Anatomy and Kinesiology
The Talocrural Joint
The interosseous membrane of the leg extends over the entire length between the tibia and the fibula. Distally, the tibia and fibula are firmly held together by stiff collagenous connective tissue (tibiofibular syndesmosis). On both the anterior side (anterior tibiofibular ligament) and the posterior side (posterior tibiofibular ligament), this connection is strengthened.
Between the distal part of the fibular diaphysis and the distal tibial epiphysis, there is a protrusion of the joint cavity of the talocrural joint. The talocrural joint is formed by the trochlea of the talus and the distal extremities of the fibula and the tibia. On the medial side of the talocrural joint is the deltoid ligament, that radiates in four parts from the medial malleolus. On the lateral side, the anterior talofibular ligament proceeds from the front of the lateral malleolus to the neck of the talus and from the posterior side of the lateral malleolus the posterior talofibular ligament proceeds to the dorsal side of the talus [Figure 88]. The lower edge of the lateral malleolus is connected by the calcaneofibular ligament to the lateral side of the calcaneus.
Figure 88: Ligaments of the Right Ankle and Foot (Lateral View)
1 Anterior talofibular ligament.
2 Posterior talofibular ligament.
3 Bifurcate ligament.
4 Calcaneofibular ligament.
5 Anterior tibiofibular ligament.
6 Posterior tibiofibular ligament.
7 Interosseous talocalcaneal ligament.
From a morphological viewpoint, the ankle joint is considered to be a hinged joint even though in terms of function, it is more similar to a saddle joint, with the most important movement possibilities, from the neutral position, being [Figure 89]:
- Dorsal flexion (about 20°).
- Plantar flexion (about 50°).
Figure 89: Movements of the Ankle and Foot
A = Pronation-supination axis.
B = Dorsal-plantar flexion axis.
C = Inversion-eversion axis.
In addition to this, small rotational and side-to-side tipping movements are possible (assuming the neutral position).
The trochlea of the talus is broader on the ventral side than the dorsal side. In the case of dorsal flexion, the broader ventral part of the trochlea of the talus comes to lie within the ‘tibiofibular fork.’ In maximum dorsal flexion, the trochlea of the talus ‘pushes’ both distal extremities of the tibia and the fibula to a maximum of up to 2 mm apart from each other. In this position, the only movement permitted in the talocrural joint is plantar flexion. In the maximum plantar flexion position, the narrower dorsal part of the trochlea of the talus is located in the ‘tibiofibular fork.’ In this position, some lateral ‘sliding movements’ (or adduction and abduction) or rotation around a longitudinal axis is possible via the lower leg in the talocrural joint.
The Subtalar Joint
The subtalar joint, formed by the talus and the calcaneus; and the talocalcaneonavicular joint, formed by the talus, calcaneus and the navicular bone, together form the subtalar joint. They are divided into an anterior chamber and a posterior chamber by the tarsal sinus. This subtalar joint is bridged by various ligamentous structures. In the tarsal sinus, there is the strong interosseus talocalcaneum ligament, which connects the base of the talus with the top of the calcaneus (between the anterior and the posterior compartments). The ‘socket’ of the anterior compartment is, amongst others, formed by the socket-shaped joint surfaces of the navicular bone and the calcaneus.
The other part of the socket is formed by a strong ligament, the plantar calcaneonavicular ligament. The side of this ligament that faces the joint cavity is formed from disc-like, stiff collagenous connective tissue. The talus head is the ball that fits inside this socket.
The posterior compartment of the subtalar joint is a saddle joint. The construction of both compartments, with the interosseous talocalcaneal ligament in between, only permits movement around a single axis [Figure 89]:
- Inversion (about 5°) (the base of the bone turns to the medial surface).
- Eversion (about 5°) (the base of the bone faces away from the medial surface). The link prevents movement around other axes that should, in principle, be possible in an ellipsoid joint or saddle joint. The interosseous talocalcaneal ligament functions as a type of ‘cruciate ligament’ (compare with the knee) of the subtalar joint.
The talus and the calcaneus, together with the navicular bone, the cuboid bone and the 3 cuneiform bones form the tarsal bones (tarsus or root of the foot) [Figure 90]. The other intertarsal articulations only possess a very slight mobility. The tarsals are interconnected by strong ligaments. These ligaments are not discussed here. The joints, formed by the joint spaces between the talus and the navicular bone on the one side, and the calcaneus and the cuboid bone on the other, are jointly referred to as the transverse tarsal joint (Chopart’s joint).
Figure 90: Dorsal View of the Right Foot Skeleton
1 Calcaneal tuberosity.
2 Calcaneus.
3A Trochlea of the talus.
3B Neck of talus.
3C Head of talus.
