Transmission of body weight onto the underlying surface: during the gait cycle and bipedal stand the construction of the foot absorbs shock and cushions the transfer of body load onto the underlying surface. The sole of the foot, a double angle lever, is perpendicular to the axis of the leg at rest and can distribute the weight of the body over a large surface.
Locomotion: the gait cycle is the most complicated pattern of movement in the musculoskeletal system, followed by full elevation of the arm and the biomechanics of the upper cervical spine. The foot’s function in the lower limb is to establish contact, support the weight of the body, adapt to uneven terrain, provide a stable supportive surface, and exercise propulsion. There are two different patterns in this activity:
In the landing phase (loading response) the foot performs a complete eversion movement (total pronation). The calcaneus moves into valgus and the forefoot (transverse tarsal joints) goes into extension, abduction, and pronation. The accompanying inward rotation of the talus then forces the tibia and later also the femur into accompanying inward rotation. This chain reaction begins at the calcaneus and ends approximately at T8.
Preparation for a chain reaction to introduce the push-off phase (total supination) begins proximally. The swing forward of the other leg causes a brief inward rotation of the hip joint in the stance leg that is transformed into outward rotation of the femur after absorption of the tension in the pelvitrochanteric muscles and the joint capsule. Finally, this femoral rotation pulls along the tibia and talus and the calcaneus responds with varus and inward rotation. The subsequent twisting makes the forefoot rigid and prepares it for load transfer as the calcaneus leaves the ground.
Sensory function: information from the many mechanoreceptors in joints, ligaments, and the sole of the foot contributes to the coordination of standing and walking as well as to the creation of equilibrium. Injuries to structures such as the deep intrinsic ligaments between talus and calcaneus in the tarsal sinus, resulting from inversion trauma, can lead to chronic pain and in particular to feelings of instability during heel contact (Helgeson, 2009; Karlsson et al., 1997).
Hand and foot skeletons have many parallel aspects in phylogenetic development. Thus, the transverse articulation in hand and foot—root, middle, and terminal elements—can be comparably described (Starck, 1978). In comparison to the construction of the skeleton of the hand, the tarsal bones stand out from their surroundings with their noticeable increase in bony mass and their reduced mobility.
The skeletal arches, also recognizable in the structure of the hand, are universally recognized to be more pronounced in the foot as longitudinal and transverse arches, with the median arch higher than the lateral. Phylogenetically, the calcaneus has developed from a flat position and has pulled the talus along with it into a vertical position. This created the longitudinal arches that transmit the weight of the body to the underlying surface not rigidly but with great elasticity. Through the plantar aponeurosis, the plantar ligaments (plantaris longus ligament), and the short foot muscles, the longitudinal arches are secured as with a tension band.
It is noteworthy that in the evolution of the metatarsal area, the first ray together with the ray of the great toe has rearticulated with the remaining metatarsal bones. This development improved the ability of the foot to both support the body and partake in heel-toe gait, but was at the cost of grasp, with enormous losses being made here in comparison to the feet of primates.
The angle between the skeleton of the foot and the axis of the leg in two directions is almost perpendicular and is labeled the “double-angled lever construction.” This enables locomotion on the soles of the feet and provides a long lever for the long muscles originating in the leg.
The talus has exceptional status. No muscles insert on it. All extrinsic tendons run past it, and no intrinsic tendons have their origin there. In a load-carrying situation, the talus distributes the body weight to the forefoot and heel. It functions as an adaptive intercalated segment (Landsmeer, 1961), comparable to the functioning of the carpal bones of the hand. In addition to contributing significantly to the extension and flexion capacity of the foot, the talus mediates rotation of the leg on the foot and vice versa.
The almost perpendicular relationship of the foot skeleton to the leg requires modification of the nomenclature for precise description of position and orientation of structures. As a result, a suggestion is offered for the following designations of position, so that the particular construction of the foot can be taken into account. The terms used above the talus are the usual ones; downward from the talus, the usual terminology is replaced by foot-specific terms. ▶ Fig. 7.1 indicates the boundary between the two terminologies with a transverse line through the talus.
An outstanding biomechanical characteristic in the foot is the formation of the kinematic complex consisting of the talocrural joint, the subtalar complex, and the transverse tarsal (TT) joint. This articular complex must always be viewed as a functional unit. The articular components always act together, especially during movement in a closed kinematic chain.
The transverse tarsal joint and its biomechanical connection to the ankle and talocalcaneonavicular (TCN) joints play another important role in the mobility and flexibility of the foot. Disorders within the kinematic chain—all of which lie along the Chopart (or TT) joint line—can only be identified using tests of joint play at the respective articulation.
