A Literature Review done for my Masters in Sports Medicine (MsSpMed), University of Queensland, Australia 2017

• Introduction
• Results
• Discussion
• Risk Factors
• Foot Pronation and Gait Analysis
• Body Mass Index
• Previous Injuries
• Potential Weaknesses
• Study Populations
• Under-reporting of Cases
• Cause or Effect
• Recommendations
• Future Studies
• Current Practice
• Conclusion
• References

Introduction

Running is gaining popularity among people looking at engaging in a healthy lifestyle. In 2014, Running USA reported that an estimated 550, 637 runners finished a marathon in the USA alone, which is a 255% increase from 198013.

With running being weight bearing, it is not surprising that 37% to 57% of recreational runners experience an injury over one year14. And of these overuse injuries, Medial Tibial Stress Syndrome (MTSS), has been reported as being the most12 frequently diagnosed injury in the Sports Physician’s clinic with incidence rates reported to be as high as 35%8 among runners. As such, much focus has been placed on this injury in Sports Medicine research.

The pathophysiology of MTSS is controversial. Some authors suggest that it is due to inflammation of the periosteum due to excessive traction  while others believe it is a bone stress reaction which can ultimately lead to a stress fracture26, 27, 28. However in both conditions – MTSS and tibial stress fracture, the commonest site of injury is both along the medial border of the tibia, suggesting that MTSS is ultimately a milder form of expression of stress on the tibia while a stress fracture would be the more severe form29.

Recovery from this injury is known to take weeks to months depending on its severity and the most effective treatment for MTSS is considered to be rest17. This disrupts athletes’ training programs and may impact their performance. As such, it is essential for Sports Physicians and our Allied Health colleagues to identify and understand modifiable risk factors of MTSS as they will form a pre-requisite in developing prevention and rehabilitation programs.

The goal of this literature review is to identify the key risk factors of MTSS and to make recommendations for future research into this area.

Results

A literature search was done on Pub Med to identify studies which discussed the risk factors of MTSS. Studies done on military personnel have been omitted because training in the military is vastly different from recreational running training. For example, military training involves carrying heavy loads, while running focuses on carrying as little weight as possible during runs.

The results are summarised in Table 1.

Discussion

This discussion will begin by discussing the key risk factors individually and their limitations. Thereafter, weaknesses in the studies reviewed which should be taken into account by future studies, will be highlighted.

Risk Factors

Foot Pronation and Gait Analysis

Pronation of the foot is the most studied risk factor for the cause of MTSS as this is possibly a risk factor that can be addressed easily through the use of orthotics. Both static and dynamic assessments have been used in these studies but both have their limitations.

The most commonly used static assessment method is the navicular drop test, which is utilised in studies by Bennett et al.2,4 Despite being a test that is commonly used, there is no standard definition of an abnormal navicular drop3, 20, 21, 22, and that normal values have been reported to range widely from 3.0 – 9.5mm in healthy subjects. In addition, the navicular drop test and other forms of static visual assessment have not been conclusively shown to have a strong relationship to dynamic foot function when a person runs.

In an attempt to overcome the limitations of static assessments, Willems et al.7 used 3D kinematics and footscan pressure plates to detect foot pronation and other variables such as pronation velocity and supinating angle when running. This method however requires highly scientific equipment which not all research facilities may have ready assess to.

Even though dynamic assessments may appear more specific than static assessments in assessing dynamic changes in the foot while running, it is still unknown if there is a difference between the two6. Furthermore, several studies of biomechanical measures of pronation and corresponding injury risk have not been promising23,24,25.

As such, further research is necessary in this area to elucidate the differences between the foot assessment methods and their effectiveness in predicting true dynamic foot function. Even so, more studies need to be done to ascertain pronation as a risk factor for MTSS.

It may also be possible that in running, the ankle, knee and hip joints are able to compensate for abnormalities such as pronation in the foot, resulting in a proper but compensated alignment. Abnormalities will then surface through gait analysis such as that being done by Tweed et al.11 which found that runners with an propulsive gait are at a much higher risk of developing MTSS. Gait analysis may therefore be more holistic than just looking at foot pronation.

Body Mass Index

BMI has been found to be a risk factor for MTSS, possibly because in a heavier runner, the tibia is exposed to more impact and force with each step taken in a run. Two studies3,8 found that an increased BMI is a risk factor for MTSS studied high school runners. But runners in most high school running teams have a low-normal to normal BMI and this is likely due to natural selection among the school population. With running being a weight bearing sport, faster runners who have a lower BMI will be drafted into the team. The challenge then is to compare the BMI among injured and uninjured runners, both of which are likely to have BMI which are already in the normal range of 18.5 – 24.9. For example, Yagi et al.8 found that uninjured runners had a BMI of 18.4 ±1.3 and runners with MTSS had BMI of 19.3±1.5. Erroneous interpretations of such results may lead to unhealthy motivations towards weight loss among runners who already have a BMI within the normal range, especially in females among whom disordered eating has been reported to have a prevalence of 16% to 47%30.

