Abstract
Shin splints have been redefined as medial tibial stress syndrome (MTSS) and, broadly, is the diagnosis given to someone experiencing pain on the posteromedial side of her tibia. MTSS has been found to be caused by muscle pulling on the bone’s periosteum or by postural issues, causing excessive tension on the medial side of the tibia which causes periostitis or injury to the cortical bone. Risk factors shown to cause MTSS are orthotic use, increased navicular drop (excessive pronation), increased ankle plantarflexion range of motion (ROM), little running experience, history of MTSS, female gender, high body mass index (BMI), increased hip external rotation, ROM, and tight plantar flexors. Despite the wealth of knowledge on the risk factors associated with the condition, there is MTSS has never been assigned a specific injury type. Some have actually defined “four grades” of MTSS severity, (see figure1), however these have been disputed. Further research is needed to fully understand MTSS.
Background information
Traumatic injuries have been thoroughly studied and thus are fairly understood how and why they happen. Chronic injuries are much less understood; therefore, there is much more debate surrounding how and why they happen. This is unfortunate because chronic injuries are common population-wide, but especially among those who do repetitive and strenuous exercise (Brenner 2007). Shin splints are the most common lower leg chronic injury that severely inhibits performance (Bramah, Preece, Gill, & Herrington 2018; Becker et al. 2017; Garnock, Witchalls, & Newman, 2018; Moen et al., 2012; Rathleff et al., 2011; Saeki et al., 2017; Sharma, Golby, Greeves & Spears 2011; Winters et al., 2017; Wright, Bliven & Bay, 2014; Yuskel et al.2011). “Shin splints” is an old term that explains a pain that occurs on the medial portion of the tibia (Bramah et al., 2018; Becker et al., 2017; Garnock et al., 2018; Moen et al., 2012; Rathleff et al., 2011; Saeki et al., 2017; Sharma et al., 2011; Winters et al., 2017; Wright et al., 2014; Yuskel et al. 2011). The new term, accepted by many, is medial tibial stress syndrome (MTSS). MTSS, commonly thought to be straightforward, lacks consensus on what causes it and how to diagnose it. Therefore, this literature review will highlight the debate on the cause and diagnosis of MTSS.
Introduction
Those who are physically active in anything involved with running, walking or jumping can experience injuries. Injuries often keep the physically active from continuing activity until recovery. One of the most plaguing injuries are medial tibial stress syndromes (MTSS), also known as shin splints (Bramah et al. 2018; Becker et al., 2017; Garnock et al., 2018; Moen et al., 2012; Rathleff et al., 2011; Saeki, Sharma et al., 2011; Winters et al., 2017; Wright et al., 2014; Yuskel et al. 2011). MTSS is a general name for an individual experiencing pain along the posteromedial part of the lower leg (Bramah et al., 2018; Becker et al., 2017; Garnock et al., 2018; Moen et al., 2012; Rathleff et al., 2011; Saeki et al., 2017; Sharma et al., 2011; Winters et al., 2017; Wright et al., 2014; Yuskel et al. 201). Although MTSS is accepted as a bone injury, one thing has not been ideptified as the singular cause of MTSS, nor has it been determined what type of bone injury MTSS is. (Bramah et al., 2018; Becker et al., 2017; Garnock et al., 2018; Moen et al., 2012; Rathleff et al., 2011; Saeki et al., 2017; Sharma et al., 2011; Winters et al., 2017; Wright et al., 2014; Yuskel et al. 2011). The lack of consensus on what causes MTSS also means there is no diagnostic criteria for MTSS (Burne et al., 2003). In turn, there is no consensus for the treatment of MTSS. In order to further the understanding of MTSS, studies were collected to find a consensus for the causes of MTSS and the diagnosing of MTSS.
There are nine possible causes of MTSS that have been studied (see table 1) (Garnock et al., 2018; Mattock et al., 2018; Steele, & Mickle, 2018; Schutte, Seerden, Venter, & Vanwanseele 2018; Willems et al., 2006; Wright et al., 2014). Other findings show potential to be causes of MTSS. For example, Bramah et al. 2018 found that contralateral pelvic drop (CPD) to be a possible cause for MTSS. These have been proven prospectively showing that those who have previously had MTSS are 10-32 times more likely to develop MTSS, and women are 4 times more likely to develop MTSS (Garnock et al. 2018). With this information a study predicted with an 80% accuracy if an individual had MTSS by a mere analysis of their hips (Garnock et al. 2018). Although it has been proven that these things are indicative MTSS, it is still debated how and why. The nine causes of MTSS seem to inflict one of three injuries which could possibly be defined as MTSS. The first injury is periostitis of the lower leg from tibial bony overload. Second, periostitis from plantar flexor muscle traction at muscle origin sites. Third, bone strains causing micro damage in the cortical bone which is exasperated by continuous strain to the bone resulting in fewer osteoblasts and more osteoclasts inhibiting bone healing, or in other words a stress fracture (Moen et al., 2012; Newman, Witchalls, Waddington, & Adams 2013; Winters et al., 2017). The causes for MTSS will be further investigated specifically with the kinetic chain and muscular effects on the tibia.
