Biomechanical assessment in HAV treatment

Hallux Abductus Valgus (HAV) is a pathology that affects the fi rst metatarsophalangeal joint, in which there is a medial displacement of the metatarsal and a lateral deviation of the hallux, causing joint dysfunction and disability in the patient. There are two types of treatments for this condition (conservative and surgical), and both require an exhaustive biomechanical assessment, since biomechanics are the main cause of this deformity. The main objective of the article is the development of a biomechanical examination and assessment algorithm to be carried out systematically in patients with HAV. Research Article Biomechanical assessment in HAV treatment Ma Ángeles Rodríguez Personat*, Fernando Chacón Giráldez, Lidia Carvajal Moreno and Ana Juana Pérez Belloso Department of Podiatry, Faculty of Nursing, Physiotherapy and Podiatry, University of Sevilla, 41009 Sevilla, Spain Received: 11 May, 2021 Accepted: 31 May, 2021 Published: 02 June, 2021 *Corresponding author: Ma Ángeles Rodríguez Personat, Department of Podiatry, Faculty of Nursing, Physiotherapy and Podiatry, University of Sevilla, 41009 Sevilla, Spain, E-mail:


Introduction
Hallux Abductus Valgus (HAV) is a deformity that affects the forefoot in which there is a medial deviation of the fi rst metatarsal and the lateral deviation of the fi rst toe.
Currently this condition affects around the 26% of the adults worldwide, being 36% of those affected over 65 years. In addition, HAV has a higher prevalence in the western countries and a lower prevalence in the eastern, where it began to increase in the mid-20th century with the use of high-heeled and narrow toe-box shoes [1,2].
The etiology of HAV is biomechanical, therefore, to solve the problem we must know the cause, and so we have to carry out a good biomechanical exploration.

Static evaluation
Hip evaluation: Using the Trendelenburg test, which consists of observing the patient in a single limb-stance position on the affected limb for 30 seconds. The examiner places his hands or a levelometer on the iliac crests to observe their alignment. It is considered positive if, in the position of single leg stance, the hip falls to the opposite side. A positive sign of this test would indicate weakness of the gluteus medius and minus (hip abductors) [1].
Knee evaluation: Measured with a two-branch goniometer the knee that we are exploring and the dynamic observation of these. Observed the presence of genu varus or genu valgus, this indicates joint incongruity caused by pathological pronation.
Also, we must assess if the knee fl exion / extension is complete or if there is pain when moving it [2].
Ankle evaluation: Equinus deformity is the main cause of pathologies related to the gait cycle, directly linked to the ankle joint. this joint we have the Achilles tendon, one of the reasons of the equinus [3]. As a direct consequence of this equinus condition, we can also appreciate Hallux Valgus, and many other alterations in the forefoot such as hammer toes, metatarsal pain, narrow heel sign, genu recurvatum or hyperlordosis [4].
In this examination: the Silfverskjöld Test is performed. It is used to identify equinus deformity when the ankle and the knee are in extension. This situation is not perceived when the knee is fl exed. Despite the clinical examination of the test, we can refer to additional clinical signs that may give us evidence of shortening of gastrocnemius [5], wherever, the Silfverskjöld Test doesn´t allow identify shortening of soleus.
To evaluate the soleus muscle: we must perform ankle dorsifl exion while keeping the knee fl exed [5]. Subtalar joint evaluation: To achieve a correct function of this joint, it is required at least 8º of range of motion [6].
In this case, we assessed the clinical axis of the calcaneus. It was evaluated in a standing position and quantifi ed the axis that was formed between the distal third of the tibia and the posterior surface of the calcaneus. The reference values are between 0º and 5º.
Achilles-calcaneus-plantar system evaluation: Anatomically, there is a relationship between the posterior leg muscles (gastrocnemius) and the HAV through the fascia. This is due to the anatomical situation of the gastrocnemius (insertion in the calcaneus), the medial band of the plantar fascia (origin in the calcaneus and insertion in the 1st metatarsophalangeal joint).
To checked the correct functioning of the achillescalcaneus-plantar system, the patient is asked to stand on tiptoe and, if this is correct, the calcaneus inverts [7].

