Pes Cavus and Pes Planus

Pes Cavus and Pes Planus Analyses and Treatment ABBY HERZOG FRANCO

The arch of the foot serves as an adaptable, supportive base for the entire body. This article discusses how the arch of the foot affects the normal biomechanics of the lower limb. An anatomical overview of the three components of the arch of the foot is presented, identifying the medial longitudinal arch as the arch mainly responsible for related structural problems throughout the lower limb. Deviations in the normal structure of the medial longitudinal arch produce unbalanced, functionally unstable conditions of the foot such as pes cavus or pes planus. Specific evaluation criteria for both pes cavus and pes planus are discussed, in addition to the adverse effects these two disorders have on weight bearing, force dissipation, and normal gait. Compensatory pronation associated with pes planus is one of the most common lower extremity disorders seen currently by physical therapists working in sports medicine, and its causes and related lower limb disorders are discussed. Most of these structural deformities can be corrected through the use of various orthotic devices. Specific guidelines are presented for using both soft and permanent orthoses, which offer the foot increased shock absorption and proper structural alignment.

Key Words: Foot, Orthotic devices, Physical therapy.

A functional relationship exists be-tween the structure of the arch of the foot and the biomechanics of the lower limb. The arch of the foot provides an elastic, springy connection between the forefoot and the hindfoot. This relation-ship ensures that most of the forces in-curred during weight bearing can be dis-sipated before reaching the long bones of the leg and thigh.

The arch of the foot demonstrates two extremes of anatomical structural posi-tionthe high arch characteristic of pes cavus and the flat arch characteristic of pes planus. Although three distinct arches function to support the foot, the medial longitudinal arch (MLA) has been found to be the arch of clinical significance in both of these disorders. Problems and malalignments originat-ing specifically with the MLA ultimately affect the functioning of the muscles and joints of the ankle, knee, hip, and low back, all of which depend on the base of support provided by the MLA.

A strong need exists for physical ther-apists to understand applied anatomy and biomechanics of the arch of the foot

as it relates to common lower limb dis-orders. Muscular imbalances, structural malalignments of joints, compensatory pronation of the foot, and gait abnor-malities often are caused by pes cavus or pes planus. After a comprehensive evaluation, the physical therapist can use various orthotic devices to balance the foot and restore normal function of the lower limb.

ANATOMICAL OVERVIEW The intricate alignment of the bony

structure of the foot, produced by the tarsal and metatarsal bones and their corresponding ligaments, results in the interdependent formation of one trans-verse and two longitudinal arches. These supporting arches are designed to absorb and distribute body weight and to im-prove locomotion by increasing speed and agility during gait. The plantar arches provide both stability and flexi-bility, meeting the different, complex requirements of the foot at different phases of the gait cycle.1-5 The arches must act as a rigid lever for proper mo-bility, but they also must be resilient and flexible for adaptation to different surfaces.

The design of the arches can be under-stood by picturing the foot as a twisted osteoligamentous plate.2 The anterior edge of the plate (formed by the meta-tarsal heads), is horizontal and in full contact with the ground. The posterior edge of the plate (the posterior calca-

neus), is vertical. The resulting twist forms the longitudinal and transverse arches. During weight bearing, the plate will untwist, flattening the arches slightly. As the foot is unloaded of weight, the resilient arches return to their original shape. The actual mecha-nism of twisting and untwisting is ac-complished through motion at the talo-calcaneonavicular, transverse tarsal, and tarsometatarsal joints that link the bones of the plantar arches.2

The transverse arch of the forefoot is located immediately behind the meta-tarsal heads and can be visualized span-ning across the tarsometatarsal joints, its integrity being maintained by the wedge-shaped cuneiforms. The middle cuneiform serves as the keystone of the transverse arch.6 At the level of the metatarsal heads, the curvature of the arch is reduced greatly because the metatarsal heads are in alignment, par-allel to the weight-bearing surface. Also assisting in holding the base of the arch together are the tendons of the peroneus longus muscle, the oblique head of the adductor hallucis muscle, and the flexor hallucis brevis muscle.7

The longitudinal arches, both medial and lateral, are supported by the plantar ligament arising from the calcaneus and extending forward to attach to the meta-tarsals near the heads.8 The longitudinal arch also is supported by the plantar aponeurosis, which is the dense fascia that spans from the calcaneus to the

Ms. Franco is a student in the physical therapy program, Florida International University, Tam-iami Trail, Miami, FL 33199. She was Head Ath-letic Trainer, Barnard College of Columbia Univer-sity, 606 W 120 St, New York, NY 10027, when this study was conducted. Address correspondence to 8181 Boca Rio Dr, Boca Raton, FL 33433 (USA).

