ankle and foot biomechanics 1- structure
TRANSCRIPT
Biomechanics of the Ankle and Foot Complex : 1
Dr. Dibyendunarayan Bid [PT]The Sarvajanik College of Physiotherapy, Rampura, Surat
Introduction
The ankle/foot complex is structurally analogous to the wrist-hand complex of the upper extremity but has a number of distinct differences to optimize its primary role to bear weight. The complementing structures of the foot allow the foot to sustain large weightbearing stresses under a variety of surfaces and activities that maximize stability and mobility.6/18/2012 [email protected] 2
The ankle/foot complex must meet the stability demands of: (1) providing a stable base of support for the body in a variety of weight-bearing postures without excessive muscular activity and energy expenditure and (2) acting as a rigid lever for effective push-off during gait.
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The stability requirements can be contrasted to the mobility demands of: (1) dampening rotations imposed by the more proximal joints of the lower limbs, (2) being flexible enough to absorb the shock of the superimposed body weight as the foot hits the ground, and (3) permitting the foot to conform to a wide range of changing and varied terrain.
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The ankle/foot complex meets these diverse requirements through the integrated movements of its 28 bones that form 25 component joints. These joints include: the proximal and distal tibiofibular joints; the talocrural, or ankle, joint; the talocalcaneal, or subtalar, joint; the talonavicular and the calcaneocuboid joints (transverse tarsal joints); the five tarsometatarsal joints; five metatarsophalangeal joints; and nine interphalangeal joints.6/18/2012 [email protected] 5
Anatomy Of The Foot & Anklehttp://www.youtube.com/watch?v=c7QewW3Up50
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To facilitate description and understanding of the ankle/foot complex, the bones of the foot are traditionally divided into three functional segments.
These are:
the hindfoot (posterior segment), composed of the talus and calcaneus; the midfoot (middle segment), composed of the navicular, cuboid, and three cuneiform bones; and the forefoot (anterior segment), composed of the metatarsals and the phalanges (Fig. 121).6/18/2012 [email protected]
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These terms are commonly used in descriptions of ankle or foot dysfunction or deformity and are similarly useful in understanding normal ankle and foot function.
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The frequency of problems can be complex structure participation in activities.
many ankle or foot traced readily to the of the foot and their all weight-bearing
Structural abnormalities can lead to altered movements between joints and contribute to excessive stresses on tissues of the foot and ankle that result in injury.6/18/2012 [email protected]
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Definitions of Motions
A unique set of terms is used to refer to motion of the foot and ankle. The same terms are used at most of the joints of the ankle and foot, and, consequently, it is useful to describe them at the outset.
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As we have seen at other joint complexes, few if any of the joint axes lies in the cardinal planes; more commonly, the joint axes are oblique and cut across all three planes of motion.
The obliquity of the axes and implications for motion and function will be described in detail as we6/18/2012 [email protected] 12
The three motions of the ankle/foot complex that approximate cardinal planes and axes are: dorsiflexion/plantarflexion, inversion/eversion, and abduction/adduction (Fig. 12-2).
Dorsiflexion and plantarflexion are motions that occur approximately in the sagittal plane around a coronal axis. Dorsiflexion decreases the angle between the leg and the dorsum of the foot, whereas plantarflexion increases this angle.6/18/2012 [email protected] 13
At the toes, motion around a similar axis is termed extension (bringing the toes up), whereas the opposite motion is flexion (bringing the toes down or curling them).
Inversion and eversion occur approximately in the frontal plane around a longitudinal (anteroposterior [A-P]) axis that runs through the length6/18/2012 [email protected] 14
Figure 12-2 Cardinal axes for the motions of the ankle/foot complex.
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Inversion occurs when the plantar surface of the segment is brought toward the midline; eversion is the opposite. Abduction and adduction occur approximately in the transverse plane around a vertical axis. Abduction is when the distal aspect of a segment moves away from the midline of the body (or away from the midline of the foot in the case of the toes); adduction is the opposite.6/18/2012 [email protected] 16
Pronation/supination in the foot are motions that occur around an axis that lies at an angle to each of the axes for cardinal motions of dorsiflexion/plantarflexion, inversion/eversion, and abduction/adduction.
Consequently, pronation and supination are terms used to describe composite motions that have components of, or are coupled to, each of the cardinal motions.6/18/2012 [email protected] 17
Pronation is motion about an axis that results in coupled motions of dorsiflexion, eversion, and abduction.
