Medial Tibial Stress Syndrome (MTSS) is one of many overuse lower leg injuries found under the overall term of exercise-induced leg pain or shin splints[1]. Stress fractures, MTSS, and chronic compartment syndrome are the three most common forms of exercise "induced leg pain, with MTSS having the highest prevalence[2–4]. MTSS is an exercise-induced, localized pain along the distal two thirds of the posterior-medial tibia and can be a debilitating injury in runners. In studies of recreational runners, MTSS has been reported as the most or second most frequently diagnosed injury and specified 13.2%–17.3% of all running injuries [1–3].

Although the precise pathologic abnormality has not been identified, it appears to involve a stress reaction by the crural fascia (fasciitis) or bone along the posteromedial portion of the tibia most consistently associated with the insertion of soleus, and probably not the periosteum [5].

MTSS can be accurately diagnosed with a clinical history and physical examination [1–4]. Pain can be induced by exercise, last for several hours or days, without dysesthesia and reproduced upon firm palpation of the posterior medial border of the tibia. Imaging investigation like plain radiography, bone scan and MRI should be implemented in order to rule out other conditions such as a stress fracture. However, many studies indicated that some types of imaging have been associated with both false-positive and false-negative results, it has therefore been suggested that if the clinical picture showed MTSS and there is no diagnostic enigma, further images are not necessary [2].

A few studies have reported the injury rate and relationship between lower extremity alignment and MTSS among adolescent runners [6, 7]. Bennett et al have studied the relation of pronatory foot type using and MTSS. They mentioned that the combination of sex and navicular drop test measures provides an accurate prediction for development of MTSS [4]. In Plisky et al's study navicular drop has not been considered an appropriate measure to identify runners who may develop MTSS during a cross-country season [8]. In 2007, Reinking et al have studied intrinsic and extrinsic risk factors contributing Exercise-related Leg Pain (ERLP) in collegiate cross-country athletes [9]. The percentage of athletes with history of ERLP associated with running, the incidence of ERLP during one season, factors including years of collegiate running, training distance, and gender associated with ERLP and relationship between foot type and ERLP have been investigated. They concluded that ERLP history and season incidence was common among cross-country athletes and the only risk factor identified for season incidence of ERLP was a history of ERLP [9].

In 2004, Burne 'et al reported a 12-month prospective clinical study on biomechanical and anthropometric risk factors associated with Exertional Medial Tibial Pain (EMTP)[10]. They found that greater internal and external hip range of motion and lower lean calf girth as biomechanical factors were associated with male EMTP; however, the increased incidence of EMTP in women was without any identifiable risk factor [10].

Tweed et al investigated the relationship between functional and static foot posture and medial tibial stress syndrome in distance runners [11]. Variables identified as being significant predictors of medial tibial stress syndrome were the difference between the neutral and relaxed calcaneal stance positions, range of motion of the talocrural joint with the knee extended, early heel lift and abductory twist during gait, and apropulsive gait. They concluded that runners with suspected symptoms of MTSS should be assessed dynamically and statically for abnormal or mistimed pronation[11].

Most of the studies published to date have different results [4, 8]. On the other hand, some investigations have done on professional athletes [6, 9, 11]. Due to possible selected exclusion in persons with MTSS from professional competition, investigation on nonprofessional athletes may determine the effects of potential risk factors more accurately; therefore, we prospectively studied physical education students to determine potential risk factors for the development of MTSS. Considering that the development of MTSS is likely multifactorial, we also examined other risk factors such as gender, running experience, and body mass index (BMI).

This prospective study was conducted at Rajaii educational exercise training university in Tehran from September 2006 to January 2007. Our population included 66 nonprofessional athletes (educational exercise students) who were enrolled in track- and- field as a main course. Twenty-one male and 45 female (age 20 ± 1.5 years, BMI 21 ± 2 Kg/m² and height 1.68 ± .9 m) were studied. Subjects with a history of congenital deformity, surgery and traumatic injuries to either lower extremity in the previous 6 months were excluded. A session was held at university to distribute consent forms and give an overview of the research.