4 Navicular bone.
5 Cuboid bone.
6 Medial cuneiform bone.
7 Intermediate cuneiform bone.
8 Lateral cuneiform bone.
9 Tuberosity of metatarsal V.
10 Metatarsal bone.
11 Proximal phalanx.
12 Medial phalanx.
13 Distal phalanx.
Black Arch: Transverse tarsal joint.
The Tarsometatarsal Articulations
The joint surfaces between the distal tarsae (cuboid bone and cuneiform bone) together with the corresponding joint surfaces of the metatarsals (tarsometatarsal articulations), form the Lisfranc joint. The mobility in this joint is greater than in the homologous carpometacarpal joints of the hand. Three joint capsules and various ligament structures strengthen the three separate joint cavities.
These three joint cavities are localised:
- Between the medial cuneiform bone and the first metatarsal bone.
- Between the intermediate and lateral cuneiform bones and the second and third metatarsal bones.
- Between the cuboid bone and the fourth and fifth metatarsal bones.
The metatarsals form the mid-foot or metatarsus. The second, third, fourth and fifth metatarsals also articulate distally with respect to each other on the sides via flat joint facets. The joint capsules are strengthened by dorsal and plantar ligaments. Two sesamoid bones are located under the head of the first metatarsal bone. These can also incidentally occur in other toes.
The movement possibilities in the midfoot and forefoot are [Figures 89, 91].
- Supination.
- Pronation.
Figure 91: Pronation and Supination Movements of the Foot
A = Pronation.
B = Supination.
Due to the abduction and adduction components, these two movements can only be examined passively. In the literature, there is no unequivocal definition of pronation and supination and inversion and eversion. In our view, pronation and supination take place in the longitudinal plane of the foot’s ‘axis.’ During supination, the medial side of the forefoot is directed in the dorsal direction and the lateral side in the plantar direction; in the case of pronation, the opposite is true. No clear pronation/supination axis can be described (as is the case for the forearm).
Pronation and supination arise due to the ‘twisting’ of the mid-foot and forefoot with respect to the root of the foot; during this the calcaneus should be stabilised by the examiner.
The Metatarsophalangeal Articulations and the Interphalangeal Articulations
The movement possibilities of these joints are namely:
- Flexion.
- Extension.
The toes are part of the forefoot, which are important for the foot-floor contact pattern. The heads of the metatarsal bones are also usually considered to be part of the forefoot. These joints are also strengthened by a large number of superficially-located ligaments.
The Medial Longitudinal Arch of the Foot
The bones on the medial side as well as a number of ligaments (including the plantar fascia) and muscles (including the plantar flexors) cause a slight arch along the medial side of the foot. Various muscles act as arch tensors in this arch. The arch functions as a shock absorber, essential for ensuring a smooth gait.
The Transverse Arch of the Forefoot
This arch is mainly formed by the heads of the metatarsals; the head of the second metatarsal bone should be the furthest from the ground. In the case of a sunken, flat forefoot an excessive layer of calloused skin is seen under the heads of the metatarsals that are positioned too low (in particular II and III). In the case of a well-built foot, some calloused skin might be seen under the heel, the lateral foot edge and under the ball of the foot (the first metatarsophalangeal joint, MTP-I joint).
The Muscles of the Lower Leg, Foot and Ankle
The most important muscles of the lower leg, foot and ankle are:
- Tibialis anterior muscle (especially dorsal flexion and inversion and eversion of the foot, depending on the position of the foot in the subtalar joint).
- Extensor digitorum longus muscle (in particular dorsal flexion and extension of digits 2 to 5).
- Extensor hallucis longus muscle (especially dorsal flexion of the foot and extension of digit 1).
- Extensor digitorum brevis muscle (in particular extension of MTP-II to MTP-IV).
- Extensor hallucis brevis muscle (in particular extension of MTP-I).
NB: The muscle belly of these last two muscles is mostly visible as a (sometimes blue) swelling shining through on the lateral side of the dorsum of foot, distal from the tarsal sinus, and is sometimes wrongly believed to be a traumatic swelling. - Tibialis posterior muscle (in particular plantar flexion and inversion of the foot).
- Flexor digitorum longus muscle (in particular plantar flexion of the foot and flexion of digits 2 to 5).
- Flexor hallucis longus muscle (in particular plantar flexion of the foot and flexion of digit 1).
- Triceps surae muscle (gastrocnemius muscle, soleus muscle and plantaris muscle) (in particular plantar flexion of the foot).
NB: Some authors do not consider the plantaris muscle to be part of the triceps surae muscle. - Peroneus longus muscle and peroneus brevis muscle (in particular plantar flexion and eversion of the foot).
A number of short muscles are located in the plantar side of the foot. These are not discussed here as they are not accessible for physical-diagnostic examination.
Connective Tissue, Retinacula and Tendon Sheaths
The muscles of the lower leg are surrounded by the crural fascia and are divided into the following groups by the intermuscular septa:
- Ventral Group: Tibialis anterior muscle, extensor digitorum longus muscle and extensor hallucis longus muscle.
