Foot and Ankle Structure and Function
- 1 Anatomy
- 2 Kinematics
- 3 Arthrokinematics
- 4 Influence on Kinetic Chain
- 5 Arches of Foot
- 6 Function of the Foot
- 7 References
The foot and ankle form a complex system which consists of 28 bones, 33 joints, 112 ligaments, controlled by 13 extrinsic and 21 intrinsic muscles. The foot is subdivided into the rearfoot, midfoot, and forefoot. It functions as a rigid structure for weight bearing and it can also function as a flexible structure to conform to uneven terrain. The foot and ankle provide various important functions which includes: supporting body weight, providing balance, shock absorption, transferring ground reaction forces, compensating for proximal malalignment, and substituting hand function in individuals with upper extremity amputation/paralysis.
The talocrural joint is formed between the distal tibia-fibula and and talus, and is commonly known as the ankle joint. The distal and inferior aspect of the tibia – known as the plafond – is connected to the fibula via tibiofibular ligaments forming a strong mortise which articulates with the talar dome distally. It is a hinge joint and allows for dorsiflexion and plantarflexion movements in the sagittal plane.
Subtalar (ST) Joint
It is also known as the talocalcaneal joint and is formed between the talus and calcaneus. The talus has three facets (anterior, middle and posterior) which articulate inferiorly with the calcaneus.
Midtarsal (MT) Joint
Also known as transverse tarsal joints or Chopart’s joint. It is an S-shaped joint when viewed from above and consists of two joints – the talonavicular joint and calcaneocuboid joint.
- Talonavicular (TN) Joint - Formed between the anterior talar head and the concavity on the navicular. It does not have its own capsule, but rather shares one with the two anterior talocalcaneal articulations.
Tarsometatarsal (TMT) Joint Complex
Also known as Lisfranc’s joint. The distal tarsal rows including the three cuneiform bones and cuboid articulate with the base of each metatarsal to form the TMT complex. It is an S-shaped joint and is divided into 3 distinct columns:
- Medial – composed of 1st metatarsal and medial cuneiform
- Middle – composed of 2nd and 3rd metatarsals and intermediate and lateral cuneiforms, respectively
- Lateral – composed of 4th and 5th metatarsals and the cuboid; it also divides the midfoot from forefoot
Metatarsophalangeal (MTP) Joints and Interphalangeal (IP) Joints
The MTP joints are formed between the metatarsal heads and the corresponding bases of the proximal phalanx. The interphalangeal joints of the toes are formed between the phalanges of the toes. Each toe has proximal and distal IP joints except for the great toe which only has one IP joint.
|Joint||Type of Joint||Plane of Movement||Motion|
|TC joint||Hinge||Sagittal||Dorsiflesxion & Plantarflexion|
Inversion & Eversion
Dorsiflexion & Plantarflexion
TN joint - Ball and socket
CC joint - modified saddle
Largely in transverse
Inversion & Eversion
Flexion & Extension
Flexion & Extension
Abduction & Adduction
|IP joint||Hinge||Sagittal||Flexion & Extension|
The tip of the medial malleoli is anterior and superior to lateral malleoli, which makes its axis oblique to both the sagittal and frontal planes. The axis of rotation is approximately 13-18o laterally from frontal plane and at angle of 8-10o from the transverse plane. Motion in other planes is required (like horizontal and frontal plane) to achieve a complete motion for plantarflexion and dorsiflexion. The normal available range for dorsiflexion is 0-30o and plantarflexion range is 0-55o.
The axis of the subtalar joint lies about 42o superiorly to the sagittal plane and about 16 to 23o medial to the transverse plane. The literature presents vast ranges of subtalar motion ranging from 5 to 65o. The average ROM for pronation is 5o and 20o for supination. Inversion and eversion ROM has been identified as 30o and 18o, respectively. Total inversion-eversion motion is about 2:1 or 3:2 ratio of inversion-to-eversion movement.