More studies need to be done to ascertain if a difference in BMI within the normal healthy range, can truly increase the risk of MTSS, to avoid unhealthy practices among athletes to lose weight. In addition, future studies should utilise direct measurement of height and weight of the participants and not rely on self-reported data3.

Previous Injuries

Perhaps the strongest risk factor for the development of MTSS is having a previous shin injury. Several studies3,4,6,9 have found that runners with a previous injury history in the shin or elsewhere in the lower limb have a higher risk for MTSS. This is likely due to resultant weakness in scar tissue around the injured area which increases the risk of re-injury.

This means that emphasis should be placed on sports medicine health care providers to elucidate such history, so that efforts can be made to tailor the athlete’s training program to allow a more progressive training program for musculoskeletal adaptation to prevent re-injury.

Potential Weaknesses

Study Populations

Many of the studies studied high school runners which range from 13- 17 years old. However, for the first 2 decades of life, the human skeleton grows in both size and density, with more growth occurring at the limbs than the trunk prior to puberty15. Due to its dynamic nature, different children who may be of the same age may also be at a different stage of bone growth. It is thus possible that children who may be at an earlier stage of bone growth may be more predisposed to overuse and repetitive injuries such as MTSS, and therefore act as a confounder in these studies. To address this confounder, it would be necessary to quantify bone growth using bone density scans which unfortunately are unreliable for children15, making this impossible. In view of this, it would be ideal to carry out studies on collegiate or post collegiate adult runners.

Under-reporting of Cases

Self-reported shin pain was used as a form of diagnosis in several studies even in high school children. This has several limitations. Firstly, it has been found that as much as 70% of patients who developed MTSS do not seek medical assistance22, suggesting that there could be severe underreporting using this method of diagnosis. Secondly, this may also lead to results being influenced by reporting bias as females are more likely to report injuries as they were more concerned about how the injury would influence their health at a future point as compared to males19.

Diagnosing MTSS in patients with a bone scan or MRI would strengthen the methodology but will come at a higher cost.

Cause or Effect

Due to the retrospective nature of some studies, it is not possible to ascertain if the findings are causing MTSS or vice versa.

For example, Madaley et al.5 found that the mean number of heel raise repetitions performed by participants with MTSS was significantly less than the reference group, suggesting that athletes with MTSS have endurance deficits of the ankle joint plantar flexor muscles. However, due to the study’s retrospective nature, it was not possible to establish any causal relationship between the two. It could be possible that due to the pain secondary to MTSS, participants were less active than controls leading to possible reduction in muscle  endurance as compared to the controls. This may also explain why Bennett et al.4 found no difference between the injured and uninjured runners as the heel raise test in a cohort study.

With regards to pronation as a risk factor, Bennett et al.2 assessed for pronation after the incidence of injury. However, as suggested by Yagi et al.8, pronation could be an effect of MTSS whereby muscles such as the posterior tibialis may have been inhibited secondary to the injury, leading to apparent pronation indicated by a navicular drop.

Thus, to overcome this, a cohort study should be done to investigate on the risk factors of MTSS.

Recommendations

Future Studies

As running is a highly dynamic activity, it is difficult to accurately and precisely measure biomechanical variables such as pronation and gait. As such, it is difficult to draw accurate conclusions from the current studies on this aspect. More research has to go into the development of 3D dynamic imaging to allow accurate assessments of these factors.

There is also a significant lack of studies that investigate training factors that may have led to the development of MTSS. Only Wen et al.9 attempted to address this and found that subjects who engaged in more high intensity interval training had a higher risk of developing MTSS. As described by Meeuwisse32 extrinsic factors such as training parameters, act on a predisposed intrinsic makeup such as “altered” alignment to result in injuries. In this multifactorial model, alignment issues such as pronation may be a risk factor for injury but its role may not be substantial in comparison with training practices such as mileage, intensity and stability of running habits, all of which may have the ability to enhance or compensate for the effects of this intrinsic risk factors. This is an area for future research exploration.

Current Practice

This review impacts my practice in 2 ways. In the screening of athletes, I will take extra precautions in patients with previous lower limb injuries and to highlight to the coach to ensure a more gentle progression in training load to avoid further injuries. In patients with newly diagnosed MTSS, I will adopt a wholistic approach. This includes assessing the patient’s gait and foot pronation to look out for obvious abnormalities that may require correction with orthotics. However, based on the patient’s history and severity of pronation, it may not be necessary to institute any intervention. In addition, I will also take into account training factors such as frequency and intensity and will work with the coach to adjust the training regime. With regards to patient advice, it is crucial not to give patients, especially females, who are already in the low-normal BMI range the wrong impression of their weight being a cause of their injury, to prevent unhealthy practices. This is a timely reminder for Sports Physicians and Allied Health colleagues to treat our patients holistically and to leave no stones unturned in the management of MTSS.

Conclusion

From this literature review, it appears that having a previous lower limb injury is the strongest risk factor in the development of MTSS. More quality research as well as development of assessment tools for biomechanical factors need to be carried out to draw further conclusions.

References

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