This article was submitted March 27, 1986; was with the author for revision three weeks; and was accepted July 23, 1986. Potential Conflict of Inter-est; 4.

688 PHYSICAL THERAPY

PRACTICE

Fig. 1. Supporting structures of the medial longitudinal arch: 1) The tibialis anterior, 2) the tibialis posterior, 3) the spring ligament, 4) the plantar aponeurosis.

proximal phalanx of each toe.4,9 The lateral longitudinal arch is formed by the bony structural relationship between the calcaneus, cuboid, and metatarsals, with the cuboid serving as the keystone of the arch.10 Both the long and short plantar ligaments restrict motion at the calcaneocuboid aspect of the transverse tarsal joint by maintaining the normal twist between the forefoot and hindfoot.

The integrity of the MLA is preserved by the bony structure of the foot, strong ligaments, and active muscles (Fig. 1). The MLA is composed of five bones, with the navicular serving as the key-stone of the arch.6 The spring ligament, or the plantar calcaneonavicular liga-ment, is the main support of the MLA.1 As the spring ligament crosses the trans-verse tarsal joint (the calcaneocuboid and talonavicular joints), it restricts joint motion that contributes to the flat-tening of the arch. During weight bear-ing, the spring ligament offers some elasticity and springiness to the arch.2 Normally, the dorsum of the foot is domed because of the MLA. The arch is more prominent in the nonweight-bearing position than in the weight-bearing position. The MLA is reinforced further by the tibialis anterior and tibi-alis posterior muscles, whose tendons pull the medial border of the foot up-ward.6 The long flexor muscles, whose

Fig. 2. Normal foot. Weight bearing is dis-tributed evenly on all five metatarsal heads.

tendons are attached to the foot behind the medial malleolus and under the MLA, also offer support and act like a sling.7 Evidence exists, however, that the muscles related to the arch are inactive during standing and that the ligaments

alone maintain the arched form of the foot.11 The MLA, which is the arch of clinical significance in both pes cavus and pes planus, will be the arch referred to in the remainder of this article.

NORMAL WEIGHT BEARING AND FORCE DISSIPATION

In normal weight bearing, forces are transmitted through the talus to the me-dial aspect of the foot, specifically to the talonavicular part of the transverse tar-sal joint, causing pronation of the fore-foot. The weight of the body drives the head of the talus downward between the calcaneus and the navicular, and this force is resisted by the spring ligament.7 This downward motion is accompanied by eversion of the calcaneus at the sub-talar joint and slight depression of the navicular.4 In the normal foot, the lat-eral portion of the MLA rests on the ground. This contact, in addition to the absorption of forces at all five metatarsal heads, offers additional support to the foot (Fig. 2).

In the properly aligned foot, the cal-caneus is in a vertical position, perpen-dicular to the horizontal metatarsal heads. Because the metatarsals must re-main flat on the floor for weight bearing, their positional relationship with the cal-caneus and thus the shape of the MLA are controlled by the plantar aponeu-rosis. Hicks found that the plantar apo-neurosis absorbed about 60% of the stress of weight bearing.12,13 As the toes are extended during the push-off phase of gait, the increased tension in the plan-tar aponeurosis raises the MLA by facil-itating supination (Fig. 3). This mecha-

Fig. 3. Windlass effect. Tightening of the plantar aponeurosis on push-off increases the medial longitudinal arch. This increase stabilizes the foot during ambulation as weight is shifted onto the ball of the foot.

Volume 67 / Number 5, May 1987 689

nism is known as the windlass effect.13 The pronation that occurs immediately on weight bearing slightly flattens the MLA, which aids in the absorption of shock.

PES CAVUS In the extremely high-arched foot

characteristic of pes cavus, weight bear-ing is distributed unevenly along the metatarsal heads and along the lateral border of the foot (Fig. 4). This type of disorder causes the foot to be prone to metatarsal head and calcaneal contu-sions resulting from the excessive pres-sure of weight bearing. The foot also is prone to osteophyte formation at the junction of the metatarsal bases and the cuneiforms. This area is quite promi-nent under the skin and quite suscepti-ble to damage.8

To identify pes cavus, the patient should sit at the edge of a tabletop with his foot dangling in a nonweight-bearing position. If the forefoot is lower than the heel and the arch is high but depresses on weight bearing, the patient's condi-tion may be diagnosed as "flexible" pes cavus. If the arch remains high when the patient is in a full weight-bearing posi-tion, the condition is "rigid" pes cavus.14

The foot with flexible pes cavus usu-ally displays a callus under the second metatarsal head. This condition is caused by the arch's inability to dissipate forces and lack of shock absorption. The foot with flexible pes cavus responds well to orthotic devices, which support the MLA, balance the foot, and provide shock absorption.