| Causes of MTSS |
| 1. Orthotic use
2. Increased navicular drop. (excessive pronation)
3. Increased ankle plantarflexion range of motion
4. Inexperienced running
5. History of MTSS
6. Female gender
7. High body mass index
8. Increased hip external rotation range of motion
9. Tight plantar flexors
|
| Table 1 |
Discussion
Before diving into the causes of MTSS, there was an additional challenge to work through. Many studies were done prospectively because it is not ethical to cause MTSS in individuals. Therefore, the studies had to watch athletes for up to 12 months and then record similarities or differences between the injured and uninjured. Many similarities and differences noted were within the kinetic chain from the hip down (Bramah et al., 2018; Bennell et al., 1996; Burne et al., 2003; Garnock et al., 2018; Mattock et al., 2018; Ozgurbuz et al., 2011; Sharma et al., 2011; Willems et al., 2006; Schutte, Seerden, Venter, & Vanwanseele, 2018; Yuskel et al. 2011) The kinetic chain, or how the joints work together from the hip down, affects where forces are being placed on the skeletal frame which can cause muscles or bones to compensate for force they are not made for or used to which causes injury. For example, increased hip internal rotation is a common connection disfunction that is associated with MTSS. Internal rotation at the hip is a main contributor to chronic rearfoot eversion (Bramah et al., 2018; Willems et al., 2006; Yuskel et al., 2011). Rearfoot eversion is an issue because it causes contributory over pronation in the foot which is found to be a main contributor to MTSS (Bramah et al., 2018; Willem et al., 2006; Yuskel et al., 2011; Naderi et al., 2018; Degens, & Sakinepoor 2018). With this knowledge researchers began to investigate why rearfoot eversion is causing MTSS.
Since most researchers accepted that rearfoot eversion is a contributing factor in causing MTSS, Becker et al. 2017 wanted to understand why. His results were rather controversial. He observed there were people with rearfoot eversion that generated no MTSS (Becker et al., 2017; Braham et al., 2018 Yuskel et al. 2011; Willem et al., 2006; Naderi et al., 2018). He hypothesized that it is not about the excursion or velocity of the rearfoot eversion, but rather the duration the individual stayed in eversion (Becker et al., 2017). It was found that there were no differences in ground reaction forces, but there was a longer duration of eversion (Becker et al., 2017; Naderi et al. 2018). Inversion needs to occur during the heel-off stage of gait to lock the talocrural joint to make a more stable foot. Following inversion, the foot goes into eversion allowing the foot to pronate to create a laxer foot for greater balance during mid-stance and terminal-stance. Becker et al. 2017 believes that because rearfoot eversion is lasting too long during mid-stance the foot is not in good balance requiring greater effort for muscles and other bones to stabilize the foot (Becker et al., 2017). Since other muscles are compensating for the forces it is causing strain and forces on the medial tibia which could be leading to MTSS (Becker et al., 2017).
To add to Becker’s et al. 2017 observations, Newman et al. 2013 also noticed issues with pronation being a risk factor. He also found that over-pronation and dorsiflexion are not predictors of MTSS for everyone. He observed that pronation and dorsiflexion were not causes of MTSS unless the over-pronation is greater than 10mm (Newman et al., 2013) A common preventative treatment for MTSS is the use of orthotics, but it was found with Newman that orthotics caused more issues with navicular drops, which were leading to greater number of occurrences of MTSS (Newman et al., 2013). This may mean orthotics are not a good preventative care for MTSS. However, it could be hypothesized that it is only preventative if foot posture is a risk factor, as presented by Bramah et al. 2018, Willem et al. 2006 and Yuskel et al. 2011 with rearfoot eversion. Putting all this together it can be determined that rearfoot eversion is a cause of MTSS because it causes over pronation, however this is only true if the eversion is causing pronation over 10mm or if the rearfoot pronation is not being corrected during mid-stance.