- Lateral Group: Peroneus longus and brevis muscles.
- Dorsal Group; these can in turn be subdivided into:
- Superficial Group: Triceps surae muscle (gastrocnemius muscle and soleus muscle) and plantaris muscle.
- Deep Group: Tibialis posterior muscle, flexor digitorum longus muscle and flexor hallucis longus muscle (popliteal muscle).
NB: In particular, the muscle bellies of the muscles in the ventral group and the lateral group are located in separate chambers or compartments. The walls of these compartments are formed by the crural fascia, the previously-mentioned intermuscular septa, tibial and fibular periosteum and the interosseous membrane. These walls serve as a proximal site of attachment for the muscles of these groups.
The long tendons of the lower leg and foot muscles are held in place at the ankle by the following retinacula:
- Two retinacula of extensor muscles, which are situated transversely above and below the talocrural joint and fix the tendons of the extensors.
- The retinculum of the flexor muscles, which proceeds form the medial malleolus to the calcaneus and fixes the tendons of the deep flexors (including the tibialis posterior muscle).
- The superior peroneal retinaculum, which proceeds from the lateral malleolus to the calcaneus, and the inferior peroneal retinaculum that is extended between the lateral side of the talus and the calcaneus. Both fix the tendons of the peroneus longus and peroneus brevis muscles.
At the level of the various retinacula, there are various tendons surrounded by tendon sheaths. The tendons of the tibialis anterior muscle, the extensor hallucis longus muscle and the extensor digitorum longus muscle are each surrounded by their own tendon sheath. The tendons of the tibialis posterior muscle, flexor digitorum longus muscle and the flexor hallucis longus muscle also each possess their own tendon sheath. The peroneus longus and brevis muscles have their own tendon sheaths distally, yet at the height of the lateral malleolus these usually transition into a joint sheath. In the case of an avulsion fracture, a haemotoma is often seen to develop in the tendon of the peroneus brevis muscle which extends proximally via the communal tendon sheath.
The space behind and on the plantar side of the medial malleolus is termed the tarsal tunnel. The roof of this tunnel, which lies just below the surface, is formed by the retinaculum of the flexor muscles. This tunnel contains the tendons of the tibialis posterior muscle, flexor digitorum longus muscle and flexor hallucis longus muscle, the posterior tibial arteries and veins and the tibial nerve or its continuations: the medial plantar nerve and the lateral plantar nerve. Runners in particular are susceptible to impingement of the tibial nerve in this tunnel, which may lead to (radiating) pain in the heel or sole of the foot and possibly a loss of sensitivity.
Terminology
Neutral Position
This is the position in which the sole of the foot forms an angle of 90° with the lower leg.
Shaft
Imaginary longitudinal axis through a toe and the associated metatarsal bone proximally extended to the root of the foot. The first shaft runs proximally though the digit 1, the fifth shaft runs proximally through digit 5.
Aponeurosis
Flat layers of tendon tissue made up of stiff collagen connective tissue. It usually covers muscles; on the side facing the muscle tissue muscle fibre bundles are attached to it.
Plantar Fascia
Aponeurosis or layers of tendons in the sole of the foot, running from the calcaneal tuberosity and the base of the proximal phalanges.
Syndesmosis
Connective tissue-like connection between two bones.
Compartment Syndrome
Syndrome in which the circulation and function of muscle tissues in an enclosed space are disrupted as a consequence of increased pressure in this space.
Shin Splints, or Tibial Stress Syndrome
This is understood to mean tendonosis or inflammation of the periosteum of the tibialis posterior muscle, flexor digitorum longus muscle and/or flexor hallucis longus muscles and sometimes the soleus muscle as well, at their origin in the tibia.
Synovial Impingement
Hyperplastic and fibrotic synovium (synovial membrane of the joint capsule), mostly secondary to a lateral ankle ligament injury, characterised by pain and symptoms of impingement.
Pes Planotransversus
Sunk transverse foot arch (transition between midfoot/forefoot), characterised by all distal extremities of the metatarsal bones making contact with the ground in the standing position (normally the distal extremities of metatarsal bones II and III do not do this). As a result of this the toes are usually spread apart slightly. Callous formation is therefore seen under all distal extremities of the metatarsal bones.
Curved Toe
Congenital abnormality that usually concerns digit 4 and/or 5. The distal phalanx is in adduction, flexion and is rotated.
Hammer Toe
Acquired abnormality. The MTP joint is in extension, the proximal interphalangeal (PIP) joint is in flexion and the distal interphalangeal (DIP) joint is in the normal extension position.
Clawed Toe
Acquired abnormality. The MTP joint is in (hyper) extension and the PIP and DIP joints in flexion, as a result of which the toe no longer makes contact with the ground.