Supination is a motion about an axis that results in coupled motions of plantarflexion, inversion, and adduction.
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The proportional contribution that each of the coupled motions makes to pronation/supination is dependent on and varies with the angle of the pronation/supination joint axis.
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Valgus and varus are terms that may be used for the ankle/foot complex in several ways, depending on the context. The definitions that we used throughout discussion of other joints in other chapters will not change. That is, valgus refers to a reduction in the medial angle between two bones (or movement of the distal segment away from the midline); varus refers to the opposite.6/18/2012 [email protected] 20
However, valgus and varus are sometimes used to refer to fixed deformities in the ankle/foot complex, whereas at other times the terms are used to describe or as synonyms for other normal motions.
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An example of common usage is to describe the fixed or weight-bearing position of the posterior calcaneus in relation to the posterior midline of the leg, with an increase in the medial angle between the two reference lines being valgus of the calcaneus (or calcaneovalgus) and a decrease being varus of the calcaneus (or calcaneovarus) (Fig. 12-3).6/18/2012 [email protected] 22
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Ankle Joint
The term ankle refers specifically to the talocrural joint: that is, the articulation between the distal tibia and fibula proximally and the body of the talus distally (Fig. 12-4).
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The ankle is a synovial hinge joint with a joint capsule and associated ligaments.
It is generally considered to have a single oblique axis with one degree of freedom around which the motions of dorsiflexion/ plantarflexion occur.
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Ankle Joint Structure
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Proximal Articular Surfaces
The proximal segment of the ankle is composed of the concave surface of the distal tibia and of the tibial and fibular malleoli. These three facets form an almost continuous concave joint surface that extends more distally on the fibular (lateral) side than on the tibial (medial) side (see Fig. 12-4) and more distally on the posterior margin of the tibia than on the anterior margin. The structure of the distal tibia and the malleoli resembles and is referred to as a mortise. 6/18/2012 [email protected]
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A common example of a mortise is the gripping part of a wrench. Either the wrench can be fixed (fitting a bolt of only one size) or it can be adjustable (permitting use of the wrench on a variety of bolt sizes). The adjustable mortise is more complex than a fixed mortise because it combines mobility and stability functions.
The mortise of the ankle is adjustable, relying on the proximal and distal tibiofibular joints to both permit and control the changes in the mortise.
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The proximal and distal tibiofibular joints (Fig. 12-5) are anatomically distinct from the ankle joint, but these two linked joints function exclusively to serve the ankle. Unlike their upper extremity counterparts, the proximal and distal radioulnar joints, the tibiofibular joints do not add any degrees of freedom to the more distal ankle and foot.
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However, fusion of the radioulnar joints would have little effect on wrist range of motion (ROM), whereas fusion of the tibiofibular joints may impair normal ankle function by limiting the ability of the talus to move within the ankle mortise.
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Proximal Tibiofibular Joint
The proximal tibiofibular joint is a plane synovial joint formed by the articulation of the head of the fibula with the posterolateral aspect of the tibia. Although the facets of the proximal tibiofibular joint are fairly flat and vary in configuration among individuals, a slight convexity of the tibial facet and a slight concavity of the fibular facet seem to predominate. The inclination of the facets may vary from nearly vertical to nearly horizontal in orientation.6/18/2012 [email protected] 33
Each proximal tibiofibular joint is surrounded by a joint capsule that is reinforced by anterior and posterior tibiofibular ligaments. Most typically, the proximal tibiofibular joint is anatomically separate from the knee joint.
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Motion at the proximal tibiofibular joint is variable but consistently small; it has been described as superior and inferior sliding of the fibula and as fibular rotation. The relevance of motion at the proximal and distal tibiofibular joints will be seen when the ankle joint motion is discussed.6/18/2012 [email protected] 35
Distal Tibiofibular Joint
The distal tibiofibular joint is a syndesmosis, or fibrous union, between the concave facet of the tibia and the convex facet of the fibula. The distal tibia and fibula do not actually come into contact with each other but are separated by fibroadipose tissue.6/18/2012 [email protected] 36
Although there is no joint capsule, there are several associated ligaments at the distal tibiofibular joint.
Because the proximal and distal joints are linked (the tibia, fibular, and tibiofibular joints are part of a closed chain), > all the ligaments that lie between the tibia and fibula contribute to stability at both joints.6/18/2012 [email protected] 37
The ligaments of the distal tibiofibular joint are primarily responsible for maintaining a stable mortise.