Another dysfunction in the kinetic chain that causes MTSS was researched by Bramah et al. 2018. Bramah et al. 2018 studied the effect of the kinetic chain on MTSS from the hip by analyzing contralateral drop (CPD). Contralateral drop of the hip is a common occurrence in those with weak hip abductors muscles like the gluteus medius. Bramah et al. 2018 wanted to see how this would affect gait and in in turn, how it could cause MTSS. He found that those experiencing CPD had a greater forward trunk lean and hip abduction during mid-stance of the gate. In this position it caused iliotibial band tension and lateral patella displacement which would put greater tension on the medial tibia (Bramah et al., 2018). After studying postural issues associated with MTSS, it seems dysfunctions with the hip, knee and foot could be the cause of MTSS, which may be defined as a bone injury associated with the cortical bone presented as a type of stress fracture or stress reaction (Mattock et al., 2018; Bennell et al., 1996; Burne et al., 2003; Newman et al. 2013).
Aside from kinetic chain dysfunctions, tension from the muscle onto insertion sites on tibia bone have been hypothesized to cause MTSS. Seven different studies investigated muscular strength and endurance and their possible effect on MTSS (Mattock et al., 2018; Bennell et al., 1996; Burne et al., 2003; Saeki et al., 2017). The risk for MTSS increased by four times for every centimeter decrease in calf girth (Mattock et al., 2018; Bennell et al., 1996). Bennell et al. 1996 hypothesized this occurs because as an individual runs the calf muscles must resist forward bending of the knee. Without adequate opposing force to counteract ground contact, it puts extra strain on the bone to attenuate the ground reaction forces (Bennell et al., 1996). However, MTSS still commonly occurs in those who have adequate calf girth. Mattock et al. 2018 hypothesized that reduced plantar flexor muscle endurance could be a cause for these stress reactions because of poor ground reaction force and attenuation.
Several studies support Mattock’s et al. 2018 hypothesis and blame the plantar flexor posterior tibialis (Becker et al., 2017; Rahtleff, Winters et al., 2017; Wright et al., 2014; Sharma et al., 2011). However, a study done by Saeki et al. 2017 showed that the flexor digitorum longus has more attachments to the tibia. He hypothesized that the flexor digitorum would cause more damage to the bone than the posterior tibialis (Saeki et al., 2017). With this theory Saeki et al. 2017 tested the strength of plantar flexors in injured athletes with MTSS against healthy athletes. He found that flexor hallicus longus activation was much higher in the first metatarsal verses the second through fifth. It was determined that this was occurring because the flexor halluces longus was compensating to take pressure off the flexor digitorum longus because of the possible injury it was causing the tibial (Saeki et al., 2017). Saeki et al. 2017 further observed greater rearfoot eversion with the feet that had the contributory flexor hallicus longus which is a common pathology for MTSS (Saeki et al., 2017). With these findings Saeki concluded that the flexor digitorum to be more of a concern for causing MTSS.
Buldt et al. 2018 had a similar study to Saeki but with different findings. He used a pressure plate to find the center of pressure (COP) under a foot during gait with someone with lower leg injury against a healthy individual. He found that during terminal stance the planus foot had less lateral-medial force than the normal foot. Since there is less later-medial force the force was being taken off the first metatarsal and transferred more laterally. In terminal stance the pressure needs to transfer to the first metatarsal to have optimal force production through the foot (Buldt et al., 2018). Since this is not happening, the chance of a lower leg injury is greater because the incorrect muscles are compensating to maintain gait and putting extra traction forces on muscle insertion sites causing periostitis (Buldt et al., 2018; Saeki et al., 2017). This means more blame is to be put on the flexor hallicus longus to be a cause for MTSS. From these different studies it can be confidently concluded that an imbalance of any plantar flexor is a risk factor for MTSS.
One reason to study what causes an injury is to find a diagnosis for an injury. Knowing what causes an injury allows a consensual decision on what the injury is. Unfortunately, there is no consensus on what causes MTSS, and therefore there is no consensus on how to diagnosis MTSS which means is no official consensus on the definition of what type of injury MTSS is. To help decide what type of injury MTSS is, research has been done to see what types of treatments help alleviate MTSS symptoms. Some common treatments for MTSS are stretching the calf, graded running, and compression (Moen et al., 2012). Moen et al. 2012 performed a prospective study to see if these treatments, which are all soft tissue treatments, had an affect on the recovery time of MTSS patients. None of the treatments had any effect on recovery time, which suggests that MTSS is not a muscular/tendinous injury. To counter this theory, Ozgurbuz et al. 2011 tested the bone mass density and found no difference between those with MTSS and the control group, suggesting it is not a bone injury. Ozgurbuz’s et al. 2011 findings are inconclusive because they are also counteracted by studies that have found that bone mass density was less in individuals with MTSS (Magnusson et al., 2001; Gmachowska et al., 2018). Consequently, no official diagnosis or treatment has been decided for MTSS.
