The medial tibial stress syndrome (MTSS), first described by Mubarak et al. in 1982 [1
], is one of the most common painful exercise-induced leg injuries [2
]. MTSS encompasses several injuries, including medial tibial periostitis, soleus enthesopathy, and shin splints [3
]. However, the aetiology of this condition has been debated for years, and MTSS continues to be an intriguing and confusing pathological condition. Pain associated with MTSS commonly occurs in the middle or distal third of the posteromedial border of the tibia [3
]. The site of pain is typically spread over a minimum of 5 cm [6
]. In contrast, a stress fracture has an area of focal tenderness of only 2–3 cm [7
]. Advanced MTSS patients commonly experience pain at the onset of activity [9
]. Military studies have indicated that the incidence of MTSS is 6–38 % [5
]. The recovery time for the resolution of MTSS ranges from 4 weeks to 18 months [9
], and MTSS is often refractory to conservative management. MTSS is proposed to be triggered by internal (tibial alignment, flat foot, low medial longitudinal arch, and forefoot varus) and external factors (over work, sports surface, shoes) [5
], although these causes remain largely speculative. A previous study suggested the use of an evidence-based prevention method [13
], but effective methods for treatment and prevention have not been established and further studies of MTSS are urgently required. An assessment of the static and dynamic alignment of the rearfoot in MTSS is necessary to understand the kinematics related to MTSS.
Static malalignment of the lower extremity has been shown to increase the risk of developing MTSS in athletes [12
]. In addition, many studies have reported the kinematic characteristics of MTSS, such as rearfoot eversion [15
], increased free moment [17
] and loading rates [18
], tibial shock [19
], and hip external rotation [14
]. However these studies performed motion analysis with skin markers. Skin markers mounted upon externally identifiable bony landmarks of the foot do not follow the underlying individual skeletal segments during movement [21
]. Motion analysis using skin markers does not allow the investigation of the subtalar joint (especially talus) movement [22
]. Intracortical pins have also been used to more accurately measure in vivo rearfoot motion kinematics [23
], but this method is invasive and the restricted motion of bone pin markers makes these internal markers difficult to implement. In contrast, 3-dimensional to 2-dimensional (3D-2D) model registration techniques have been used for the analysis of rearfoot motion without the use of invasive markers [25
]. However, no prior study has used 3D-2D model registration to assess static and dynamic rearfoot behaviour in MTSS. The 3D-2D model allows to study the characteristics of patients with MTSS in terms of malalignment and kinematics, contributing to an improved understanding of MTSS.
Therefore, the aim of the present study was to investigate MTSS using 3D-2D model registration to obtain accurate structures of the rearfoot during the forward step. Hypothesis was set that MTSS patients would have greater subtalar joint pronation (dorsi flexion, eversion, external rotation), compared to healthy individuals, during the forward step.
The purpose of this study was to reveal the characteristics of the static alignment and rearfoot motion during a forward step in MTSS patients. The subtalar joint of patients with MTSS was characterized by an increased range of motion in internal/external rotation and inversion/eversion during the forward step. In addition, the calcaneal pitch was lower and the navicular height change was greater in MTSS patients.
Pronation in MTSS patients
In this study, MTSS patients showed more external rotation and eversion of the subtalar joint than that observed in normal participants. Moreover, the kinematics of the subtalar joint had a tendency in almost every case.
Campbell et al. reported an eversion peak of 8.7° for the normative rearfoot (calcaneus relative to tibia) during walking with biplane cineradiography [32
]. With regard to the difference in the magnitude of eversion in this study compared to the Campbell study, this may have occurred because the rearfoot movement in this study included the subtalar joint and the talocrural joint.
The previous study is research related to the motion of dynamic foot in MTSS patients. Pohl et al., using logistic regression analysis, indicated that in female runners with tibial stress fractures, peak rearfoot eversion during a forward step was an important variable [15
]. Standing foot pronation and longitudinal arch were greater in MTSS patients than in healthy participants [12
]. However, these previous studies employed uniplanar measurements. It is significant that our study used the 3D-2D model registration technique to evaluate the 3-dimensional kinematic characteristics of MTSS patients during a forward step.
Recently, several studies have investigated the relationship between MTSS and the kinematics of the lower extremity. The occurrence of tibial stress fractures in female runners was related to greater vertical loading rates of the lower extremity [17
]. Athletes with shin splints had increased rear foot inversion and eversion during passive mobility [16
]. Additionally, peak rearfoot eversion in athletes with MTSS [16
] and peak rearfoot eversion of athletes with tibial stress fractures were significantly higher than those of normal participants [34
]. Thus, the lower extremity that is affected by MTSS is believed to be associated with abnormal foot motion.
However, the pathophysiology of MTSS has been a subject of controversy.
The potential development of methods for preventing MTSS requires further study to investigate how subtalar pronation affects MTSS injury.
Increased navicular height change in MTSS patients (Static alignment)
In this study, we found that static navicular height change was greater in MTSS patients compared to healthy participants. Several studies have examined the relationship between navicular drop and MTSS [10
]. The use of navicular drop to assess foot pronation has been especially useful in MTSS patients [24
]. Additionally, a point-biserial correlation of 0.42 between the navicular drop test and the occurrence of MTSS was discovered, indicating a positive relationship between navicular drop, a measure of pronation, and MTSS injury [10
]. In these studies, the navicular drop was greater in MTSS patients than in healthy participants [10
]. In contrast, Hubbard et al. reported that there was no relationship between MTSS and navicular drop [37
]. These conflicting results are possibly caused by methodological differences. Almost all studies evaluated navicular drop using skin markers, and the reliability of this method has been reported as difficult to evaluate [34
]. The present study used radiography, which is a more precise method, and we found that navicular height change was greater in MTSS patients.
Calcaneal pitch in MTSS patients (Static alignment)
In the present study, the calcaneal pitch was lower in MTSS patients compared to healthy participants (14. 3° vs. 20.75°, p
= 0.017), indicating that a low calcaneal pitch may be associated with MTSS. Other researchers found that the calcaneal pitch of normal participants was 20°–22.5° during standing [31
]. The calcaneal pitch angle is to patients with pes planus [30
], and the presence of flat-feet types are used to patients with lower extremity injuries [39
There are several limitations to the current study. First, considering the anatomy and functions of the rearfoot, more specific and precise studies concerning the subtalar joint are needed to validate the accuracy of the analysis. Second, our analysis range included only one forward step starting from a static standing position. Sports activities have a number of movements (e.g., running, cutting, stopping and turning, etc.), and therefore, further investigation of these motions in MTSS patients is needed. Third, the measurement of activity was limited to a single event to minimize radiation exposure. Importantly, the participants practiced the activity before the recorded event to ensure reproducibility and reduce inter-subject variability. Finally, the precision of the bone model in this study was not validated. Because this study performed matching from the sagittal plane of the cineradiograph, studies using biplane cineradiography with greater detail are necessary in the future. Further investigations will help more clearly elucidate these topics.
The authors state that they have no financial competing interest and source of funding.
KA, TF conceived and designed the study, KA, BN, MF, SM, TF performed the experiments, KA, MF, NH performed data analysis and drafted the manuscript. MF, NH contributed to discussion and reviewed/edited the manuscript. All authors edited and approved the manuscript prior to the submission.