# Study of Force Changes Based on Orthotic Elements Under the First Ray
## 1 Introduction  
The first ray plays a crucial role in the biomechanics of gait, particularly during mid-stance and propulsion in the support phase. It contributes to the formation of the medial longitudinal arch of the foot, adapting to terrain irregularities and acting as a rigid segment that propels the body weight forward [1]. The dorsiflexed first ray, initially described by [PERSON] [2] in 1938 as metatarsus primus elevatus, is characterized by a position in which the head of the first metatarsal lies above the plane of the other metatarsal heads. Today, the definition of metatarsus primus elevatus places greater emphasis on movement, affecting the normal function of the footand leading to a variety of symptoms [3]. A first ray is considered to exhibit this morpho-functional alteration when it shows a range of dorsiflexion greater than plantarflexion from its neutral position. From a biomechanical perspective, the first ray plays an essential role in the propulsion process of the foot during gait, assisting in the transfer of weight to the hallux and stabilizing the foot during push-off. The dorsiflexion of the first ray appears to disrupt this process by preventing the first metatarsal from aligning properly with the rest of the metatarsals during stance, resulting in uneven force distribution and potentially inducing pain in the area of the first metatarsal head, as well as in other parts of the foot, such as the second metatarsal. This condition can lead to dysfunction in the function of the medial longitudinal arch and altered force distribution during the gait cycle, especially during the mid-stance and propulsion phases [2; 4]. The clinical consequences include pain in the first metatarsal area, difficulty with propulsion, and possible problems in other structures of the foot, such as the hallux valgus or metatarsalgia [5; 6; 7; 8; 9]. [PERSON] [5], building on [PERSON]'s [6] classification for the plantarflexed first ray, developed a new categorization for the metatarsus primus elevatus. This classification distinguishes three types: flexible, when the first ray can plantarflex and lie below the other metatarsal heads; semi-flexible, when it reaches the level of the other metatarsal heads; and rigid, when its plantar flexion capacity is insufficient to align with the other metatarsals. This alteration can have either a congenital or acquired origin [10]. Several studies have evaluated the validity and reliability of the techniques and methods used to measure the mobility of the first ray [11; 12; 13; 14]. The treatment of the first metatarsophalangeal segment focuses on reducing symptoms without restricting the plantar flexion of the first ray [15], with pediatric interventions being the primary option. Foot orthoses aim to improve foot functionality, with specific adaptations based on the classification of the deformity. The pathological pronation of the hindfoot is one of the main factors contributing to the misalignment and progression of various pathologies of the first ray, such as hallux valgus. This biomechanical alteration causes an abnormal distribution of forces during gait, which generates additional stress on the metatarsophalangeal joint and promotes a progressive deformity. Orthotic insoles play a crucial role in the management of these pathologies because, by correcting excessive pronation, they allow for a more equitable distribution of loads and improve the foot alignment, which, in turn, optimizes gait and delays the progression of the deformity [5]. Despite the clinical use of orthoses for first-ray pathologies, the evidence quantifying their biomechanical impact on three-dimensional force vectors remains limited. Previous studies [16; 17; 18] have primarily focused on mobility assessments or plantar pressure outcomes, with scarce data derived from dynamometric platforms analyzing the mediolateral (X), antero-posterior (Y), and vertical (Z) forces.