“Shin splints” is a vague term, used to refer to pain in the lower part of the shin bone. It is vague because pain on the shin can mean pain on the outside of the leg, inside of the leg, pain from a stress fracture,  or pain from compartment syndrome. The medical term for shin splints is Medial Tibial Stress Syndrome (MTSS). This term is accurate as it explains that the pain and discomfort is located on the inside of the tibia and is related to stress on the bone. Classic symptoms of MTSS are pain and discomfort in the lower leg/shin from repetitive running on hard surfaces, or excessive use of the foot flexors. The pain is debilitating enough to prevent the athlete from weight bearing activities, such as running, jumping, and dancing.

Clinical signs include increased tenderness and bumps on the inside of the tibia. Symptoms include dull aching pain induced by exercise and relieved by rest. Typical leg posture involves the heel bone turning outward excessively (over-pronation), and the knee turning inward. Clinical assessment shows weakness in the hip muscles and knee stiffness.

Studies show that shin splints are common among athletes who perform zig-zag hopping, basketball rebounding, staircase jumping, high impact exercises, and muscle fatigue. All the above-mentioned activities induce enormous strain on the shin bone. The contraction of the muscles during these activities alter the shin bone, which will be explained later.

Studies show that the cause of shin splints is a traction injury. To understand this, a brief anatomy discussion is needed. The deep calf muscle called the soleus, and another muscle called the flexor digitorum longus, are the two muscles which attach to the lower part of the shin bone, via a fascia (Tibial fascia), and their tendons cross the ankle to attach to the foot. Hence, as the above-mentioned muscles contract, this creates tension on the tibial fascia. The tensile force pulls on the fascia, resulting in the fascia pulling on the outer layer of the shin bone. The shin bone then reacts to the repetitive irritation by creating more bone, called remodeling. The process of remodeling is the removal of part of the bone that is not strong enough, and replacing it with stronger bone to cope with the increased demand. This explains the bumpy feeling on the shin bone during assessment. Moreover, if the stress on the weak bone continues, a stress fracture can result. Thus, a strong calf muscle stresses the shin bone just as a taut bow string stresses a bow.

Another way shin splints occur is through the ability of the shin bone to resist bending. Compression load on the shin bone increases from walking to running. The compression load during walking deforms the bone prior to the toes coming off the ground. Running uphill and zigzag running increase the compressive load three times higher than walking. The load is higher during sprinting and downhill running. The shear strain in the shin bone is high enough to produce shin splints. This is important in athletes who have poor running techniques. When the heel hits the ground during running, and when the body is going over the planted foot, stiffness in the knee decreases the shock absorbing effect. Studies show that stiffness in the knee is positively correlated with an inability to absorb shock. The bending of the knee when the heel hits the ground, and when the body travels over the foot during running, decreases stress on the shin bone. However, during a vertical jump, the compression load is lower than running, because the potential energy is dissipated by increasing the range of motion of the knee, hip, and ankle joints, and not transmitting energy to the shin bone.

Muscle fatigue is shown to influence the cause of shin splints. Muscles in the area of the shin and foot are supposed to act as shock absorbers by absorbing the stress of movement that would otherwise transfer to the bone. Hence, when athletes are doing too much too soon, it causes muscle fatigue, resulting in a decrease in the shock absorbing function of the muscle. Consequently, the stresses are transmitted to the bone, leading to shin splints. Furthermore, muscle fatigue increases the compression and tensile stresses on the shin bone by 26 to 35 percent. The damage accumulates more rapidly in the compressive area of the bone. A lack of endurance in the ankle muscles is evidenced in patients suffering from shin splints.

Hip adduction (knee turns in), rear-foot eversion (over-pronation- heel turns out), and free moment (the rotation load on the tibia)are the most important variables in predicting shin splints and stress fractures.

Treatment of shin splints is dependent on its cause. Active rest, ice, and elevation are common treatment techniques. Active rest allows time for healing and inflammation to settle. Athletes can maintain their fitness by using other forms of training, such as swimming or cycling. Avoiding weight-bearing exercises is strongly recommended. Ice and elevation decrease inflammation and pain. Taping the shin helps decrease the tension on the soleus and flexor digitorum muscles, allowing remodeling of the bone to take place. Stretching all the tight muscles around the ankle and shin bone increases the ability of the muscles to absorb shock, except soleus and flexor digitorum muscle. Stretching the soleus and flexor digitorum muscles increases the traction stress on the shin bone, making the problem worse.

The hip controls the function of the knee. The knee has to bend enough to facilitate the shock absorbing effect. The knee also controls the function of the ankle. Therefore, eccentric (negative) strengthening of the muscles of the ankle, knee, and hip is paramount in the treatment of shin splints, to control the lowering of the body on the involved leg.  Strengthening these muscles influences the bone to resist the bending effect during walking and running.

Correcting biomechanical defects, such as over-pronated foot and leg length inequality, are essential to correct running techniques. Practicing good running skills is important in encouraging the shock absorbing effect, resisting bone bending, and the proper function/control of the hips, knees and ankles.

There is no evidence that supports any single method for preventing shin splints. However, the most promising outcomes support the use of shock absorbing insoles. Other prevention methods for shin splints, based on the above understanding, involve wearing good fitting running/walking shoes with a hard heel-counter to control the heel bone during heel strike. 

Furthermore, athletes should balance running on hard surfaces with soft surfaces to decrease the repetitive bending effect on the bone. Studies found that shock waves generated during running were dependent of the surface. Grass surface resulted in a 25% higher shock wave than asphalt. Artificial track is 5% higher than asphalt. Natural grass provokes lighter loads on the heel and the ball of the foot.

Increase mileage gradually to prevent muscle fatigue. Muscles, as seen above, lower the bending stress on the bone and attenuate the load on the body. Fatigue diminishes the ability to dissipate and attenuate load on the body during running.

Strengthening the leg muscles is important to attenuate the shock wave propagated during running. Weakness in the eccentric contraction, such as running downhill, reduces the muscle ability to attenuate the shock wave during running.  The eccentric strength prevents knee stiffness, hence allowing  the knee to bend enough to dissipate the force away from the tibia and into the muscles. Hip abductors (muscles on the outer side of the hip) and gluteal muscle (butt muscles) strengthening prevents the knee from turning in, keeps the tibia in good alignment, and prevents the arch from collapsing. It also controls the free moment of the tibia, hence preventing the toes from turning in or out.

Stretching the leg muscles is also paramount in preventing shin splints. It increases the ability of the muscles to absorb shock waves.

Learning and practicing to run softer will decrease the tibial shock wave. Altering the frequency of the running steps will decrease the load on the tibia.

by Raj Issuree, MPT

Call STARS if you have questions on shin splints or need treatment.

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