Of course, this degree of toe-walking is exaggerated in animals such as the horse, and in horses it is, of course, normal.  But in humans, equinus deformities may lead to increased pain and pressure in the ball of the foot, which may lead to deformity.   

What Causes Equinus?

Equinus can be caused by several possible reasons. 

• A weak muscle group on the front of the leg may be overpowered by the large muscles on the back of the leg.  This will slowly pull the foot downwards into equinus over time.
• The muscles on the back of the leg may be in spasm as a result of a neurological condition, and may overpower the muscles on the front of the leg, again pulling the foot downwards. 
• The muscles on the back of the leg may be simply too short or contracted. 
• A bony blockage may be preventing the ankle from bending upwards, resulting in what's known as a 'bony 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 to lengthen the Achilles tendon may be indicated in some cases unresponsive to stretching.

In cases where a bone is blocking movement of the ankle joint, thereby resulting in equinus, the bony blockage may have to be removed surgically.