The ligamentous structures that support the distal tibiofibular joint are the anterior and posterior tibiofibular ligaments and the interosseous membrane.6/18/2012 [email protected] 38
The interosseous membrane directly supports both proximal and distal tibiofibular articulations.
The distal tibiofibular joint is an extremely strong articulation.
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Stresses that tend to move the talus excessively in the mortise (e.g., falling onto the side of the foot) often tear an ankle collateral ligament before the tibiofibular ligaments. Continued force may fracture the fibula proximal to the distal tibiofibular ligaments before the tibiofibular ligaments will tear.6/18/2012 [email protected] 40
The function of the ankle (talocrural) joint is dependent on stability of the tibiofibular mortise. The tibia and fibula would be unable to grasp and hold on to the talus if the tibia and fibular were permitted to separate or if one side of the mortise were missing. The analogous mortise of a wrench could not perform its function of grasping a bolt if the two pincer segments moved apart every time a force was applied to the wrench.6/18/2012 [email protected] 41
Conversely, the ankle mortise must have some mobility function to serve; otherwise, a single fused arch would better serve ankle joint function.
The mobility role of the mortise belongs primarily to the fibula.The fibula has, in fact, little weightbearing function; no more than 10% of the weight that comes through the femur is transmitted through the fibula.6/18/2012 [email protected] 42
Given the relatively small weight-bearing function of the fibula, the hyaline cartilage of the synovial proximal tibiofibular joint appears to be dependent on joint motion (rather than weight-bearing) to maintain nutrition of the cartilage. That is, the proximal tibiofibular joint must be mobile; if the proximal tibiofibular joint is mobile, so too must the distal tibiofibular joint be, because the two joints are mechanically linked.6/18/2012 [email protected] 43
Distal Articular Surface
The body of the talus (Fig. 12-6) forms the distal articulation of the ankle joint. The body of the talus has three articular surfaces: a large lateral (fibular) facet, a smaller medial (tibial) facet, and a trochlear (superior) facet.
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The large, convex trochlear surface has a central groove that runs at a slight angle to the head and neck of the talus. The body of the talus also appears wider anteriorly than posteriorly, which gives it a wedge shape.
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The degree of wedging may vary among individuals, with no wedging at all in some and a 25% decrease in width anteriorly to posteriorly in others. The articular cartilage covering the trochlea is continuous with the cartilage covering the more extensive lateral facet and the smaller medial facet.
The structural integrity of the ankle joint is maintained throughout the ROM of the joint by a number of important ligaments.6/18/2012 [email protected] 46
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Capsule and Ligaments
The capsule of the ankle joint is fairly thin and especially weak anteriorly and posteriorly. Therefore, the stability of the ankle depends on an intact ligamentous structure. The ligaments that support the proximal and distal tibiofibular joints (the crural tibiofibular interosseous ligament, the anterior and posterior tibiofibular ligaments, and the tibiofibular interosseous membrane) are important for stability of the mortise and, therefore, for stability of the ankle.6/18/2012 [email protected] 48
Two other major ligaments maintain contact and congruence of the mortise and talus and control medial-lateral joint stability. These are the medial collateral ligament (MCL) and the lateral collateral ligament (LCL).
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Both of these ligaments also provide key support for the subtalar (or talocalcaneal) joint that they also cross. The function of the collaterals at the ankle joint, therefore, are difficult to separate from the function at the subtalar joint.
Portions of the extensor and peroneal retinaculae of the ankle are also credited with contributing to stability at the ankle joint.6/18/2012 [email protected] 50
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The MCL is most commonly called the deltoid ligament. As its name implies, the deltoid ligament is a fanshaped.
It has superficial and deep fibers that arise from the borders of the tibial malleolus and insert in a continuous line on the navicular bone anteriorly and on the talus and calcaneus distally and posteriorly (Fig. 12-7).The deltoid ligament as a whole is extremely strong.6/18/2012 [email protected] 52
Valgus forces that would open the medial side of the ankle may actually fracture and displace (avulse) the tibial malleolus before the deltoid ligament tears. This ligament helps control medial distraction stresses on the ankle joint and also helps check motion at the extremes of joint range, particularly with calcaneal eversion.6/18/2012 [email protected] 53
The LCL is composed of three separate bands that are commonly referred to as separate ligaments. These are the anterior and posterior talofibular ligaments and the calcaneofibular ligament (Fig. 12-8). The anterior and posterior ligaments run in a fairly horizontal position, whereas the longer calcaneofibular ligament is nearly vertical.6/18/2012 [email protected] 54
The LCL helps control varus stresses that result in lateral distraction of the joint and helps check extremes of joint ROM, particularly calcaneal inversion. In general, the components of the LCL are weaker and more susceptible to injury than are those of the MCL. As a result, the relative contributions of the LCL to ankle stability have been studied extensively, with (as we often find) some differing conclusions.6/18/2012 [email protected] 55
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The inferior extensor retinaculum (Fig. 12-9) may also contribute to stability of the ankle joint.