The midtarsal joint rotates at two axes due to its anatomy, making its motion complex. Longitudinal axis (image 'A' below) lies about 15o superior to the horizontal plane and about 10o medial to longitudinal plane. The oblique axis (image 'B' below) lies about 52o superior to the horizontal plane and 57o from midline. The longitudinal axis is close to the subtalar joint axis and the oblique axis is similar to the talocrural joint axis.
MT Joint Locking – An important function of the foot is propulsion of weight during stance phase. This function is made possible by MT joint locking and unlocking. During heel strike, the foot needs to be flexible in order to adjust to the surface and the MT joint unlocks to provide this flexibility. Later in the gait cycle, the foot then needs to act as a rigid lever to propel the weight of the body forward which is made possible by MT joint locking. During pronation/eversion of the foot, the axis of the TN and CC joints are parallel to each other, making it easier for them to independently move and unlock the MT joint. The axes cross each other during supination/inversion which locks the MT joint making it difficult to move. Blackwood et al concluded in the study that there is increased forefoot movement when calcaneus is everted. This is consisted with the MT joint locking mechanism.
Lisfranc Joint Complex
The degree of sagittal motion for each TMT joint is presented below:
|TMT Joint||Degree of Motion|
MTP and IP joints
The MTP joints are biaxial and move in sagittal and transverse planes. MTP joints have a greater sagittal plane movement and very little transverse plane movement. At the MTP joints, hyperextension is about 90o and flexion is about 30 to 50o. IP joints are hinge joints which limit motion in one direction.
- Talocrural Joint – Talus rolls within the mortise during dorsiflexion and plantarflexion. During dorsiflexion, the talus rolls anteriorly and it glides posteriorly. While with plantarflexion, talus rolls posteriorly and glides anteriorly.
- Subtalar Joint – Secondary to the anatomy of the subtalar joint, the coupled motion of dorsiflexion, abduction and eversion produces pronation, whereas the coupled motion of plantarflexion, adduction and inversion produces supination. It presents two point of articulations – anterior talocalcaneal articulation and posterior talocalcaneal articulation. During open kinectic chain inversion, the calcaneus rolls into inversion and it glides/slides laterally. And during eversion, the calcaneus rolls into eversion and it glides/slides medially
- Midtarsal Joint – For Talonavicular joint, the concave navicular moves on convex talus and hence the roll and glide is in the same direction of movement. The calcaneocuboid joint is a saddle joint so the direction changes depending on the movement. During flexion-extension, the cuboid is concave and the calcaneus is convex; hence, the roll and glide occurs in the same direction as the talonavicular joint. During abduction-adduction, however, the cuboid is convex and calcaneus is concave, and therefore the roll and glide occurs in the opposite direction.
- Lisfranc Joint – Secondary to bony and ligamentous anatomy of the complex, its primary role is stability of the midfoot and has very little movement. It has three distinct arches and the main stabilizing structure of TMT joint is a Y-shaped ligament known as Lisfranc’s ligament.
- MTP and IP Joints – Glide and roll is in the same direction as the movement for the MTP joints as the concave base of the phalanx moves on the convex head of the metatarsal. The same is true for the IP joints, where glide and roll is in the same direction as the concave distal phalanx moves on the convex proximal phalanx.
|Joint||Closed-Packed Position||Open-Packed Position||Capsular Pattern||Concave Surface||Convex Surface||
Roll & glide
|Talocrural joint||Full dorsiflexion||10o of plantarflexion and midway between pronation and supination||Limitation of plantarflexion, although clinically dorsiflexion limitation is more common||Proximal - Mortise formed by Tibia, tibiofibular ligament and fibula||Distal - Trochlear surface of Talar dome||Opposite direction|
|Subtalar joint||Full inversion||Inversion/plantarflexion||Limitation of inversion in chronic arthritis. Limitation of eversion in traumatic||Proximal - Anterior, middle and posterior facet of talus||Distal – Calcaneal Anterior, middle and posterior talar articular surface||Opposite direction|
|Talonavicular joint||Full supination||Midway between extreme ROM||Limitation of dorsiflexion, plantarflexion, adduction and internal rotation.||Proximal - Head of Talus||Distal - Concavity on Navicular bone for talus||Same direction|
|Calcaneocuboid joint||Full supination||Midway between extreme ROM||Limitation of dorsiflexion, plantarflexion, adduction and internal rotation.|| Distal - Cuboid is concave during flexion-extension.
