In an earlier post explained the tip and heel test (leave link). We saw how with this test could be easily assessed the neurological situation of a patient. Today I will delve into the conclusions we can draw when we see that a person is not able to walk heels. We usually observe two types of foot behaviors. It is possible that the patient is not able to lift the foot upwards at all. The other possibility, more frequent, is that you can lift your foot but, when supporting the heel, slap the floor. This case does not have enough strength to support the weight of the body and the foot falls to the ground.
Heel walking requires that several structures be healthy. In the mechanical part, the muscles that carry the foot upwards must function well. These muscles and tendons should be healthy to do the action. In addition the joint that they have to move, the ankle in this case, must be free without injuries or restrictions. Nor should there be other stops that limit mobility. The most frequent resistance that we find is the power of the twins as we will see later. On the other hand, there is the nervous system that has to send the signal to the muscles to make them move. If this signal does not arrive, it will do little to keep the mechanical part intact.
What muscles allow us to walk on heels?
The main muscle that performs the ankle dorsiflexion (lift the foot up) is the anterior tibial. Muscles called peroneal muscles that lead the foot outward are also important. Without the peroneos the foot would go inwards through the action of the twins who are very powerful. Finally there are the extensor muscles of the fingers and the big toe that help but are not essential for heel walking. As you can see, there are not many muscles but they must work well.
If a person cannot walk on heels first it is necessary to see that he does not have mechanical alterations like a rupture of the tendon or muscle for example. It seems obvious but this is important before thinking about a neurological injury. There are also diseases that affect the muscle, for example, although rare.
The nervous signal
The mechanical part is healthy and without limitations. Then we can only think that there is a neurological injury that does not let us walk on heels.
The nerve signal must reach the muscles to move the foot. For this, neurons and axons involved must be healthy. The signal begins in the motor cortex neurons. The motor cortex is a part of the brain where the voluntary command to move these muscles is born. Then the signal will go down the axons of these neurons. They travel the brain and spinal cord and reach the end of the marrow almost in the lower back. Here the axons will connect with the following neurons that will be in charge of leaving the column forming the nerve roots. The roots L4 and L5 will mainly be responsible for moving the foot up.
When the signal fails, the problem can be anywhere on this path that travels the entire body. There are many symptoms and signs that help doctors distinguish where the injury is. In a future post I will explain how a nerve injury that is in the brain or marrow of one in the leg is distinguished.
The resistance of the twins and the soleus
I want to comment on a frequent problem that has a solution if we realize it on time. The twins and the soleus are very powerful muscles that are responsible for flexing the ankle to tiptoe. They are the muscles that drive us when we jump and those that dampen when we land on the ground again. These muscles take the foot down and win by thrashing those who carry the foot up because they are much more powerful. What does this imply? It has several readings. Let’s put two examples that will make it very clear.
Imagine a herniated disc with L5 motor root injury. Due to the injury, the anterior tibial muscle loses the ability to move the foot upwards. The muscular size of the twins and soleus (those that flex the foot) is such that the simple basal tone of these muscles carry the foot downwards. This is so when walking and lying down for example. If we take an ever-falling foot posture down two things will limit the future of that foot. On the one hand, the length of the twins will be shortened (shortened by adaptation) and, on the other hand, adhesions will form at the ankle joint. Both will prevent the foot from moving upward, even if the nerve is fully recovered.
The other example I wanted to put is a back issue but it illustrates this very well. Imagine having a knee injury prevents us from supporting your foot for a long time. When walking with crutches we do not support the foot. If we have a passive attitude and do not move the foot, it will happen what we said before. The foot will be permanently flexed due to twins and gravity. After several weeks, when we want to move our feet again, we cannot see. I see daily that mobility is lost in the ankle and foot due to these circumstances that are often avoidable.