The measures were taken in the first 3 weeks of the semester. At the time of measurement, each subject signed consent form and the examiner completed a demographic data sheet that included name, sex, age, and number of competitive running years. The initial sample consisted of 68 runners, 21 men and 47 women, which provided 136 limbs. Two of runners were eliminated because of injury during the course. Data pertaining to past history of leg pain, injury or fracture, number of hours in physical activity per week, type of physical activity and associated diseases were collected in the questionnaire.

Static lower extremity measurements including intercondylar interval of femur, intermalleolar distance, Quadriceps angle, hip internal rotation angle, hip external rotation angle, tibiofemoral angle, tibial alignment, rear foot alignment or calcaneal (Achilles) angle, navicular drop test and length of lower limb were measured in every lower limb.

All angle measurements were taken using one goniometer and recorded. The measurements were taken 2 times and an average was calculated. On all subjects, the anatomical landmarks were drawn by a nontoxic ballpoint pen and erased after first set of measurements with an alcohol swab. Then several photos were taken from knee and ankle of limbs by a digital ixus 70 Canon camera (with 7.1 mega pixel resolutions). All photos were taken bare foot, in standing position, in specific distance and with constant angle in the same location [9, 10], then all photographs were analyzed in Photoshop software (version 7.0) for determination of angles in degrees.

All measurements and physical examinations had been performed by one physician (sport medicine specialist). All subjects were trained during educational track- and- field course and they were running, jumping, marching and circuit training 14 hours per week for 17 weeks. The location of training and surface of field was the same for all subjects and the shoes of all subjects were checked for appropriateness. All shoes were common runner type and no one used insole. After the training period (17 weeks), all subjects were examined for clinical sign and symptoms of MTSS. The diagnostic criteria of MTSS included:

Pain history: pain was induced by exercise and lasted for a few hours or days after exercise, located on the posteromedial border of the tibia, no history of paresthesia or other neurovascular symptoms indicative of other causes of leg pain

Location: Over an area minimum of 5 cm, along the posteromedial border of the tibia.

Palpation: Palpation of the posteromedial border of the tibia produced pain that was diffuse in nature and confined to the posteriomedial border of the tibia [2, 12].

Runners who reported a previous running pain and injury were over 2 times more likely to incur an MTSS, but the association was not statistically significant. Odds ratio & 95% CI were used to establish if the descriptive data could accurately predict the development of MTSS (odds ratio [OR], 2.18; 95% CI: 0.7, 6.4), with similar reports among girls and boys. The small size of study may account for lack of this association.

In this study the relationship between MTSS and ND was significant, in accordance with Bennett study [4]. Average navicular drop has been reported from 3.0 to 9.5 mm in healthy subjects with the average navicular drop observed in runners with MTSS in this study was 6.8 to 8.9 mm. The mean (± SD) values for right and left navicular drop in our study (5.14 ± 1.2 and 5 ± 1.5 mm for noninjured runners and 6.08 ± 1.553 and 6.46 ± 2.1 mm for runners who developed MTSS, respectively) were not generally higher than previously reported values.

However this finding differs from the study conducted by Plisky et al, who found no association between navicular drop and MTSS in competitive adolescent runners [8]. The discrepancy in findings, may be due to differences in the specific measurement technique [2, 4, 17]. The Plisky study used the method assessing navicular drop advocated by Menz and others, whereas we used the method described by Sell and Picciano [19, 20].

Our incidence estimates of MTSS for the overall sample (19.7%) and girls (22.2%) were not similar to Bennett et al, with incidence estimates of 12% and 19.1%, respectively. The frequency of MTSS assessed in our study was not significantly different between girls and boys (22.2% versus 14.3%). While others have suggested the higher incidence of injury in women rather than men [2, 4, 10, 22], we did not find this issue in our study, however, the frequency of sport activity was nearly the same in both gender. We did not find apparent relationship between lower extremity alignment and MTSS that was consistent with some similar studies [23, 24].

