Shin splints, or medial tibial stress syndrome (MTSS), is a disabling, overuse injury caused by repetitive stress on the shinbone, characterized by the pain felt in the lower two-thirds of the shinbone. It is brought on by running or other activities that apply load on the lower extremity. It is also characterized by the inflammation of the periosteum, which is a membrane that covers the surface of all bones except that bone joints. Pain typically occurs during or after exercise. The inflammatory condition is called periostitis.
MTSS (shin splints) share common characteristics to stress fractures of the shinbone, as it is a stress-induced reaction. Knowledge about the aetiology and mechanism of development of MTSS, however, is still limited; there are debates on whether it is a completely separate disease to stress fractures of the shinbone. While they do share similarities, the fact that shin splints occur in areas on the shinbone where stress fractures are not found, and that not all MTSS cases eventually become stress fractures, are evidence used to justify viewing these two conditions as completely different entities.
In the early stages of MTSS, pain is usually brought on at the beginning of exercise but then subsides as the exercise routine progresses. If the exercise routine is long enough, pain may return. In the later stages, however, pain can be brought on by less activity and may even be felt when at rest. It has a prevalence of 4% to 35% in the athletic and military populations. The condition is mostly found in runners, accounting for 13.2 to 17.3% of all running-related injuries. It is also commonly seen in other sports such as basketball, football, and dancing.
Risk factors for shin splints may be categorized as extrinsic, intrinsic, historical and gender. Extrinsic factors include:
- The frequency and intensity of training
- The training surface.
Both factors affect how the load is applied on the lower extremities of the body.
- Increased Body Mass Index (BMI). This is possibly due to increased load bearing.
- Foot hyperpronation. Pronation is a natural reaction when walking or running, where the foot, flat on the ground, rolls inwards for stabilization. Hyperpronation, however, can put pressure on the medial or inner sections of the shinbone.
Historical risk factors include:
- Prior use of orthotics or shoe inserts – while there is a significantly correlation between prior use of orthotics and developing MTSS (in one meta-analysis, 25% of the patients that developed MTSS were previously prescribed orthotics), the mechanism is unclear
- History of shin splints – those with previous cases of MTSS have a significantly higher risk of recurrence cases. It has been suggested that this may be due to causal factors still being present, or that damage done persists long after. One study found evidence of failed bone healing in MTSS sufferers up to 8 years after MTSS injury.
- Fewer years spent actively participating in running – this is likely to be due to lower neuromuscular and bone adaptation to the sport, as the body is constantly conditioning itself based on present mechanical load demands. This may indicate a need for a preconditioning program, but further studies on recommended length of duration still needs to be done. One study did conclude that 4 weeks was insufficient for reducing injuries in runners.
- Overall, females are more at risk of developing shin splints than males – also, some risk factors are only specific to one gender, for example, lower fat intake, leg length discrepancy, and lower bone density were significant risk factors for females, but not considered risk factors for males.
The main symptom of shin splints is the pain brought on by exercise, but not present when at rest. While exercising, pain may subside, however, it can relapse later on in the session.
The diagnosis of shin splints is usually clinical, based on symptoms, observation, and palpation of the area. There may be localized tenderness between the middle and lower third of the shinbone and the patient may not recall any single event where injury could have taken place, indicating that it is likely to be a stress –induced overuse injury. For imaging, MRI is the preferred option due to its sensitivity and aid in detecting borderline characteristics such as periostitis.
Treatment of MTSS (shin splints) varies according to the cause and the injury, but is typically non-surgical, with rest, ice and supportive footwear most frequently prescribed. Recovery from MTSS tends to take several months. One study found that 90% of the subjects took over 6 months (about 250 to 300 days) to recover sufficiently to complete an 18-minute run. Patients with chronic MTSS may have to undergo surgery.
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