It is not the first time that we have talked about fractures: we have already done so in this clinical case to support diagnosis and in this other one on complex fractures. In today's article, we will talk about stress fractures, a frequent, severe injury common in high-performance sports (Sobhani et al. 2013). It occurs most frequently in long bones that receive a lot of impact from the lower limb, such as the metatarsals, calcaneus, or tibia (Finestone et al. 2011), but it can happen in any bone, as in the case of rowers, who have rib stress fractures (Kiel et al. 2022). It is not surprising that it is an injury of special relevance in the military environment (May et al. 2022; Hughes et al. 2022) where long-duration training is done with small recovery times; in skate-boarding (Andrew-Naylor et al. 2021), sport with multiple jumps on hard ground; and of course, in soccer (Okunuki et al. 2022; Matsuda et al. 2017).
Stress fractures in high-performance athletes occur due to the accumulation of low-intensity and repeated shocks to which the bone is not used to. For this reason, there are numerous studies that relate a particularly hard playing field or with little impact absorption with the incidence of stress fractures in the lower limb (Winson et al. 2020; Miyamori et al. 2019; Thomson et al. 2018).
However, it is not the change of playing field that explains this injury, but rather the poor control of loads and the non-gradual increase in their intensity. A high training load for someone who is used to it and has gradually increased it in the past is unlikely to be affected by this type of injury. On the contrary, training of greater intensity or duration than usual, for an unconditioned athlete, will pose a significant risk of suffering a stress fracture, since their osteoblasts will not respond to the demand for bone repair (Warden et al. 2014).
In fact, multiple high-intensity, high-impact training loads, leading to great muscle fatigue, or simply a prolonged period of tiredness, will reduce the effectiveness of the muscles in controlling the movement of the body during contact with the ground. Therefore, shock absorption will be much less effective and forces will be transmitted to the bone (O'Leary et al. 2021), as exemplified by the change of direction in Figure 1.
Figure 1. Example of a change of direction made by a soccer player. It is a common and non-traumatic action, which can, however, become a traumatic action in the case of a player with a weakened bone and less reactive to shock absorption.
The last of the most important factors is dietary deficiency. A deficiency of minerals, especially calcium and magnesium, as well as vitamin D, can predispose to low-density bone, which is more susceptible to fracture. In prevention, nutritional strategies, especially with the contribution of Vitamin D and calcium, seem to significantly reduce the appearance of stress fractures in high-performance athletes (Knechtle et al. 2021).
In general, the pain is precise and very well localized (Patel et al. 2011). At first, the pain may disappear between training sessions, but it will gradually increase in intensity and duration, although it is not predictive of this injury (Milgrom et al. 2021). For this reason, and because of the long recovery time, prevention is such an important key.
Baropodometry, within the means of evaluating this pathology, has shown that there is a very interesting relationship between the risk of stress fracture injury and asymmetry in plantar pressure (Azevedo et al. 2017), as can be seen in Figure 2, extracted from Wafai et al. 2015:
Figure 2. 2D and 3D representation of a plantar pressure distribution within the shoe resulting from metatarsalgia in the pathological foot. Extracted from Wafai et al. 2015.
Upon diagnosis, stress fractures often go unnoticed on usual X-ray. Most of the time, a bone scan (scintigraphy) will be recommended when this lesion is suspected (Castropil et al. 2018) or an image by magnetic resonance imaging (Expert Panel on Musculoskeletal Imaging, 2017). Figure 3 (Nussbaum et al. 2022) shows the usual resonance finding in these lesions.
Figure 3. Magnetic resonance imaging findings of a patient with a grade 4 stress fracture of the proximal tibia. Arrows show edema and a horizontal fracture line on fat-suppressed T2 and T1 images. Extracted from Nussbaum et al. 2022.
These are expensive tests and, even at low and medium radiation levels, respectively, they are not harmless. For this reason, thermography is postulated as a low-cost and non-invasive test that contributes to the diagnosis of this pathology.
