C l i n i c a l P e r s p e c t i v e F o o t a n d A n k l e B i o m e c h a n i c s A B S T R A C T : Foot and ankle injuries are common in sportsmen and the general population. The impact that the functional anatomy and bio­ mechanics o f the fo o t and ankle complex has on normal gait is reviewed. The abnormal biomechanics associated with overpronation and over­ supination are discussed, as are their consequences. The management principles o f fo o t and ankle injuries are briefly described. KEYWORDS: FO O T AN D A N K LE BIOMECHANICS, OVERPRONATION A N D OVERSUPINATION INTRODUCTION Foot and ankle injuries are extremely com m on, both in sportsm en and in the general population (Rundle, 1995). F ifty -th ree percen t o f all basketball injuries, and 31% o f soccer injuries involve the foot and ankle (Garrick, 1977). A nkle sprains account for the m ost time lost by athletes due to injury (Reid, 1992). The estim ated incidence o f ankle sprains is 1:10 000 people per day in the U nited States (M cCulloch, et al, 1985). The predisposition to injury o f the foot and ankle complex can only be understood by studying the anatomy and biom echanics of this region. THE ANATOMY (See Figure 1.) 1. Talocrural Joint T he ankle is a uniaxial hinge joint. The medial and lateral malleoli (mortice) and the talus, also known as the talocrural joint, have an inherent bony stability. T he position and orientation o f the ligam ents (predom inantly the lateral li­ gam ent complex, the deltoid or medial ligam ent and ligaments o f the syndes­ m osis) further enhance this passive sta­ bility. The muscles crossing the ankle (flexor hallucis brevis; flexor digitorum; gastrocnem ius; soleus; peroneus longus; brevis and tertius; extensor digitorum longus and extensor digitorum brevis) provide active stability. Figure 2.1 show the lateral ligam ent complex consisting o f the anterior talo­ fibular ligam ent (ATL), the calcaneo- fibular ligam ent (CFL) and the posterior talofibular ligament (PTL). Renstrom and Konradsen (1997) include the sub­ talar ligam ents in the lateral ligament FIGURE 1. The joints of the ankle and foot contribute to the combination of movements that occur during gait. (Adapted from "Reid D 1992 Sports injury assessment and rehabilitation. New York: Churchill Livingstone.) M id fo o t ___________I I____________ Forefo o t ____________ I CORRESPONDENCE: L J H unter Physiotherapy D epartm ent University o f the W itwatersrand 7 York Road Parktown 2193 Tel: (O il) 488-3450/2 (w) (011)465-4615 (h) Fax: (011)488-3210 com plex, and B oruta et al (1990), include the lateral talocalcaneal liga­ ment as a fourth com ponent of the com ­ plex, but most authors are in agreement about the ligam ents nam ed above. The ATL is long and thin and m ay be considered a thickening of the anterior joint capsule. Because of its orienta­ tion, its main function is to lim it inver­ sion w hile the foot is plantar flexed (Rasmussen, 1985). The ATL is relaxed HUNTER L J, BSc PHYSIOTHERAPY FORTUNE J, BSc PHYSIOTHERAPY2 P h ysiotherap y Department, U niversity o f the W itw atersrand Physiotherapy Departm ent University o f the W itw atersrand SA Jo u r n a l o f Ph y s io t h e r a p y 2000 V o l 56 No 1 17 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) FIGURE 2.1. The lateral ligament complex consisting of the anterior talofibular ligament, the calcaneofibular ligament and the posterior talofibular ligament. (Adapted from "Reid D 1992 Sports injury assessment and rehabilitation. New York: Churchill Livingstone.) 1 FIGURE 2.2. The medial or deltoid ligament complex consisting of the posteri­ or tibiotalar fibres, tibiocalcaneal fibres, and tibio-navicular fibres. The plantar calcaneo-navicular ligament is depicted. (Adapted from "Reid D 1992 Sports injury assessment and rehabilitation. New York: Churchill Livingstone.) in the neutral position o f the foot. The CFL is relaxed in normal standing and does not have a m ajor role in talotibial jo in t stability. It appears to limit exces­ sive dorsiflexion and acts as a guide for the axis of subtalar jo in t motion (R enstrom et al, 1988). The role o f the P T L is un clear and co n troversial (Rundle 1995, Renstrom and Konradsen, 1997), but it m ay be taut in dorsiflexion (Renstrom and Konradsen, 1997) or in eversion and plantar flexion (Rundle, 1995). Donatelli (1996) claim s the PTL is the prim e stabiliser during plantar flexion. The lateral ligam ent com plex is therefore vulnerable to injury during dorsiflexion, plantar flexion and inver­ sion. Figure 2.2 shows the medial or deltoid ligament. The deltoid ligam ent is strong and therefore m uch less likely to be injured. It lim its eversion o f the ankle. If the deltoid ligam ent is dam aged, an associated fracture o f the lateral m al­ leolus or a tearing o f the tibiofibular syndesm osis must be excluded. The hinge jo in t allows dorsi and plan­ tar flexion with some accessory gliding. D orsi and plantar flexion