The alignment of the subtalar complex during heel contact is decisive for the chain reaction from distal to proximal during the landing phase. The position and freedom of movement of the calcaneus determine further progress. For this reason, the subtalar complex is also known as a key joint.
The talus and calcaneus move in contrary motion, while the transverse tarsal joint always follows the movement of the calcaneus. In the landing phase, the calcaneus tips to the side in valgus position. Its distal end swings to lateral in abduction. At the same time, the talar head turns to medial, which is termed inward rotation or adduction. In inversion of the calcaneus in the push-off phase, the pattern of movement is the reverse for both; they press the distal tarsalia into a rigid position, which prepares them to take over the weight as the heel is lifted (▶ Fig. 7.2). The rotations of the talus and the lateral movements of the distal end of the calcaneus are often unrecognized and undervalued movement components that are essential for frictionless movement. In particular, the outward rotation of the talus is a decisive component that arises in association with most loaded flexion and extension positions of the talocrural joint (Van Langelaan, 1983; Huson, 1987, 2000; Lundberg, 1989).
The individual components of the motor complex influence each other and are always to be viewed, assessed, and, if necessary, treated as a unit when mobility is affected. Sites of hypomobility and hypermobility are often found adjacent to one another. Hence, all joints should be assessed individually in cases of abnormal mobility. Accurate knowledge of the position of the joint space is required to locate the respective joint.
Any dysfunction of sensation, mobility, and motor control in the foot affects the more superior sections of the lower limbs, the pelvis, and vertebral column. Therefore, particular attention should always be paid to symptoms of the foot.
▶ Arthritis. arthritis primarily has traumatic or rheumatic origins. Traumatic arthritis mainly develops following the common twisting the ankle trauma. The anterior talofibular ligament reinforcing the anterolateral aspect of the ankle joint capsule is one of the most commonly injured structures in the musculoskeletal system. Therapeutic management of this ligament injury requires:
▶ Restricted mobility. hypomobility in the ankle joint, usually resulting from immobilization or arthritis, is very common. The other aspects of the motor complex must be included in the examination of limited movement. The examination is based on things such as precise knowledge about the position and orientation of the articular space of the transverse tarsal joints.
▶ Laxities and instability. post-traumatic ligamentary tendon laxity in the talocrural joint is well known. The anterior ligaments of the ankle have the task of holding the tibia on the talus during weight-bearing. This can no longer be upheld in cases of extreme laxity, so that the tibia is no longer positioned to posterior over the center of the talus (Hintermann, 1999). During dorsiflexion in weight-bearing, dysfunctional arthrokinematics of the ankle can be confused with a restriction in mobility at the joint.
Other laxities may be hidden in the remaining components of the ankle, TCN, and TT (Chopart) joints’ kinematic complex. Traumatic injuries of the interosseous ligaments between talus and calcaneus can lead to tarsal sinus syndrome, in which patients report symptoms such as a feeling of instability in the hindfoot (Akiyama et al., 1999) especially on heel contact. Ligamentary laxity in the transverse tarsal joints stops the movement of the foot in the landing phase (total pronation) too late and causes hyperpronation of the foot in the middle of the stance phase.
In addition to ligamental injuries, inflammation of the Achilles tendon and synovial sheaths of the extrinsic (long) muscles of the foot is particularly painful. This can occur on both sides of the foot at the point where the extrinsic tendons change directions:
Narrowing of the tarsal tunnel, through which the flexor hallucis longus, flexor digitorum longus, and tibialis posterior also travel, mainly compresses the neural structure (Hudes, 2010). The tibial nerve divides into two plantar nerves after it exits the tunnel.
This nerve branch lies very close to the surface, anterolaterally and distally, on the leg. It crosses the talocrural joint medial to the malleolus fibularis. A possible injury can arise from overstretching in a sprain, from iatrogenic injury (Blair and Botte, 1994), or from irritation after carelessly executed transverse friction of the talofibular ligament.
Therapists should also be familiar with the bony construction of the foot and its individual sections, the joint lines, as well as the names of the individual tarsal bones and their mobile connections (▶ Fig. 7.3). Transverse subdivision of the foot skeleton into phalanges, metatarsus, and tarsus is certainly well known. The Lisfranc line, with its rather rigid joints, divides the metatarsus and the tarsus. The joints of the Chopart articular line (between talus and navicular bone medially and between the calcaneus and the cuboid laterally) are parts of the transverse tarsal articulations.