The scientific literature regarding thermal findings in patients with stress fractures is not particularly extensive, however, there are some clinical case articles of relative importance.
Almost 40 years ago, we found two very illustrative articles on this pathology. In the first of them (Devereaux et al. 1984), 18 patients with suspected stress fracture in the tibia or fibula were included. 15 of them are positively diagnosed by means of a scintigraphy. In addition, it is shown that the use of thermography is superior to other tests, such as the ultrasound pain induction test or X-ray. Finally, data on the sensitivity of thermography is provided, this being 80%, as shown in figure 4:
Figure 4. Compilation of the 15 cases with abnormal scintigraphy, collecting data on the injured region, the duration of the pain and the positive or negative result of the pain induction test by ultrasound, thermogram and plain radiography. Extracted from Devereaux et al. 1984.
A year later, another similar study appeared (Goodman et al. 1985) in which 17 patients with symptoms compatible with stress fracture were analyzed with thermography, X-ray and nuclide contrast scintigraphy. Only 9 were finally diagnosed with stress fractures. Thermographic analysis revealed data on sensitivity (82%), specificity (83%), negative predictive value (71%) and positive predictive value (90%).
Finally, we found an article (Arthur et al. 2011) that has a sample of 147 Australian Army soldiers, who regularly performed impact training, having 20% stress fracture injuries. What is interesting about this study is that the symptomatic cases were detected by thermography and confirmed by an imaging test (scintigraphy). All negative cases continued their training routines normally; however, positive cases were sent home until recovered for later reinstatement to the Navy.
Today's clinical case is a professional soccer player who had a stress fracture. Figure 1 exemplifies the type of action performed by the player at the time of the fracture. Two months later, he was signed by another team from the first division of LaLiga (Spain), where he underwent a thermography analysis. The results can be seen in figure 5, where hyperthermia in his right foot is evident, typical thermal behavior in a case of bone fracture. In addition, we have magnetic resonance images confirming a break in continuity in the tail of the fifth metatarsal of the right foot.
Figure 5. First thermographic image of subjects, showing evident hyperthermia in the injured region and their magnetic resonance of the fracture in the fifth metatarsal.
The interesting thing about this clinical case is that we have a follow-up, shown in figure 6. We can observe a reduction in his thermal asymmetry in the subsequent sessions, which verifies the efficacy of the treatment and the positive evolution in recovery. This becomes evident by viewing the graph of the reduction in mean asymmetry in the foot region. But we can also observe it in the thermograms and, above all, in the avatars, which clearly show a reduction in the quantity and severity of the asymmetries of the ankle-foot regions and those of the sole of the foot.
Figure 6. Thermographic follow-up of a professional soccer player in the months after a stress fracture until his complete recovery (RTP).
Thermography is a powerful evaluation and follow-up tool in cases of stress fracture in high-performance athletes, an injury with a relatively high incidence, but above all of high severity, which implies a prognosis of several weeks or even months. Compared with other tests, the results in the basic statistical indicators (sensitivity, specificity, positive predictive value and negative predictive value) are superior in thermographic analysis, but inferior to gold standard tests such as scintigraphy or magnetic resonance imaging. The most common thermal behavior in cases of stress fracture is asymmetric-hyperthermic and, after the recovery period and following an adequate treatment, the thermal evolution should tend towards the reduction and even the suppression of the asymmetry. Thanks to this monitoring, recovery plans can be established based on the degree of thermal asymmetry found.
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ThermoHuman has had the support of the Funds of the European Union and the Community of Madrid through the Operational Programme on Youth Employment. Likewise, ThermoHuman within the framework of the Export Initiation Program of ICEX NEXT, had the support of ICEX and the co-financing of the European Regional Development Fund (ERDF).
Thermohuman has received funding from the Centre for the Development of Industrial Technology (CDTI), in participation with the European Regional Development Fund (ERDF), for the R+D activities involved in creating a new tool, based on thermography, for the prediction and prevention of rheumatoid arthritis. See project detail.