m ovem ent does not occur in one plane, but three (the triplanar m ovem ent of the ankle). This is due to the asym m etrical shape o f the body o f the talus, and the obliquity o f the ankle jo in t axis (approxim ately 40° anterior o f the frontal plane on the medial side of the ankle) (N orkin and Levangie, 1992). The ‘com ponents’ o f dorsi and plantar flexion will vary, depending on whether the m ovem ent is perform ed in an open chain or a closed chain. In an open chain m ovem ent, i.e. the foot is free and non­ w eight bearing, dorsi-flexion involves a b d u c tio n a n d e v e rs io n , an d p la n ta r fle x io n includes adduction and inver­ sion. However, during a closed chain movem ent, i.e. w eight bearing position, do rsiflex io n inclu d es adduction and inversion, and plantar flexion involves abduction and eversion. Patients with foot and ankle problem s m ust therefore be assessed in weight-bearing and non­ w eight bearing positions e.g. lying and standing (Donatelli, 1996). The m ost stable position o f the ankle is in dorsiflexion as the talus ‘lo ck s’ into the ankle m ortice (the close-pack position). Conversely plantar flexion is the m ost unstable position. 2. Subtalar Joint This is the articulation betw een the cal­ caneus and the talus, i.e. the rearfoot. Supination and pronation occur at the su b talar jo in t, in co m b in atio n w ith accessory movem ents. A bduction and dorsiflexion occur with pronation, and ad d uction and p la n ta r flexion w ith supination. This m ovem ent o f the sub­ talar jo in t alters the rearfoot and forefoot angles (Heil, 1992), and allows the foot to adapt to changes in terrain. W hen the subtalar jo int is in a neutral position, the joints o f the foot, ligam ents and ten­ dons o f the foot are least stressed. 18 SA Jo u r n a l o f P h y s io t h e r a p y 2000 V o l 56 No 1 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) This is the position in which the foot best supports the b o d y ’s weight (Heil, 1992). 3. Midtorsal Joint This jo int complex consists o f the cal­ caneocuboid and talonavicular joints, w hich link the subtalar jo in t with the forefoot. Due to the shape of the arti­ cular surfaces, the movem ents in the m idtarsal jo int occur in com bination, i.e. plantar flexion and adduction occur with supination, and dorsiflexion and ab­ duction occur with pronation (Donatelli, 1996). NORMAL BIOMECHANICS The norm al biom echanics o f the foot and ankle depend on static and dynamic com ponents. The bones, articular sur­ face congruity, ligaments and fascia con­ stitute the static component. The dyna­ mic com ponent depends on muscle work and m ovement o f the tarsal bones. The functions o f the foot and ankle are to provide: i. a flexible base to adapt to uneven surfaces. ii.support for the body’s weight in both static (standing) and dynamic (w alk­ ing) positions. The talocrural, subtalar and midtarsal join ts w ork together. D uring w alking, the gait cycle is divided into the stance (weight bearing) and sw ing phases. Traditionally, the stance phase is further divided into heel strike, foot flat, midstance, heel off and toe off (Norkin and Levangie, 1992). T h e gait laboratory at R ancho Los A m igos M edical Center describes the subunits o f gait by another set of terms. The stance phase is divided into initial contact, loading response, midstance, term inal swing and pre-sw ing. The swing phase is divided into initial swing, m id swing and term inal swing (Norkin and Levangie, 1992; Donatelli, 1996). At initial contact, (See Table 1) the heel strikes the ground on its lateral aspect. The b ody’s weight is transm itted down through the tibia and talus, which is medial to the ground reaction force. This results in adduction of the talus, which initiates and produces pronation o f the foot. The pronation ‘unlocks’ the m idtarsal join t, allow ing the foot to absorb shock and adjust to the terrain. Supination occurs during early mid- stance, bringing the foot to a neutral position at midstance. Supination conti­ nues during the midstance and toe-off (pre-swing) stages. This is essential as supination ‘lock s’ the midtarsal jo int m aking the foot into the rigid lever nec­ essary for effective push-off. During the sw ing-through phase the foot m oves fro m p la n ta r flexion to dorsiflexion and is relaxed. Just before initial contact (heel strike), tibialis anterior contracts to produce dorsiflexion and this results in slight supination o f the foot. At initial contact (heel strike), therefore, the foot is supinated and rigid. As the lateral aspect o f the heel connects with the ground, the talus adducts, initiating pronation once more. D uring gait, the m uscles initiate m ovem ent, stab ilize the bones and decelerate movement. This unloads the ligam ents and joints (Donatelli, 1996) e.g. tibialis anterior contracts maximally im m ediately after heel strike to deceler­ ate the tibia and prevent a posterior shearing