Calcaneus is concave during adduction-abduction
| Proximal - Calcaneus is convex during flexion-extension.
Cuboid is convex during adduction-abduction
Flexion-extension = Same direction
|Lisfranc joint||Full supination||Midway between supination and pronation|
|1st MTP joint||Hyperextension||Slight (10o) extension||Loss of motion more in extension than flexion||Distal - Base of phalanx||Proxmial - Head of Metatarsal||Same direction|
|2nd to 5th MTP joint||Maximum flexion||Slight (10o) extension||Loss of flexion||Distal - Base of phalanges||Proximal - Head of metatarsals||Same direction|
|Interphalangeal Joint||Full extension||Slight flexion||Restriction in all direction with more in extension||Distal Phalanx||Proximal Phalanx||Same direction|
Influence on Kinetic Chain
As discussed above with MT joint locking, the transition of foot from pronation to supination is an important function that assists in adapting to uneven terrain and acting as a rigid lever during push off. During pronation, MT joint unlocks providing flexibility of the foot and assists in maintaining balance. And during supination, MT joint locks providing rigidity of the foot and maximizing stability. If the foot stuck pronated, this would lead to hypermobility of the midfoot and placing greater demand on the neuromuscular structure stabilize foot and maintaining upright stance. Whereas if the foot is stuck supinated, the midfoot would be hypomobile which would compensate the ability of the foot to adjust to the terrain and increasing demand on surrounding structure to maintain postural stability and balance. Cote et alconcluded that postural stability is affected by foot positioning under static and dynamic conditions. Chain reaction occurs secondary to positioning of the foot.
- Calcaneal eversion
- Adduction and plantarflexion of talus
- Medial rotation of talus
- Medial rotation of tibia and fibula
- Valgus at knee
- Medial rotation of femur
- Anterior tilting of pelvis
In closed chain movement following kinetic chain reaction with over-supinated foot takes place
- Calcaneal inversion
- Abduction and dorsiflexion of talus
- Lateral rotation of talus
- Lateral rotation of tibia and fibula
- Varus at knee
- Lateral rotation of femur
- Posterior tilting of pelvis
Arches of Foot
The arches of foot provide functions of force absorption, base of support and acts as a rigid lever during gait propulsion. The medial longitudinal arch, lateral longitudinal arch and transverse arch are the 3 arches that compromises arches of foot.
Medial Longitudinal Arch (MLA) – It is the longest and highest of all the arches. Bony components of MLA include calcaneus, talus, navicular, the three cuneiform bones and first 3 metatarsal. The arch consists of two pillar: anterior and posterior pillars. Anterior pillar consists of head of first 3 metatarsal heads whereas posterior pillar consists of tuberosity of calcaneus. Plantar aponeurosis forms the supporting beam connecting the two pillars. Apex of the MLA is superior articular surface of talus. In addition to plantar aponeurosis the MLA is also supported by spring ligament and deltoid ligament. Tibialis anterior and posterior muscles play an important role in raising the medial border of the arch, whereas flexor hallucis longus acts as bowstring.
Lateral Longitudinal Arch (LLA) – It is the lowest arch and compromises of calcaneus, cuboid and fourth & fifth metatarsal as its bony component. Like MLA the posterior pillar consists of tuberosity of calcaneus whereas the anterior pillar is formed by metatarsal heads of 4th and 5th metatarsals. Plantar aponeurosis, and long & short plantar ligaments provide support for LLA. Peroneus longus tendon plays an important role in maintaining the lateral border of the arch.