To emphasize the significance of the functional relationships in loaded foot movements, the participating joints are combined into the tibiotarsal complex (Padovani, 1975). This motor complex includes the talocrural joint, the subtalar complex (talocalcaneal joint) with two articular cavities, and the transverse tarsal joints. Functionally, the distal syndesmoses and the proximal tibiofibular joint are part of this complex.
These include the tendons and tendon sheaths of the long (extrinsic) foot muscles, especially as they pass by the tibiotarsal complex and their insertions. ▶ Fig. 7.4 shows the course to medial and plantar in the tarsal tunnel. This space provides a passageway for three tendons, two blood vessels, and the tibial nerve. It is covered by the retinaculum flexorum to become a tunnel. ▶ Fig. 7.5 depicts the particular course of the peroneal muscles with a frequently changing course of tendons behind the lateral malleolus, the peroneal trochlea, and at the cuboid bone (peroneus longus). The foot and toe extensors pass by the talocrural joint dorsally (▶ Fig. 7.6). The position of their tendons explains the secondary functions: the tibialis anterior and extensor hallucis longus adduct and supinate the foot, while the extensor digitorum longus with its branch (peroneus tertius), the only evertor of the foot, also abducts and pronates. All tendons of extrinsic muscles (except for the Achilles tendon) are held against the skeleton of the foot with retinacula, and for protection against friction require tendon sheaths that are several centimeters long.
The functionally and clinically important ligamentous apparatus of the foot is found extending laterally and medially from the malleoli (▶ Fig. 7.7 and ▶ Fig. 7.8). The talofibular ligaments control the position of the talar mortise, while the calcaneofibular tendon lies over the subtalar joints. The deltoid ligament is a coarse collagenous plate extending from the medial malleolus to the talus, calcaneus, and navicular bones. It is possible to see four separate ligaments in an anatomical preparation. This ligamentary complex appears much thicker and more stable than on the lateral aspect. The medial malleolus does not extend as far to plantar and, in addition, the ligamentary complex functions as a brake to pronation during the landing phase. The calcaneonavicular ligament closes the plantar articular space between talus, calcaneus, and navicular bones (calcaneonavicular ligament, spring ligament) and, together with other plantar ligaments and the short, intrinsic muscles, contributes to securing the medial longitudinal arch.
The tibial nerve passes on the medial side of the tarsal tunnel, divides into the medial and lateral plantar nerves and innervates the plantar intrinsic muscles. The possibility of compression neuropathy in the tunnel has already been noted. The deep and superficial peroneal (or fibular) nerves run dorsally on the foot. Whereas the deep branch innervates the dorsal intrinsic muscles, the superficial branches of the peroneal nerve are entirely sensory. They first emerge approximately 10 cm proximal to the talocrural joint under the fascia of the leg, divide into different branches, and run to the dorsum of the foot. The specific course of the cutaneus dorsalis intermedius will be described in chapter 7.4.
This is followed by the palpation of all joint spaces on the medial side and extends down onto the first metatarsophalangeal joint (▶ Fig. 7.9). It is advisable to review the directional terms for the leg and foot as given in ▶ Fig. 7.1 before beginning.
The patient sits in an elevated position, for example, on the edge of a treatment table. The therapist sits on a stool on the lateral side of the foot. The patient’s distal leg is placed on the therapist’s thigh to stabilize the leg while the foot itself is unsupported and can move freely (▶ Fig. 7.10).
This starting position (SP) is not mandatory when practicing palpation. The therapist can also choose to position the patient differently. The starting position described places the patient in a comfortable sitting position and gives the therapist the best possible access with both hands to the freely moving and almost neutrally positioned foot.
The posterior (facing the Achilles tendon) and plantar boundary of the medial malleolus should be palpated with the index finger from proximal and the anterior boundary and the transition to the articular space of the talocrural joint should be palpated with the index finger coming from distal (▶ Fig. 7.11).
In general, the boundaries are easy to access and can be marked clearly with transverse palpation. There is only one tendon that crosses a part of the edge and could somewhat impede palpation. The transition of the anterior edge to the talocrural articular space is not simple, since the tendon of the tibialis anterior hinders access to the tibialis anterior.
The therapist should avoid excessive prestretching of the medial soft tissues because the soft tissues can prevent free access to the bony edge of the medial malleolus if stretched. Checking the foot in mid-position of the joint is best done by using the hand coming from distal. When the edge of the medial malleolus is carefully followed, a little notch can be felt on the distal tip. This V-shaped notch separates the anterior portion of the medial malleolus (anterior colliculus) from the posterior portion (posterior colliculus) (Weigel and Nerlich, 2004).