Two additional structures that lie close and parallel to the calcaneofibular ligament appear to reinforce that ligament and serve a similar function.
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These are the inferior band of the superior peroneal retinaculum (see Fig. 12-9) and the much more variable lateral talocalcaneal ligament. The ankle collateral ligaments and the retinaculae also contribute to stability of the subtalar joint and will be discussed again in that context.6/18/2012 [email protected] 58
The ankle joint classically is considered to have one degree of freedom, with dorsiflexion/plantarflexion occurring between the talus and the mortise. At the ankle, dorsiflexion refers to a motion of the head of the talus (see Fig. 12-6) dorsally (or upward) while the body of the talus moves posteriorly in the mortise.
Plantar-flexion is the opposite motion of the head and body of the talus.6/18/2012 [email protected] 59
However, many investigators have concluded from both in vivo and in vitro investigations that: the talus may rotate slightly within the mortise in both the transverse plane around a vertical axis (talar rotation or talar abduction/adduction) and in the frontal plane around an A-P axis (talar tilt or talar inversion/ eversion).[In vivo (Latin for "within the living") is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro ("within the glass", i.e., in a test tube or petri dish) controlled 6/18/2012 [email protected] environment.]
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Such motions result in a moving or instantaneous axis of rotation for the ankle joint. In comparison with motions of dorsiflexion and plantarflexion, these motions are quite small, with a maximum of 7 of medial rotation and 10 of lateral rotation in the transverse plane. Talar tilt (A-P axis) averages 5 or less.6/18/2012 [email protected] 61
Although there is some disagreement regarding the excursion of the joint axis during ankle joint motion, there is consensus among investigators that the primary ankle motion of dorsiflexion/ plantarflexion occurs around an oblique axis that causes the foot to move across all three planes.6/18/2012 [email protected] 62
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Axis
In neutral position of the ankle joint, the joint axis passes approximately through the fibular malleolus and the body of the talus and through or just below the tibial malleolus. The fibular malleolus and its associated fibular facet on the talus are located more distally (Fig. 12-10A) and posteriorly (see Fig. 12-10B) than the tibial malleolus and its associated tibial facet.
The more posterior position of the fibular malleolus is due to the normal torsion or twist that exists in the distal tibia in relation to the tibias proximal plateau.6/18/2012 [email protected] 64
This twisting may be referred to as tibial torsion (or tibiofibular torsion because both the tibia and fibula are involved with the rotation in the transverse plane) and accounts for the toe-out position of the foot in normal standing.
The torsion in the tibia is similar to the torsion found in the shaft of the femur, although normally reversed in direction.6/18/2012 [email protected] 66
Reports of the position of the ankle joint axis in relation to the frontal plane (torsion) are highly variable, ranging from a low of 67 to a high of 327. An average value for this axis angle taken from several studies would be 239.6/18/2012 [email protected] 67
Because of the lower position of the fibular malleolus, the axis of the ankle is inclined down on the lateral side between 104 and 184, which yields an average of 144. Individual variation is high, however, with the magnitudes varying as much as 30 from the average inclination values.6/18/2012 [email protected] 68
Stiehl used a simple hinged model with a level indicator to demonstrate how an axis inclined more distally and more posteriorly on the lateral side will create a motion across three planes (triplanar motion) while still around a single fixed axis.
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He showed that dorsiflexion of the foot around a typically inclined ankle axis will not only bring the foot up but will also simultaneously bring it slightly lateral to the leg and appear to turn the foot longitudinally away from the midline.
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Conversely, plantarflexion around the same single oblique ankle axis will result in the foots going down, moving medial to the leg and appearing to turn the foot longitudinally toward the midline.
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When the foot is weight-bearing, the same relative pattern of motion exists when the tibia and fibular move on the foot. In weight-bearing ankle dorsiflexion, the leg (tibia and fibula) will move toward and medial to the foot, as well as appear to rotate medially in the transverse plane. The opposite occurs during weight-bearing ankle plantarflexion.6/18/2012 [email protected] 72
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End of part -1
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