Shin splints

Shin splints is a general term used to refer to a painful condition in the shins.^[1] It is often caused by running or jumping, and may be very slow to heal. More formal medical terms include medial tibial syndrome,^[2] medial tibial stress syndrome^[3] and stress-related anterior lower leg pain.^[4] Some object to the classification of "shin splints" as a diagnosis, and instead consider it to be a symptom of other underlying conditions.^[5]

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Specific conditions

Overused muscle

One cause is overused muscle either an acute injury or DOMS (delayed-onset muscle soreness). The muscle pain is caused by any activity that involves running, jumping and sometimes even swimming. An individual not accustomed to running may experience pain in the shin muscles the next day even after a single, short bout of intense running.

Inflammation of connective tissue

Shin pain may also be the result of inflammation of connective tissue such as periosteum (periostitis). The pain may be caused by a stress fracture in the bone or some other problem like osteosarcoma. Pain in the lower leg may also be referred from a distant area of the body, such as pressure on the sciatic nerve (sciatica) which lies in the posterior thigh.

Chronic Compartment Syndrome

A problem which can mimic anterior shin splints is chronic compartment syndrome (CCS). This is a serious problem which can lead to significant loss of function in the lower leg. CCS occurs when swelling within the indistensible anterior compartment of the leg reduces blood flow. This relative lack of blood, ischemia, can cause more swelling and generate a positive feedback loop. In severe cases the result can be acute compartment syndrome (ACS) which requires emergency surgery to prevent ischemic muscle necrosis, muscle death due to lack of blood.

Diagnosis

Think of CCS when pain worsens steadily during exercise rather than improving as the ligaments and muscles warm. Tingling in the foot is a particular red flag; it indicates compression of the nerve.

If a bone problem is suspected to be causing inflammation of connective tissue, a bone scan can be useful in confirming the diagnosis.

Magnetic resonance imaging has been proposed as a diagnostic technique.^[6]

Causes

Most of these causes are contradicted by the MayoClinic's website, however, the purpose of the muscles of the anterior shin (tibialis anterior) is to dorsiflex the foot (raise the toe). It may not be obvious why a muscle which raises the toe can be stressed or injured by running, given that it is not responsible for propulsion. The reason is that unskilled runners overstride, and land heavily on the heel with each footstrike. When this happens, the forefoot rapidly slaps down to the ground. Effectively, the foot, which is dorsiflexed prior to making contact with the ground, is forcefully extended. This forceful extension of the toe causes a corresponding rapid stretch in the attached muscles. A reflex in the muscles responds, causing a powerful contraction. It is this eccentric contraction which leads to muscle soreness and possible injury to the muscle, tendon or connective tissue.

In a similar way, improper pronation of the foot during the footstrike can also cause pain in the muscles which oppose pronation, on the inside or outside of the shin. In proper pronation the foot strikes the ground on the outside of the heel and then rolls toward the inside of the foot approximately 5%. The ideal degree of pronation varies slightly with the individual. It is determined by factors such as the height of the arch (a higher arch has more clearance for pronation than a low arch) and the flexibility of the arch. In over pronation, the foot rolls in too far. The result is that the foot pushes off almost entirely from the big toe, causing excessive strain on the big toe and the outside of the shin. In contrast, under pronation occurs when the foot does not roll enough. This causes the entire weight of the foot strike to concentrate on too small an area on the outside of the foot, which places a corresponding strain on the shin.

It is also commonly believed that a contributing cause of shin muscle pain in some cases is the relative weakness of the muscles on the anterior of the lower leg compared to those in the calf. In this case, exercises that preferentially strengthen the anterior muscles may help alleviate or avoid shin splints. The shin pain is attributed to a forced extension of the muscle, in this case by the opposing calf muscles which "overpower" the shin.

Treatment and prognosis

CCS

If you suspect CCS seek medical attention before continuing to train. If you suspect ACS, seek medical attention immediately night or day.