The next bony structure is found approximately 1 cm inferior to the plantar tip of the malleolus: the sustentaculum tali. This is a bony eminence on the calcaneus that protrudes in a medial direction. The sustentaculum tali is quite interesting in terms of its topography and functional anatomy:
The therapist can access the inferior boundary by palpating the soft tissue from the sole of the foot toward the malleolus. The sustentaculum tali is the first osseous structure to be palpated that has a correspondingly hard feel (▶ Fig. 7.12).
The therapist gently places one finger between the inferior tip of the malleolus and the sustentaculum tali (that is, on the talus located underneath) to locate the rounded dorsal boundary and tilts the calcaneus medially (varus) and laterally (valgus) using small movements. In this way, it is possible to differentiate the sustentaculum tali, which is moveable, from the immovable talus.
The posterior and anterior boundaries of the sustentaculum tali are also identified. This structure appears to be approximately 1 cm wide and approximately 2 cm long in total (Olexa et al., 2000). Distally, the head of the talus, and proximally, the medial tubercle of the posterior talar process, articulate with it (▶ Fig. 7.14).
Palpating from the sustentaculum to distal, two bony eminences are encountered in rapid succession: the head of the talus and the tuberosity of the navicular bone. The head of the talus projects to medial directly next to the sustentaculum. If the tip of the palpating finger lies on the presumably correct spot, movement confirms the accurate location. For this purpose, the heel is tilted to medial and, if the subtalar biomechanics are normal, the head of the talus immediately turns away to lateral. Moving the calcaneus back to its former position allows the head to project to medial again.
If the therapist tilts the head of the talus by inverting the heel away to lateral, the distal boundary of the sustentaculum (palpation toward proximal) and the navicular tuberosity (still distinct) is reached in palpation toward distal.
Sections of the talus can be accessed from the anterior and posterior tips of the medial malleolus (▶ Fig. 7.13). Moving further distal from the anterior tip, the palpating finger immediately encounters the neck of the talus. The anterior-most portion of the deltoid ligament, the anterior tibiotalar ligament, inserts here. The posterior articular surfaces directly proximal to the malleolus are less distinctly felt. They lie directly above the posterior process of the posterior talar process.
The palpating finger applies moderate pressure to the posterior tip of the medial malleolus and gradually moves posterior and slightly inferior. Palpating to proximal from the sustentaculum is also a successful way of finding the tubercle. With circular palpation, the tubercle is found as another bony eminence (see ▶ Fig. 7.14). Another section of the deltoid ligament inserts here—the posterior tibiotalar part.
Movement is used to confirm the definite identity of this structure. The free hand facilitates alternating ankle dorsiflexion and plantar flexion. The posterior process of the talus increasingly pushes against the palpating finger during dorsiflexion and disappears into the tissues during plantar flexion. This results from the rolling and gliding motion of the talus during this movement and the associated changes in spatial position.
This is the most prominent tendon on the medial side. It is one of the tendons held on the foot and the skeleton of the leg by the flexor retinaculum. The extraordinary feature of its course is its position in a deep, separate groove (sulcus tendinis of the posterior tibial muscle) (von Lanz and Wachsmuth, 2003) on the medial malleolus, just under the flexion-extension axis of the talocrural joint.
Theoretically, the tendon can be found using a flat, transverse palpation technique, even when it is relaxed, over the malleolus. Practically, this often proves difficult (▶ Fig. 7.15).
The tendon is made more distinct for palpation by isometrically or rhythmically contracting the muscle with inversion of the foot (plantar flexion, adduction, and supination). This allows the tendon to be traced over its entire length, from the distal leg to its primary insertion on the navicular tuberosity.
Following the tendon of the posterior tibial muscle systematically to distal, one reaches a bony eminence, the tuberosity of the navicular bone, whose size can be observed with rounded, circular palpation. To locate this structure precisely, the muscle should be relaxed and the tendon free of tension. The tuberosity presents as a distinct, rounded elevation. It feels hard when pressure is applied. In contrast, the tendon reacts with slightly more elasticity. To differentiate it from the head of the talus, which is also projecting in the close vicinity, the heel is tipped to medial, causing the head of the talus to swing to lateral and emphasize the proximal boundary of the navicular. The talonavicular articular space is found at this point. The extent of the tuberosity can be felt at the medial edge of the foot and also on the sole, by means of circular palpation.
The sections of the deltoid ligament and the plantar calcaneonavicular ligament are the most important ligaments on the medial side of the foot (see ▶ Fig. 7.8).
The individual ligaments of the deltoid ligament cannot be located by palpation. Their fibers flow together and there are too many other soft-tissue elements lying above them to permit direct contact (retinaculum flexorum and various tendons).