The foot with rigid pes cavus poses additional problems. Besides callus for-mation under the first, second, and fifth metatarsal heads, these feet have tight, cordlike plantar fascia resulting from the stresses created by the high arch. The abnormal stresses produced by the struc-tural problems of a rigid, high-arched foot also tighten the Achilles tendon and produce claw toes.9

Because of poor shock absorption and a very small weight-bearing area, feet with either flexible or rigid pes cavus are prone to heel pain and stress fractures, in addition to various shock-related pathological conditions that are trans-mitted up the leg to the knees and hips 8,10,14,15 Both types of pes cavus usu_ ally are accompanied by excessive in-version at the subtalar joint and supi-nation of the forefoot at the transverse tarsal joint (Fig. 5).4 Calluses develop under the metatarsal heads when abnor-mal weight bearing must be accommo-

dated. The forces of weight bearing com-monly are shifted to the dropped head of the second metatarsal, causing plan-tar callus formation.16

Treatment for this condition should be directed at providing arch support, structural alignment, and shock absorp-tion through the use of orthotic devices and should include stretching of tight musculature throughout the lower limb. The orthotic device for a high-arched foot usually is made of soft, flexible materials to increase foot shock absorp-tion. These softer, flexible materials often compromise joint control, how-ever, making treatment for this condi-tion more difficult. The physical thera-pist can further help the patient with pes cavus by evaluating the lower limb for muscular imbalances. Tight ankle in-verter and plantar flexor muscles and weak ankle everter muscles often ac-company pes cavus. Stretching the tibialis posterior and the gastrocnemius-soleus complex and strengthening the peroneal muscles will help to balance the foot's supporting structures in an effort to restore the foot to its proper alignment.

PES PLANUS

In pes planus, the head of the talus is displaced medially and plantarward from the navicular. This displacement stretches the spring ligament and the tendon of the tibialis posterior muscle,

Fig. 4. Foot with pes cavus. Weight bearing is on the lateral border of the foot and first, second, and fifth metatarsal heads.

Fig. 5. Supinated foot with pes cavus. Note the inversion at the subtalar joint.

resulting in the loss of the MLA.16 Be-cause of this medial displacement of the talar head, a callus may develop where the prominent talar head presses against the medial counter of the shoe. When viewed from the posterior aspect of the foot, the calcaneus will be everted. The person whose calcaneus is in valgus will have a relatively flat-arched foot because of the untwisting of the interconnecting ligaments of the forefoot and the hind-foot. If the MLA is absent in both seated and standing positions, the patient has "rigid" flatfoot. If the MLA is present while the patient is sitting or is standing up on the toes, but disappears during foot-flat stance, he has "supple" flatfoot, which is correctable with arch sup-ports.16

The flattening of the MLA disrupts the normal process of weight bearing and causes functional changes in the foot. Many people with pes planus dem-onstrate a flat-footed gait with no toe-off,10 often associated with a large plan-tar weight-bearing surface (Fig. 6). Symptoms include a pronated foot, a shortening of the everter muscles of the foot (ie, the peroneal muscles), tender-ness of the plantar fascia, and laxity of the supporting structures of the medial side of the foot (ie, the medial ligaments or deltoid group) and the tibialis poste-rior tendon.17 Over time, this functional


PRACTICE

Fig. 6. Foot with pes planus. Note large weight-bearing surface with main force ab-sorption on first and second metatarsal heads.

deformity will develop into a chronic structural deformity, and abnormal stresses will be transferred to more prox-imal areas, affecting the knees, hips, and low back.

Pes planus is not necessarily sympto-matic. Many cases of fallen arches are painless because the foot adapts by changing the shape of bones and by the stretching of ligaments. The structural changes that accompany a flat-arched foot, however, affect the normal bio-mechanics of the lower extremity. Pro-nation, which is a normal component of gait, becomes exaggerated in the foot with pes planus. The lack of an arch maintains the foot in a flexible, unstable position, hindering normal gait and cre-ating a wide variety of compensatory pronation disorders. An understanding of the components of pronation and its role during gait is necessary before the compensatory pronated foot can be dis-cussed.