Likewise, no significant difference in the rearfoot or calcaneal angle was found between the injured and noninjured groups, contrary to the findings of Viitasalo and Kvist [25].

Considering that eversion is the frontal plane component of subtalar pronation, we expected to find a significant difference between the injured and noninjured groups in rearfoot or calcaneal angle like we found in the navicular drop test. The apparent conflict between the navicular drop test results and the rearfoot or calcaneal angle results may be explained by our use of uniplanar measurements of a triplanar motion (static assessment of a dynamic issue) [13, 26].

Moreover, excessive pronation is connected with overused problems of lower leg, in the view of James et al [27] it is a compensatory motion secondary to anatomical misalignment of the heel-foot or leg-foot.

The increased pronation of the subtalar joint may be due to forefoot varus deformity, a rear foot varus deformity, functional equinus and tibial varum. As a conclusion, they pointed out that no single anatomical variation correlated with any specific diagnosis [26]. Therefore, the discrepancy between the result of ND and calcaneal angle in our study may be due to not considering forefoot varus deformity measurement.

According to Tiberio, an increased Q-angle, excessive foot pronation, increased femoral anteversion, and weaker quadriceps together may cause leg pain [28]. In our study, there was no significant difference between Q-angle in MTSS group versus uninjured, so Q-angle may not have a role in contributing MTSS.

We did not find an apparent difference between the injured and noninjured limbs in tibial alignment, comparable to Bennett study [4], but it was in conflict with Tomaros' research [29]. In this study the difference in tibiofibular varum between the injured and uninjured extremities may be one example of an asymmetry that can cause unilateral overuse symptoms [29].

Although runners with MTSS had a little higher BMI, the difference was not significant. So other studies in military recruits had mentioned that BMI remains an equivocal risk factor for any type of lower extremity injury and in the study by Plisky higher BMI was associated with risk of MTSS in runners. In our study, subjects were divided into higher and lower subgroups based on their BMI (> or = 21 and < 21, respectively), then correlational analysis were performed. However, no relationship was found between MTSS and BMI of the participants (Odds ratio [OR] = 0.79; 95%CI: 0.2, 2.68).

Runners who reported a previous running injury were over 2 times more likely to incur MTSS, but the association was not statistically significant (odds ratio [OR], 2.18; 95% CI: 0.7, 6.4) with similar reports among girls and boys. Other researchers have reported an association between prior injury and current injury [5, 9, 30]. As the small number of MTSS cases observed likely accounted for the statistical finding, it should be suggested that prior injury may play a role in the occurrence of MTSS and warrants further investigation.

In our study some of the subjects had a previous history of anterior leg pain; meanwhile the students were excluded if they had a history of lower limb injury during the previous six months. Hence, there may have been subjects who had an older or less recent history of pain, but did not develop MTSS in the study period. It should be considered as a reason why we may have not found an association.

The main limitation of this study is the small sample size that reduced the power of our analysis, so further studies in larger groups are required.

This research is a prospective study in athletic population and we have highlighted the pronated foot type as a significant risk factor for MTSS. Likewise, application of precise methods to quantify the structural characteristic of lower extremity in this study, made us possible to better define the alignment that may or may not contribute to injury.

It is important to prospectively identify modifiable risk factors so that strategies may be adapted to minimize injury occurrence. If risk for injury can be identified prior to the training season using navicular drop test normalized to foot length, interventions such as custom orthotics or shoe wear prescription may be recommended to the runner to help minimize potential injuries and time lost from sport participation [31]. Prevention methods that should be considered are, shock-absorbent insoles, foam heel pads, Achilles tendon stretching, footwear, and graduated running programs [31, 32].

A significant relationship was found between navicular drop and MTSS in this study. But we did not find any relationship between lower extremity alignment and MTSS. MTSS had no significant correlation with other variables including Q, Tibia and Achilles angles, intercondylar and intermaleolar lengths and lower extremity lengths.