force at the talocrural joint, and to control pronation of the foot. Incorrect biom echanics will not only affect the ankle and subtalar joints, but may well result in dysfunction of, and pain in, the other joints o f the lower limb and spine, especially the knee, midtarsal and forefoot joints. ABNORMAL BIOMECHANICS A bnorm al pro n atio n and supination result in hypermobility and hypomobility o f the fo o t respectively (D onatelli, 1996). The overpronated foot can be recog­ nised by an everted calcaneus, medial bulging o f the navicular tubercle, abduc­ tion o f the forefoot relative to the rear- foot and a reduced height o f the medial lon g itu d in al arch (D on atelli, 1996). This should be assessed in standing. A bnorm al p ronation resu lts in a reduced tim e for resupination o f the foot to occur (Paulsen, 1991). The forefoot rem ains unlocked and hyperm obile, which reduces its ability to bear weight, and substantially reduces its effective­ ness as a rigid lever for push-off. If this is the case, soft tissues break down, m uscle functions change and bony rem odeling may occur. These changes may produce a secondary rig id deform ity, w hich mimics the oversupinated foot in its inability to absorb shock and adapt to changes in terrain (D onatelli, 1996). The overpronated foot is associated with overuse injuries. James et al (1978) established that 58% o f patients with overuse injuries overpronated their feet. C hronic in flam m ation, as found in overuse injuries, results in large num ­ bers of fibroblasts in the area causing increased collagen production. This increased collagen reduces jo in t m obi­ lity and soft tissue extensibility. D uring m idstance the foot is pronated and not neutral. This creates a torque in the leg, as the foot is internally ro ta t­ ing as the hip is pushed into external TABLE 1. The phases of gait, comparing the Traditional and Rancho Los Amigos nomenclatures. (Adapted from "Donatelli R 1996 The biomechanics of the foot and ankle. Second Edition. Philadelphia: F A Davis Company" Stance Phase Swing Phase Traditional H eel strike Foot flat M id s ta n c e H eel o ff Toe o ff A c c e le ra tio n M id s w in g D e c e le ra tio n Rancho Los Amigos Initial contact Load ing response M id s ta n c e Term inal sw ing P re­ sw ing Initial sw ing M id s w in g T erm inal sw ing SA Jo u r n a l o f P h y s io t h e r a p y 2000 V o l 56 No 1 19 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) rotation by the sw ing-through action of the opposite leg (Heil, 1992). T he over- pronated foot m ay produce knee sym p­ toms, especially medially. The normal cephalad and external rotation m ove­ ments o f the fibula during weight bearing are also reduced, resulting in dysfunc­ tion o f the superior tibio-fibular joint and pain (Donatelli, 1996). T he oversupinated foot lacks pro­ nation, m aking the foot rigid. This can increase ankle lateral ligam ent stability problem s and pain due to reduced shock absorption e.g. lateral knee pain and stress fractures. The oversupinated foot has an inverted calcaneus, a high medial arch and fore­ foot plantar flexion - again, this needs to be assessed in a w eight-bearing position (Donatelli, 1996). MANAGEMENT PRINCIPLES T h e g eneral p rinciples o f m anaging patients with foot and ankle injuries are to: i) identify and treat the precipitating factors (biom echanics) ii) estim ate the stage o f healing of the injury iii) determ ine the focus o f the initial treatment iv) control the pain and inflam m ation v) initiate an appropriate tensile loading program m e (Chazan, 1998) It is essential to identify the source and contrib u tin g factors o f painful inflam m ation of the ankle and foot to ensure proper diagnosis and treatment (M ooney and M affey-ward, 1995). In the acute inflam m atory stage, the principles of PRICE (protection, rest, ice, com pression and elevation) are used to m inim ise the inflam m atory response and decrease the pain, enhancing the conditions for healing (Donatelli, 1996). The contributing biomechanical factors should be addressed through the wearing o f corrective footw ear or foot orthoses, as well as appropriate m obilisation and strengthening (Heil, 1992). External cushioning, cupping or taping of the heel can im prove shock absorbency and allow early w eight bearing (Schrier, 1995). Increased strength and flexibility of the posterior calf muscles m ay de­ crease w eight-bearing forces, preventing excessive pronation at the subtalar joint. The intrinsic foot muscles should also be strengthened. If there are any signs o f neural tissue involvement, techniques should be used to increase neural m obil­ ity as described by B utler (1991). Patient education and proprioception exercises should be included through all stages of healing. The incidence of re-injury is decreased with the restoration of norm al biom e­ chanics of the foot and ankle. 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