The Anatomy of Shin Splints in Runners

I am a firm believer the more you can educate yourself on your injury the better and more committed you will be to treating the condition. My opinion remains unchanged with shin splints or medial tibial stress syndrome.  The basis of understanding shin splints is knowing the anatomy of shin splints. 

In this section, I want to help you understand the anatomy relevant to shin splints.

The Bones Associated with Shin Splints

Bones form the basis of our body structure.  They serve many purposes including supporting the body, protecting organs, and most importantly helping the body move.  

There are 2 bones that make up the shin called the tibia and the fibula.  I will explain each separately in more detail.  They are pictured below:

1. The Fibula: 

The fibula is the smaller bone of the two that make up the shin.  It runs along the outside of your leg. This bone is a non-weight-bearing bone, meaning force from standing does not go through this bone.  

The purpose of the fibula is to join with the tibia in your ankle.  Together the tibia and the fibula create what is called the ankle mortise or the ankle joint.  At the ankle joint the fibula provides attachment points for the ligaments on the outside of the ankle. 

There are 8 muscles that originate from the fibula. These muscles serve to help move the foot.

2. The Tibia: 

The tibia is a bigger bone than the fibula.  It is the prominent bone located in the front of your shin.  

Unlike the fibula, the tibia is considered a weight-bearing bone.  In other words, the forces from standing go through this bone. 

At the end of the tibia, it combines with the fibula to create the ankle joint.  The tibia is the inside part of your ankle joint and provides attachment points for the ligaments to attach. 

There are 5 muscles that originate from the tibia. The muscles help move the ankle. 

The Muscles of the Shin Associated with Shin Splints

There are a total of 13 muscles that originate from both the fibula and tibia combined.  They all help to move the ankle, foot, and toes.  I won’t get into them all here as it is not the place, however, I will cover the ones that are important to shin splints. 

Muscles Associated with Posterior Shin Splints: 

1. The Calf: 

The Calf is made up of 2 muscles, the soleus, and the gastrocnemius.  The soleus is deeper with the gastroc coving the top of it.  These muscles run down the back of the leg and combine at the Achilles tendon which inserts on the heel.  These muscles are used to push the foot down.  Combined they are the primary muscles that propel you while running, sprinting, and jumping. 

2. The Flexor Digitorum Longus: 

This muscle starts at on the back of the tibia and runs down to all the toes beside the big toe.  This muscle is deep in the back of you leg hiding underneath the calve muscles.  It can not be touched.  Its purpose is to bend these toes toward the ground.  

While running this muscle probably the least important listed.  That being said the flexor digitorum longus is used during the push-off phase of running as the toes bend down towards the ground to push off and propel the body forward. 

3. The Posterior Tibialis: 

The posterior tibialis muscle also attaches to the back of the tibia.  It is a deep muscle meaning that it can not be felt as it is underneath your calf muscles. This muscle runs down the back of the leg and crosses behind the middle of your ankle.  From here it passes underneath the arch of your foot and attaches to the bottom of the foot.  

This muscle is crucial for stabilization fo the arch of the foot.  Often times flat feet or hyperpronated feet can be fixed by strengthening the posterior tibialis muscle. It also acts to press the foot down and inward.  

As you can imagine this muscle is extremely important during running. This muscle is used during the push-off phase of the running cycle to propel you forward.  It is also used during the landing phase of running as it helps distribute force through the arch of the foot.  It also acts to stabilize the arch during the landing phase as well. 

4. The Tibialis Anterior: 

The Tibialis Anterior runs along the outside of the tibia and across the front of the ankle.  It can be felt by placing your finger on the shin bone and sliding it to the outside.  The first muscle you hit while doing this is the tibialis anterior.  

This muscle is responsible for lifting your foot up or bringing your toes up toward your shin.  This is an important movement for running.  During the “swing” phase of running, you have to pull your toes up to allow your toes to clear the ground and to land on your heel properly. 

Putting it All Together: Anatomy of Shin Splints

According to the research, there are 3 anatomical areas of concern for shin splints. The first listed is considered anterior shin splints and the last two mentioned are considered posterior shin splints. 

1. The front/outside of the tibia just to the inside of the anterior tibialis muscle.  This can either be caused by the breakdown of the bone due to or tendonitis of the anterior tibialis both due to overuse.  Once again an injury to this area is considered anterior shin splints. 

2. Located at the lower 2/3rd of the tibia on the inside border. It occurs just before the bone attaches to the muscle.  

This injury is classified as an overuse injury of the bone. In short, the bone is not given enough time to recover or is underprepared for the relative forces of running causing microdamage leading to pain. 

It is hypothesized this pain is caused due to the pulling of the contracting anterior tibialis muscle.  This causes what’s called periostitis or chronic inflammation of the connective tissue that surrounds the bone. This chronic inflammation causes posterior shin splints.

3. Shin splints can also occur is just slightly more toward the inside of the second location.  This is where the muscles in the back of the shin are located.  These muscles are the soleus, the flexor digitorum longus, and the posterior tibialis, all of which I talked about above

It is hypothesized in the research the pain is caused by the repetitive pulling of these muscles of the back of the shin causing traction on the back of the tibia resulting in periostitis finally causing bone microtrauma.  This microtrauma of on the back of the tibia causes posterior shin splints. 

Conclusion

With this article, I hope you have a better understanding of shin splints anatomy.  The goal of this article was to help you educate and understand what shin splints are and how they are caused in a runner.  We reviewed the bones associated with shin splints along with the muscles associated with shin splints.