For example, the therapist comprehends that the posterior tibiotalar ligament is placed under more tension as dorsiflexion of the ankle increases (▶ Fig. 7.16). The medial tubercle of the posterior process of the talus projects proximal and plantar and moves away from the medial malleolus. This tightens the ligament and supports the approximation of the articulating bones in the ankle.
The plantar calcaneonavicular ligament passes underneath the head of the talus between the sustentaculum tali and the navicular tuberosity. It is palpable as a thick, rounded structure and converges with the tibialis posterior tendon onto the tuberosity.
The boundary with the neighboring bony fixed points is confirmed by moving the heel (with forefoot). The pad of the finger lies on the medially accessible aspect of the talar head between the sustentaculum and the navicular tuberosity. The fingertip points to plantar (▶ Fig. 7.17). When the heel is tilted to medial, the head disappears to lateral. Distally and proximally, the neighboring bony features become distinctly palpable. With pressure to lateral, the fingertip can hit the spring ligament. A pronounced lateral tilt of the heel causes the head of the talus to project to medial, thus tightening the ligament.
This is the second tendon that, together with its tendon sheath, passes through the tarsal tunnel under the deep lamina of the retinaculum flexorum. Like the tendon described below, it can only be distinctly detected proximal to the talus and calcaneus.
As this area is often filled with fatty tissue, it is unlikely that the tendon can be located using transverse palpation alone. The therapist therefore uses active and rhythmical toe flexion to confirm the correct location. Now, the increase and decrease in tension in the tendon is rather distinct. If this is not successful, the tension in the tendon can also be increased, in order to feel it more clearly, by passive extension of the toes.
The next tendon and its synovial sheath are palpated using the same method. This tendon is found immediately posterior to the above-described tendons and is the third tendon held on the skeleton of the leg and foot by the flexor retinaculum. To plantar, the tendon continues in its own tibial groove and further on, between the two tubercles of the posterior talar process.
Starting at the tendon of flexor digitorum longus, palpation again moves slightly more posteriorly toward the Achilles tendon (▶ Fig. 7.20 and ▶ Fig. 7.21). The tendon of the flexor hallucis longus is palpated as the last firm and elastic structure before the Achilles tendon. The location is confirmed here using rhythmical active flexion of the first toe. Passive extension of the great toe also produces the desired tension of the tendon, which allows it to be more easily found. By transverse palpation, it is possible to follow the tendon in a plantar direction as far as directly proximal to the medial tubercle.
In addition to the three tendons and synovial sheaths described above, three structures pass between the deep and superficial laminae of the retinaculum flexorum (von Lanz and Wachsmuth, 2003) behind the medial malleolus to the sole of the foot (▶ Fig. 7.22):
The posterior process of the talus is located first. From this point palpation moves somewhat proximal and the therapist applies one finger pad flat, with little pressure. von Lanz and Wachsmuth (2003) describe its position as follows: “The pulse of the posterior artery can be felt in the medial malleolar groove, approximately halfway between medial malleolus and the Achilles tendon.”
After a short time of flat and patient palpation, the pulsation of the artery is felt. It can be followed for a short distance to proximal. In approximately 72% of the subjects studied by Yang et al. (2017), the bifurcation points of the artery were located within the tarsal tunnel.
Directly next to the artery lies the tibial nerve, which passes through the tarsal tunnel and then divides into two branches (plantar nerves, Yang et al., 2017). The therapist attempts to identify the nerve by hooking around it (like with a guitar string), using a pointed palpation technique perpendicular to the structure. The nerve rolls away underneath the palpating finger when it has been exactly located. It is not possible to precisely identify the vein using palpation.
The palpation leaves the medial malleolus and concentrates on other structures on the medial side of the foot. The tendon of the anterior tibial muscle is a landmark for finding articular spaces on the medial edge of the foot.
The wide tendon of the tibialis anterior can be clearly demonstrated using dorsiflexion, adduction, and supination of the foot to contract the muscle (▶ Fig. 7.23). Its edges can be marked without any difficulty and followed distally down onto the medial edge of the foot. The tendon widens here, flattens, and eludes further palpation. This is the location of the joint space between the medial cuneiform and the base of the first metatarsal (MT).
The proximal edge of the retinaculum flexorum is palpable. The starting point is a location directly plantar and proximal to the medial tuberosity of the posterior process of the talus that can be palpated with a fingertip directed toward plantar and distal. When deep pressure is applied, the fingertip slides in a somewhat plantar and distal direction until a firm elastic edge can be distinctly felt. This edge becomes taut when the heel is everted (▶ Fig. 7.24).