Acute treatment

The immediate treatment for shin splints is rest. Running and other strenuous lower limb activities like football and other sports which include flexing the muscle, should be avoided until the pain subsides and is no longer elicited by activity. In conjunction with rest, anti-inflammatory treatments such as icing and drugs such as NSAIDs may be suggested by a doctor or athletic trainer, you can also take over-the-counter pain relievers such as Aspirin, though there is some controversy over their effectiveness. Some people will use acupuncture to treat shin splints though there has not been any conclusive or comprehensive study in the effects of acupuncture on shin splints.

Prevention

Training

Like any muscle, the muscles of the anterior shin can be trained for greater static and dynamic flexibility through adaptation, which will diminish the contracting reflex, and allow the muscles to handle the rapid stretch. The key to this is to stretch the shins regularly. However, static stretching might not be enough. To adapt a muscle to rapid, eccentric contraction, it has to acquire greater dynamic flexibility as well. One way to work on the dynamic flexibility of the anterior shin is to subject it to exaggerated stress, in a controlled way, such as walking on the heels. If the muscle is regularly subject to an even greater dynamic, eccentric contraction than during the intended exercise, it will become more capable of handling the ordinary amount of stress. Experienced long-distance runners practice controlled downhill running as a part of training, which places greater eccentric loads on the quadriceps as well as on the shins. A professional trainer, sport scientist, or doctor, should be consulted before engaging in this type of training.

Nutrition

Although typically proper nutrition is associated with other types of injuries (stress fractures particularly), shin splints can be greatly improved with a few simple dietary changes. One thing that will help to build strong and durable shins is proper intake of calcium. The shin can build itself to be stronger with the right amount of calcium. The second part is getting plenty of protein. Protein will help to prevent muscle related pain. The muscle cannot build itself without protein. Therefore training is not beneficial if there is not enough protein to rebuild the muscle.

Form

The long-term remedy for muscle-related pain in the shin is a change in the running style to eliminate the overstriding and heavy heel strike.

Most competitive runners do not strike the ground heel first. Sprinting is performed on the toes, as is middle-distance running. In long-distance running, the footstrike should be flat, though some elite long-distance runners will retain their forefoot strike acquired from years of competing in track-and-field.

Correcting the footstrike begins with posture: a haunched forward posture leads to a heel strike.

In both postures, the centre of gravity is directly over the foot. Physics requires this, because it is the condition that prevents a body from falling over. An object falls over when its centre of gravity shifts too far one way or the other outside of the range of its supporting base. Arching the back shifts the body's centre of gravity towards the rear, so that the legs must tilt forwards to compensate; shifting the weight towards the ball of the foot, and to the toes. Bending forwards at the waist has the opposite effect: the legs tilt backwards at the ankle, shifting the weight towards the heels.

During running, the centre of gravity changes dynamically. Because for most of the running cycle a drive leg extends backwards, the torso appears to tilt forwards to compensate for this. This forward tilt is similar to what happens in a standing position when one leg is raised from the ground and extended backwards. Inexperienced runners observe this forward tilt in professional athletes and attempt to imitate it by bending at the waist, which isn't the same thing. In the forwards tilt, the torso and extended leg still form a straight line; or even a slight backwards curve:

Footwear

Stress on the shin muscles can also be somewhat alleviated by footwear and choice of surface. Runners who strike heavily with the heel should look for shoes which provide ample rearfoot cushioning. Such shoes may be referred to as "stability" or "motion control" shoes. The so-called "neutral" shoes for bio-mechanically efficient runners may not have adequate support in the heel, because the runners for whom these shoes are intended do not require it. When their cushioning capability degrades, the shoes should be replaced. The commonly recommended replacement interval for shoes is 500 miles (800 kilometres). Excessive pronation can be reduced by extra supports under the arch. Running shoes which have a significant supporting bump under the arch are called "motion control" shoes, because they work by limiting the pronating motion. Also shoes with cushion shock features and shoe inserts can help prevent future problems.

In one study, use of an orthosis did not measurably improve recovery.^[7]

References