First ray evaluation:
This joint presents mobility in the 3 planes of space, so when performing dorsifl exion it is accompanied by an inversion (dorsifl exion + inversion) and when performing plantarfl exion by an eversion (plantarfl exion + eversion). When the 1st ray has no more dorsifl exion or inversion capacity, the subtalar joint continues pronating and the foot fully everts. The reference values are around 5 mm of dorsifl exion and 5 mm of plantarfl exion [8][9][10][11].
To assess the fi rs ray, the subtalar joint was placed in a neutral position and the minor metatarsals are hugged with one hand and the 1st metatarsal is mobilized in dorsal fl exion and plantar fl exion. With the help of a goniometer, we assessed the greater range of motion and this will indicate the position of the metatarsal [8,12].
To rate the stability of the 1st metatarsal we assessed the peroneus longus muscle [13]. For this, we asked the patient to lie supine or in a sitting position, we placed the homolateral hand to the foot that we are going to explore holding the retromalleolar area, the other hand is placed in the plantar and external surface of the foot for making resistance and we ask the patient to do eversion along with plantar fl exion of the ankle.

1st Metatarsophalangeal joint evaluation
For the measurement we marked two reference points. Point one, which corresponds to the midline of the medial phalanx, and point two which corresponds to the midline of the fi rst metatarsal, both on the tibial surface of the foot. We placed the mobile and fi xed branches of a goniometer respectively and did the movement of fl exion and extension of the joint, so that we obtained the degrees of movement. This is done both in a standing and unloading position [8,11,14].
We need 60º of extension of this joint in order to a correct gait. When measuring metatarsophalangeal joint extension with the ankle in a 90º position to the leg, 10º less is obtained than measuring it with the ankle in a relaxed position [8]. This is determined by the relationships between the muscles of the leg, specifi cally the gastrocnemius, and the metatarsophalangeal joint [15].
In the period of support: The pelvis generates maximum internal rotation and swings towards the limb that is oscillating.
The abductor muscles contract to stop the pelvic swinging.
In the propulsive phase: The pelvis is in external rotation, however, in the frontal plane there is no swinging towards the contralateral limb and in the sagittal plane there is anteversion.
Regarding the musculature, the hip adductors contract for the fi rst time, together with the iliac psoas, whose function is to stop the hip hyperextension that is generated by moving the trunk forward. In patients with HAV, the hip has an abnormal balance, abduction is decreased and adduction is increased, and the pelvis of the limb in which the HAV is located has a lower height [17]. Furthermore, all these abnormalities are directly related to subtalar joint pronation, thus establishing a direct relationship between HAV and pelvis, as is the case with the knee joint. [18].
Knee evaluation: Patients with HAV have a decreased maximum extension in the oscillating phase [17].

Ankle evaluation:
The center of the ankle joint determines the tendency to internal or external tibial torsion, depending on whether it is medialized or lateralized [2,14] .
In the period of heel contact: The ankle is in a slight dorsal fl exion, and from this moment it begins progressively to perform plantarfl exion. The muscles involved in this period are tibialis anterior (slowing plantarfl exion of the ankle) and tibialis posterior (control of subtalar joint pronation) [2]. In this period, we must observe if the ankle dorsifl exion is enough and if the pronation of the subtalar joint is completely controlled by the musculature. In patients with HAV, the ankle dorsifl exion movement is decreased [17,19]. This situation is caused by a shortening of the gastrocnemius (mainly the medial one), which are anatomically related to the metatarsophalangeal joint throughout the achilles-calcaneus-plantar system [5,20].  where the weight falls on the head of the 1st metatarsal and the foot takes off as a rigid and propulsive lever [2,16].
In patients with HAV, there is an excessive pronation of the subtalar joint or an abnormality of this during any stage of the gait cycle, mainly in the propulsive period. As a result, it produces an abnormal function of the peroneus longus muscle and an instability of the fi rst ray during the propulsion [22][23][24][25][26].