Arches of the Foot
The foot is the region of the body distal to the leg and consists of 28 bones. These bones are arranged into longitudinal and transverse arches with the support of various muscles and ligaments. There are three arches in the foot, which are referred to as:
- the medial longitudinal arch
- the lateral longitudinal arch
- the transverse arch
These arches have an important role in standing, walking and running. This article will discuss the anatomical structure and function of these arches, followed by any relevant clinical pathology.
Medial Longitudinal Arch
The medial longitudinal arch is higher than its lateral counterpart and is visible between the heel of the foot proximally and the medial three metatarsophalangeal joints distally.
The bones participating in the formation of the arch are the following:
- the medial three metatarsals up to their heads
- the sesamoid bones
- the three cuneiforms
- the navicular
The arch consists of two pillars. The anterior pillar consists of the medial three metatarsal heads whilst the tuberosity of the calcaneus forms the posterior pillar.
The supporting ligaments provide more stability than the bones of the arch. One of these ligamentous structures, the plantar aponeurosis, acts as a supporting beam between the two pillars. Another important structure, the spring ligament, supports the head of the talus. The talocalcaneal ligament and the anterior fibres of the deltoid ligament also provide stability for this arch.
Muscles in the foot also help support the medial longitudinal arch. These include:
- flexor hallucis longus
- flexor digitorum longus
- abductor hallucis
- flexor digitorum brevis muscles
- tibialis posterior, which is the most important muscle in the maintenance of the arch as damage to its tendon results in collapse of the arch.
The tibialis posterior and anterior muscles help to raise the medial border of the arch whilst the flexor hallucis longus acts as a bowstring.
Lateral Longitudinal Arch
The less prominent lateral longitudinal arch is formed by the following:
Like its medial counterpart, the lateral arch consists of two pillars, which help support the arch. The anterior pillar consists of the fourth and fifth metatarsal heads whilst the calcaneus forms the posterior pillar. The main contributor to stabilisation of the arch is the fibularis longus tendon.
Ligaments also have an important role in the stabilisation of this arch and include the plantar aponeurosis and the long and short plantar ligaments, which act as bowstrings beneath the arch. Other muscles and tendons, apart from the fibularis longus tendon, which contribute to the maintenance of this arch, include:
- lateral two tendons of flexor digitorum longus assisted by flexor accessorius
- abductor digiti minimi
- lateral half of flexor digitorum brevis
- fibularis brevis
- fibularis tertius
The transverse arch runs in a coronal plane and consists of the following:
- the five metatarsal bases
- the cuboid
- the cuneiform bones
The intermediate and lateral cuneiforms are wedge shaped which aids in maintenance of the arch. The medial and lateral longitudinal arches act as pillars for the transverse arch.
The important ligaments of this arch are the ligaments between the cuneiforms and bases of the five metatarsal bones.
The curvature of the arch is mainly maintained by the fibularis longus tendon, assisted by the tibialis posterior tendon, which both cross under the sole of the foot. The deep transverse ligaments, the transverse head of adductor longus and the fibularis longus tendon, also help to stabilise this arch.
Function of the Arches
The arches of the foot have an important role in weight bearing. During standing, the weight of the body is distributed throughout the bones in the foot by the arches. The weight is transmitted from the tibia to the talus, before being transmitted posteriorly to the calcaneus. It is also transmitted anteriorly to the navicular, cuneiforms and metatarsals. The lateral longitudinal arch is mostly involved in transmitting this weight and makes more contact with the ground than the medial one.
The medial longitudinal arch also has an important role in shock absorption and propulsion during walking, running and jumping. The arch acts like a springboard, as its anterior pillar is the point of take-off during these activities. The process of walking is referred to as the gait cycle and this consists of two phases: a stance phase and a swing phase. During the stance phase, the forefoot pronates which flattens the medial longitudinal arch and the transverse arch. During the swing phase, the hind foot supinates which causes the medial longitudinal arch to elevate. This high arch acts as a rigid lever for propulsion.
Pes planus, an excessively flat foot, may be physiological or pathological. When it is pathological, it can cause stiffness and pain of the foot. The Windlass Test can determine if pes planus is pathological and involves passive dorsiflexion of the hallux at the metatarsophalangeal joint. In pathological pes planus, there is no accentuation of the medial longitudinal arch as a result of this movement. Causes of this condition include arthritis of the tarsometatarsal, talocalcaneal and subtalar joints as well as damage to the tibialis posterior tendon or to the spring ligament. It can also be caused by tarsal coalition, which is when an abnormal connection forms between two of the tarsal bones.
On the other hand, an excessively arched foot is referred to as pes cavus, or claw foot. This usually occurs as a result of a neurological disorder such as Charcot-Marie-Tooth disease and poliomyelitis. In Charcot-Marie-Tooth disease, the fibularis longus muscle is overactive, resulting in plantar hyperflexion of the first metatarsal. This results in hindfoot varus, where the calcaneus is adducted and rotated under the talus bone. In order to test for this condition, a Coleman Block Test is a carried out, which is where the patient stands on a wooden block with the lateral part of their forefoot. If the hindfoot varus is flexible, the deformity will correct itself spontaneously. Surgery may be indicated if the hindfoot is rigid.