## 4 Discussion  
Employment of rasterstereographic-system Formetric-4D postural evaluation technique represents a valuable tool for studying and for imaging acquisition of the entire spine. This device presents a good degree of validity in comparison to exams using X-rays [21]. Moreover, it presents an excellent intra/inter-operator reliability and a good validity for inter- and intraday measurements [18]. Validity of rasterstereography compared to X-rays assessments have been confirmed by [PERSON] et al. [22], identifying the first technique as a method which simplifies spine analysis without radiation use and which allows to detect different spine deformities like thoracic kyphosis or the most common scoliosis. Rasterstereography, indeed, appears to be related to Raimondi method for the evaluation of vertebral rotation in young patients with idiopathic scoliosis, with the advantage of being easily repeatable for screening and follow-up, without any risk of exposure to ionizing radiations [16]. Compared to traditional radiography, rasterstereography presents the disadvantage to be influenced by subcutaneous tissue thickness, which can consequently alter the evaluation of the parameters related to spine internal morphology [22]. In literature, different studies focused their attention on an eventual correlation between sport typology and postural adaptations. It has long been known that there are various factors which can influence paravertebral musculature, and among them an important role is attributed to the typology of sport activity performed [23]. For example, a symmetrical sport as soccer considerably affects liiopsoas muscle tone on both body sides, in comparison to tennis (asymmetrical sport) in which liiopsoas muscle hypertrophy occurs mainly on one side. This also applies to gluteal musculature, which shows unilateral hypertrophy in tennis players, while muscle tone appears to be balanced in soccer players and sedentary subjects [24]. Furthermore, sports activity can even significantly affect sagittal curvatures of the spine, increasing dorsal kyphosis [25; 26]. A study performed in 2017 at Cairo University analyses how sagittal curves in volleyball players, mainly males, are characterized by an increasing trend of the normal dorsal kyphosis. However, sport typology can also have an impact on the development of degenerative vertebral pathology, as occurs in throwing sports (discus throwers) and sports that involve high jump. During these activities, the spine is subjected to a stress, such as to result in degenerative alterations, especially in those sport typologies involving a repeated flexion-extension movement of the spine [27]. Through the use of rasterstereography it has been noticed how an asymmetrical sport, like tennis, could influence different parameters of posture, like rotation of vertebral surface, trunk length (distance between prominent vertebra and the median point between the two lumbar dimples) and lateral right or left deviations, depending on training sessions number, but also on the level of sport experience of each athlete [24]. Moreover, through the implementation of rasterstereography, it has been demonstrated how sport (symmetrical and asymmetrical) could influence posture of children aged between 8 and 12 years. It has been observed how weekly training hours increase reduces thoracic kyphosis on sagittal plan and lateral deviation on frontal plan with a consequent improvement of erect posture [28]. Another study performed in 2015 at Napoli University focused on investigating the incidence of eventual postural anomalies in 14 water-polo female players. Nevertheless, this study did not demonstrate any correlation between the typology of performed sport and postural adaptations, even if authors support the idea that eventual postural adaptations could affect spine development during growth. Regarding the comparison between sedentary subjects and asymmetrical sport players, statistically valid postural variations on transverse plan have been observed.