PRONATION AND GAIT Pronation is an integral component

of the stance phase of gait. Normal pro-nation is 4 to 8 degrees.15,18 Pronation for a foot with pes planus is between 10 and 12 degrees.15 Pronation of the fore-foot, which causes flattening of the MLA, also flattens the transverse arch by splaying or spreading the metatarsals. The movements of pronation and supi-nation are produced when the foot ro-tates around its long axis, the second

ray. Pronation is a component of a more complex motion, eversion. Eversion of the forefoot is a combination of move-ments in all three planes (ie, pronation, dorsiflexion, and abduction).1,4,5

In the initial phase of gait, the foot contacts the ground in supination. This inversion of the calcaneus at the subtalar joint locks the forefoot and provides the rigid lever to absorb the force of heel-strike. Immediately after heel-strike, the hindfoot pronates to unlock the trans-verse tarsal joint and create a loose-packed position in the forefoot. As the posterior aspect of the calcaneus rolls laterally, the sustentaculum tali of the talus rolls medially, producing the pro-nation.1119 The direct effect of this pro-nation is to create a shortening of the lower limb immediately after heel-strike, while providing a small degree of shock absorption.3 This change allows the foot greater flexibility of movement to adapt to changing ground surfaces. When the foot overpronates during this phase, the tibia also rotates medially, causing the knee to flex earlier than

normal. This flexion puts abnormal stresses on the quadriceps femoris mus-cles, which are contracting eccentrically to control knee flexion.4

In the late stance phase of gait, the foot again must function more as a rigid lever. This action requires an elevated arch and a locked forefoot. The foot inverter muscles, in addition to the sec-ondary actions of the triceps surae and tibialis anterior muscles, cause the cal-caneus to invert at the subtalar joint. This inversion produces supination at the transverse tarsal joint and lateral rotation of the tibia.11 The act of supi-nation causes the osteoligamentous plate of the MLA to twist and tighten, which elevates the arch and locks the foot, providing the rigid lever needed for push-off.

A flat-footed person requires more muscle action than a nonflat-footed per-son to support and propel the weight of his body.2 In pes planus, the hindfoot is in valgus (Fig. 7). This eversion at the subtalar joint creates an untwisted foot with little or no ligamentous support. If, at heel-strike, this foot makes impact in the valgus position, the foot is mobile already and is unprepared to act as a rigid lever to absorb these ground forces. The foot, therefore, must rely on acces-sory muscles for stabilization. This ac-tivity fatigues not only the extrinsic muscles but also the intrinsic muscles of the foot, which are functioning maxi-mally to compensate for the lack of ligamentous support.

COMPENSATORY PRONATION The most common pathomechanical

problem associated with pes planus is compensatory pronation. Overprona-tion and pes planus are key factors in preventing the subtalar joint from lock-ing during the complex biomechanical functioning of the lower extremity. This failure of the subtalar joint to lock cre-ates a hypermobile foot, setting the stage for structural deformities and problems throughout the lower quarter. The phys-ical therapist can use three static obser-vations to detect abnormal pronation: 1) Helbing's sign, the medial bowing of the Achilles tendon secondary to calca-neal valgus; 2) Feiss's line, indicating the position of the navicular in relation to a line drawn between the first meta-tarsophalangeal joint and the medial malleolus; and 3) the amount and place-ment of callus formation, usually thicker under the first and second meta-tarsal heads and the medial, plantar sur-face of the calcaneus.15

Fig, 7. Pronated foot with pes planus. Note the eversion at the subtalar joint and the medial displacement of the talus and navic-ular.


A common cause of overpronation is a limitation of muscular flexibility any-where along the lower limb. A tight triceps surae causes an early heel-off, which does not allow adequate time for resupination.15 Tight hamstring, hip flexor, iliotibial band, and hip medial rotator muscles all produce a toe-out gait. Toeing out prevents the foot from resupinating before toe-off, leaving a flexible, unstable foot.

Compensatory pronation is associ-ated often with other lower extremity disorders. In the patient with a leg-length discrepancy, excessive pronation of the foot generally is a telltale sign of a longer limb.15 This pronation is ac-companied usually by early knee flexion and longer stance time on the longer limb. In runners who train on paved roads, a functionally longer limb is cre-ated unconsciously by the "crowning" of the road. The sloped surface of the road will cause pain on the "downside" leg, the functionally longer limb. On a small track with sharp-banked curves, medial knee pain usually will occur on the "inside" leg. Forces are transmitted up the leg as the downside foot over-pronates in an attempt to make a func-tionally longer limb shorter.