Transverse Arch – It is concave in non-weight bearing which runs medial to lateral in midtarsal and tarsometatarsal area. The bony component of the arch consists of metatarsal heads, cuboids and 3 cuneiform bones. The medial and lateral pillars of the arch is formed by medial and lateral longitudinal arch respectively. The arch is maintained by posterior tibialis tendon and peroneus longus tendon which cross the plantar surface from medial to lateral and lateral to medial respectively.
Windlass Mechanism of foot – The plantar aponeurosis acts similarly as windlass mechanism. Windlass is typically a horizontal cylinder that rotates with a crank or belt on a chain or rope to pull a heavy objects. The common use of windlass is seen in pulling the anchor of the ship known as anchor windlass. This mechanism can be seen in foot. When the MTP joints are hyperextended, the plantar aponeurosis becomes taut as it is wrapped around the MTP joints. This actions brings the metatarsal and tarsal bones together converting it into a rigid structure and eventually causing the longitudinal arches to rise. This function is important in providing a rigid lever for gait propulsion during push off.
Function of the Foot
The foot requires sufficient mobility and stability for all of its functions. Mobility is necessary for absorbing the ground reaction force of the body. Subtalar pronation has a shock absorbing effect during initial heel contact. Pronation is also necessary to make rotation of the leg possible and to absorb the impact of this rotation. Subtalar pronation plays a role in shock absorption through eccentric control of the supinators. On the other side, the joint of Chopart becomes unlocked so that the forefoot can stay loose and flexible. In midstance, the foot needs mobility to adapt to variation in surfaces.
Foot stability is necessary to provide a stable base for the body. The foot needs the capacity to bear body weight and act as a stable lever to propel the body in forward. This function requires pronation control of the subtalar joint.
Normal foot function provides the foot with the capacity to transform at the right time from a mobile adapter to a rigid lever. The foot needs sufficient mobility to move into all the positions of the gait cycle while maintaining mobility and stability. Physiological mobility is essential, because if mobility was too large, the foot would not have the capacity to be stable. When this condition is fulfilled, the joint can support standing in the stable maximally close packed position. When the normal transition of the two functions isn’t normal many overload injuries can be observed, like in the foot, under leg, upper leg but also in the lower back. Therefore the three phases of ground contact have to fall in the normal time interval, otherwise some compensation mechanisms (example: genu recurvatum in cases of reduced dorsiflexion) will be used, which cause overuse syndromes.(Example: chondromalacia, shinsplints...)
In the transition from midstance to propulsion phase, the mechanisms often fail. The transition from eversion to inversion is facilitated by the tibialis posterior muscle. The muscle is stretched like a spring and potential energy is stored. At the end of the midstance, the muscle passes from eccentric to concentric work and the energy is released. The tibialis posterior muscle then causes abduction and dorsiflexion of the caput tali in which the hindquarter everted. At the same time, the muscle peroneus longus, at the end of the midstance, will draw the forefoot with a plantar flexion of the first toe. This is how the forefoot becomes stable.
When the forefoot moves in the propulsion phase, the windlass phenomena starts. When the dorsiflexion of the metatarsophalangal joints begins the plantar fascia undergoes stress, so the os calcaneus becomes vertical and teared in inversion. Like this, the hindquarter rests in inversion in the unwinding of the forefoot.
When there are some abnormalities in the normal gait cycle of functions of the body, some functional ortheses can be used. This orthese have the capacity to correct the biomechanical function of the foot. In contrast, insoles only support the arch of the foot. Reduced or limited mobility in the lower limbs can be caused by a articular limitation. In these cases some classic mobilizations or mobilizations according to manual therapy can be designated. When the cause is a muscle shortening some stretching can be designated. Also, good (running) shoes are indicated.
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