Having counteracting studies has caused many practitioners to be confused on best care for MTSS. To help resolve the confusion Gmachowska et al. 2018 combined studies with his own research to create a diagnosis for MTSS and a definition. He took 44 individuals which in total had 53 tibiae presenting with symptoms of MTSS (Gmachowska et al., 2018). He took an MRI of each tibia and combined the results and classified the results of round injuries in the tibias into four grades (Gmachowska et al., 2018).
| Grade 1: | Bone marrow edema and periosteal edema |
| Grade 2: | Bone marrow and periosteal edema but more severe |
| Grade 3: | Bone marrow and periosteal edema but more severe |
| Grade 4: | Accelerated bone remodeling |
| Table 2 (Gmachowska et al., 2018) | |
The grades help to define the three hypothesized types of MTSS. Grades 1-3 are periostitis with some signs of stress reactions whereas grade 4 is indicative of a stress fracture. This may be why there is no official consensus on what MTSS is, because there are varying degrees. Although this looks like a good solution, other studies found similar MRI findings, but in athletes without symptoms of MTSS (Winters et al., 2017). Even with the contradiction this is a good start to creating a diagnosis for MTSS which will help find the best treatments for those suffering from MTSS.
Suggested Future Research
The studies mentioned discussed how posture, or muscles can put tension on the medial side of the tibia, but none measure the direct force being placed on the Tibia. One possible question to explore is, is there is a certain amount of force the tibia can take before breaking down, whether at the periosteum or cortical. Those with a high BMI are at a great risk for MTSS which may show that perhaps there is. A study that could be done is to measure the GRF of individuals at running and walking who are having symptoms of MTSS and those who are not. Alongside the GRF a measurement of the length of their tibia and whole leg should be taken. Lastly, they should be video recorded so the angle of the leg against the ground can be taken at initial contact, and terminal stance. With these measurements it should be possible to calculate the amount of force being placed on the tibia at varying lengths. The result of this study could show if certain amounts of forces on the tibia cause MTSS. If the results are not significant it could be done again but compared with the bone mass density of the individual tibias. Perhaps certain bone densities can only handle certain forces. With this information preventative treatment would to help correct posture or muscle strength to compensate for forces on the tibia or find if certain bone densities predispose individuals to MTSS and physical exercise needs to be implemented more slowly or cautionary.
Along with this idea of studying medial tibia forces, it would be wise to study functional movements and how it may cause MTSS. Every study found focused on the kinetic chain or muscles as the cause for MTSS, when it may just be a functional movement. Perhaps when an individual is running, and he/she is running with an extra long stride causing unusual forces on the lower leg. Several studies did mention fewer year of running experience as a risk factor for MTSS suggesting that the bone or muscles require some amount of adaptation before introducing them to enormous amounts of training. Even though the lack of running years was introduced as a risk factor, no study researched into why this is, or if this really is a risk factor. The point is more research is needed to understand how amount of training, or form of training could be affecting the risk for MTSS.
Conclusion
MTSS is defined generally as pain on the posteromedial portion of the tibia (Bramah et al., 2018; Becker et al., 2017; Garnock et al., 2018; Moen et al., 2012; Rathleff et al., 2011; Saeki et al., 2017; Sharma et al., 2011; Winters et al., 2017; Wright et al., 2014; Yuskel et al., 2011). The exact nature of the injury is debated in the literature, but has been narrowed down to three possibilities: periostitis due to repetitive contractions of the muscle causing injury to the underlying peritoneum at the site of origin, periostitis due to repetitive medial forces on the tibia, or injury to the cortical bone due to repetitive medial forces on the tibia (Moen et al., 2012; Newman et al., 2013; Winters et al., 2017). The three types have been further narrowed down under four grades of injury (see table 2). Under the theory that muscle is causing periostitis it was found that each plantar flexor to be a potential cause for MTSS (Becker et al., 2017; Rahtleff, Winters et al., 2017; Wright et al., 2014; Sharma et al., 2011; Saeki et al., 2017; Buldt et al., 2018). Periostitis was also caused by over-pronation during gait, typical from rearfoot eversion, because of the inverting forces placed on the tibia (Bramah et al., 2018; Willem et al., 2006; Yuskel et al., 2011; Naderi, Degens, & Sakinepoor, 2019). Stress fractures found in the cortical part of the bone was a common finding in several studies suggesting greater problems occurring than just periostitis which is causing the confusion in diagnosis (Moen et al., 2012; Newman, Witchalls, Waddington, & Adams, 2013; Winters et al., 2017). In conclusion, no diagnostic consensus has been found, and the actual cause for MTSS is muddled. Further studies specifically regarding forces placed on the tibia, and how functional movements affect MTSS will help solidify the cause of injury and help with finding the true nature of injury which will lead to a better ability to specify a diagnosis.
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