Medial Tibial Stress Syndrome (MTSS) or what most of us call "shin splints" is a musculoskeletal overuse injury that produces generalized pain along the inside bottom two-thirds of the shin bone (tibia). It is different from other injuries such as stress fractures, tendonopathies and compartment syndrome that affect the tibia. Classified as an overuse injury, shin splints are common to runners but can also be present in other populations, often affecting beginner runners and those getting back into shape the most.
So what exactly is going-on to cause shin splints?
There is no conclusive explanation as to what actually occurs to cause the condition but there are a couple of different theories. Some of the muscles that are part of the calf and ankle have attachment points along the tibia (shin bone) - due to either excessive motion, muscle tightness or muscle weakness the muscles pull at the attachment points on the bone. Some believe this causes irritation or inflammation to the periosteum (thin layer of tissue that surrounds the bone) and others believe that small tears occur at the muscle-bone interface. In runners this is often in response to an increase in training and is more common in those just taking up the sport. Whatever the exact science is that causes MTSS it causes a bone stress reaction by repetitive loads on the tibia through a bending force. This causes the bone to constantly be remodelled and redeveloped, a process that causes pain and inflammation.
In most injuries, those involving overuse anyway, there is a link between load placed on the tissues and pain development. If the load is too much for the tissue to manage or it has inadequate time to adapt to the load and recover then the tissues have a reactive response which involves pain. But if you can reduce the load on the injured tissue to a manageable level this will often decrease the symptoms and allow the tissue time to adapt.
Those affected typically complain of pain at the beginning of an activity that subsides with warm-up but that reoccurs near the end of activity. Often pain reduces a few minutes with rest. And the pain typically can be re-elicited by applying direct pressure to the affected area.
The best method to avoid injury is by gradually increasing the load placed on your tissues allowing your body time for adaptation.
Potential Causes & Their Treatments
Cause: Too much load causing a bone stress reaction
Treatment Goal: Reduce the Load Placed on the Shin Bone
Overuse - too much, too soon - with athletes excessive mileage or training volume, change in exercise surface or increase in exercise intensity can cause too much load. You must give your body time to adapt to new loads. The common rule of thumb is no more than 10% addition in training volume per week. Listen to your body and alter your training plan - that may mean full resting or cross training. Proceed with a graded return to running or jumping with rest days between high impact activities to allow the bone to recover. Load can also be altered by changing exercise surface - soft surfaces such as treadmills or trails may provide some relief. The same can be said for a work environment; a change in surface, footwear or job demand to quickly can be a cause for shin splints.
Footwear - Old footwear loses is ability to support the foot; when the midsole of a shoe starts to break down it’s not supporting and protecting your foot, or the rest of your body as well as it was when you first started running in them. The typical guideline for a running shoe is to replace it every 500 - 800 kilometres. When your shoe starts to feel dead like it has lost its spring, it's time for replacement. Also ensure that you have the correct footwear for your foot type and running style.
Altered Biomechanics - excessive pronation (arch collapse), high arches and leg length differences can all play a role in developing shin splints. Orthotics are a proven treatment plan - arch support often works well to offload the tibia. Orthotics may be helpful for excessive pronation by limiting the pronation and for rigid high arches by increasing the surface area under the foot.
Running Form - Running form will affect the impact placed on your legs. With ineffective running form greater stress is placed on certain structures. Change in running gait can alter the load placed on the shin: 1) Increase your cadence - the theory with increasing running cadence is to decrease overstriding, with the goal of landing closer to your centre of mass with your tibia right underneath of you are opposed to ahead of you, deceasing the load placed on the tibia. 2) Increase step width - this acts to move the load from the inner shin but keeping the tibia straighter especially if you have a narrow or cross-over gait to begin with.
Muscle Tightness - Tightness in the calf and ankle muscles can place extra stress on the shin bone. The calf muscles especially play an important role in shin pain; ankle dorsiflexion (movement of your toes towards your shin) is essential during ground contact, if the ankle is stiff it often increases the load on the tibia. Limited knee flexion (bending of your knee) also plays a role in protecting the shin - knee flexion is one of the main mechanisms for shock absorption.
Muscle Weakness - Your muscles need to be strong and have the endurance to absorb impact step after step. Rehab should involve restoring flexibility, strength and endurance of muscles to help reduce the load on the tibia.
Other treatment options include compression socks, taping and icing.