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Saturday, August 8, 2020

Shin Splint Discussion: Part II

This is Part II of a discussion on Shin Splints. The link to Part I is attached.

One of the number one causes of shin splints that do not seem to improve is undiagnosed stress fractures. The young inexperienced cross country runners (or other athletes) who are not responded to shin splint treatment should be worked up for tibial (anterior or medial shin splints) stress fractures or fibular (lateral shin splints) stress fractures. This is still a version of the same process of overload. The overload in shin splints goes to the weakest link in the chain: the bone and a fracture occurs, the periosteum of the bone (which is the classic shin splint), the muscle belly, or the tendon.

The five most common types of stress fractures which are mistaken for shin splints are: posterior tibial (posterior or medial shin splints), distal tibia (medial shin splints), anterior tibial (anterior shin splints), fibula (lateral shin splints), or proximal tibial (either medial or anterior shin splints). Of course, if you do make the diagnosis a stress fracture, always think about the overall bone health. Did this bone break not only due to the mechanical overload of hills, pronation, supination, tight muscles, etc, but is the bone actually healthy? An unhealthy bone becomes the weak link in the chain. 

I mentally use the Rule of 3 in overuse injuries. The Rule of 3 means look for at least 3 legitimate reasons why a certain structure started hurting. Overuse picks on the weakest link in the chain, and many times a structure is weak because of 3-5 factors working against it. For example, since we are talking about stress fractures, remember that 40 years ago they were thought only to be related to impact shock. Then, article after article came out regarding stress fractures related to muscle contraction or bony torque. And, recently, the role of overall bone health has been more publicized. Therefore, if we use the common example of lateral shin splints actually being undiagnosed fibular stress fractures, the common rule of 3 includes:

  • Inadequate bone health with eating problems or low Vitamin D

  • Excessive supination causing excessive peroneal strain or simply increased lateral body weight

  • Weak Peroneal Tendons increasing the strain or pull on the fibula

  • Old lateral ankle sprains increasing the supination moments of force

With shin splints, the game for me is trying to figure out what muscle group is involved and what could be the cause of the overuse of that muscle/tendon. If we take the extensors as a group, they give us anterior shin splints. What causes general overload of the extensor group? The extensor group is again overloaded with a very tight achilles tendon complex which makes it work  harder to flex the ankle joint. Also running hills makes you use the extensors differently than what you are used to, especially eccentrically as you run downhills as they avoid foot slap. Typically our bodies will get used to the activity, so shin splints are usually from new activities or changes in some routine. When shin splints occur in a seasoned runner for example, I think bone over tendon, therefore I want to rule out a stress fracture first. And, to add an extra twist, there are 4 individual extensor tendons. The anterior tibial tendon can cause a shin splint particularly if the foot pronates too much. The anterior tibial is straining to decelerate contact phase pronation. The peroneus tertius and extensor digitorum longus get painful with over supination especially in midstance or propulsion. While the extensor hallucis longus is fairly neutral to the subtalar joint, it can overload in functional hallux limitus as it tries to lift the big toe off the ground, or in painful big toe joints (perhaps hallux rigidus) as protection. 

The lateral shin splint syndrome is commonly caused by over firing of the peroneals to protect the lateral ankle. Common causes of normal lateral or foot overload are: laterally worn shoes, running on banked road (foot held supinated), shoes laterally unstable (70% of all supination problems are not in supinators structurally), and foot types like pes cavus that overly supinate. One of the exceptions to this concerns the function of peroneus longus tendon to raise the medial arch by plantar flexing the first metatarsal. Here lateral shin splints can develop from over pronation when the peroneus longus is strained. 

The posterior shin splint is typically the soleus fibers or a tibial stress fracture. The pain is deep to the calf muscle belly, so given the name shin splint since it does not seem to be a calf strain. The stress fracture may never show up on xray, and not seem serious enough to get a conclusive MRI or Tc99 bone scan. 

In Part III of our discussion on Shin Splints, I will talk about general mechanical treatments

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Thank you very much for leaving a comment. Due to my time restraints, some comments may not be answered.I will answer questions that I feel will help the community as a whole.. I can only answer medical questions in a general form. No specific answers can be given. Please consult a podiatrist, therapist, orthopedist, or sports medicine physician in your area for specific questions.