Another common cause of overpron-ation is forefoot varus (Fig. 8). This disorder can be detected by sitting the patient on a treatment table with his foot hanging over the edge of the table-top. With the subtalar joint in a neutral position, the forefoot will hang in an inverted position at rest. This congenital deformity originates as a supinated foot, but gravity pulls the medial aspect of the foot down when making contact with the ground during weight bearing. The foot thus becomes excessively pron-ated because of the overcompensation of bringing the foot to the ground. In addition to the common problems of tight peroneal muscles and stresses up the lower extremity, which can lead to such problems as shin splints, Hughes found that soldiers with a greater than normal forefoot varus are 8.3 times more likely to develop a stress fracture than soldiers with normal forefoot va-rus.20 A valgus deformity causes the first metatarsal to contact the ground before the fifth metatarsal, which forces all loads to the medial aspect of the foot. The first metatarsal head is twice the size and can absorb 2.6 times the force of the second metatarsal head.20 The head and shaft of the second metatarsal of the overpronating foot with pes planus, therefore, commonly develop

callosities and stress fractures, respec-tively.

Overpronation of the forefoot can lead to subsequent malalignments of the entire lower limb. In response to over-pronation, the tibia will rotate medially. In these patients, the hip adductor mus-cles will be tight, and the external rotator muscles will be weak. The knee tends to assume a valgus position when the foot pronates. The distractive forces on the medial side of the knee lead to medial knee pain. The increased valgus also affects the proper tracking mechanism of the patella, predisposing the knee to chondromalacia and other patella track-ing dysfunctions.1017 Unilateral prona-tion, if allowed to progress to more ce-phalic joints, will lead to a scoliosis. Bilateral pronation will increase the lor-dosis of the lumbar spine.21 Decreasing pronation appears to increase the stabil-ity of the extensor mechanism of the knee and decrease runners' knee symp-toms.22

Treatment for the overpronated foot with pes planus should revolve around reducing the stresses that caused the problem. Long-distance runners with foot, knee, or hip pain secondary to pes planus should reduce their mileage, or perhaps even temporarily stop running, to allow the tissues to heal. A muscle strengthening program to strengthen the anterior and posterior tibialis and intrin-sic foot muscles might increase the mus-cular support of the arch, forcing mus-cles to absorb most of the load. Other

treatments include arch taping or sup-ports, ultrasound to heal damaged tis-sues, stretching of tight muscle groups, and orthotic devices. An understanding of the principles behind the use of or-thotic devices will enable the physical therapist to correct both pes cavus- and pes planus-related problems by realign-ing the weight-bearing surfaces of the foot.

ORTHOTIC DEVICES After a comprehensive lower extrem-

ity evaluation applying their back-ground knowledge of the anatomy and kinesiology of normal foot function, physical therapists should be able to construct foot orthoses to balance the body's base of support. By following several simple principles and using read-ily available, inexpensive materials, nor-mal foot function can be restored in minutes.

An orthosis is a soft, semiflexible or rigid, device whose purpose is to balance the foot in the neutral position during the gait cycle. Soft, temporary supports can be made by adding felt and other soft materials to the insoles of the shoes. These materials, which will adapt to the contours of the foot, help correct prob-lems such as abnormal pronation and supination, offer metatarsal and arch support, and provide better shock ab-sorption. The main function of an or-thotic device is to provide a combina-tion of neuromuscular reeducation and a change in body mechanics in an at-

Fig. 8. A. Normal relationship between the hindfoot and forefoot. Note that the calcaneus and metatarsal heads are perpendicular. B. Forefoot varus. The forefoot rests in an inverted position relative to the subtalar joint, which is in a neutral position. (Adapted from Wallace.15)


PRACTICE

Fig. 9. Structural tripod of the foot: the calcaneus and the first and fifth metatarsal heads.

tempt to readjust the foot into a more ideal weight-bearing position. Arch sup-ports support the arch of the foot; how-ever, they do not balance or offer me-chanical control to the foot.

When making orthotic devices for a patient, several principles should be kept in mind. Most important, undercorrec-tion is the preferred treatment protocol. Maximal foot control is unnecessary, and a balancing effect of the foot is best. Visualize the foot as a structural tripod, with the heel and the first and fifth metatarsals as the bases of support (Fig. 9). The purpose of the orthotic device is to fill in the space between the balanced foot and the ground. Imagine bringing the ground up to the foot. When cor-recting an overpronating foot, remem-ber that the foot has a natural tendency to pronate to some degree, usually 4 to 8 degrees.15,18 An orthotic device should not block all pronation. In addition, an entire lower quarter examination must be performed involving an assessment of muscle strength and flexibility and proper joint function.

An orthotic device consists of two basic parts: 1) the base, the material you start with, and 2) the post, or the extra material that is added to the base to

"bring the ground up to the foot." In forefoot varus, the medial aspect of the foot is posted. Most compensatory pro-nation problems can be corrected by balancing in this manner.23 In the pa-tient with anteromedial knee pain caused by excessive pronation, orthotic devices balance the heel at contact, sup-port the arch at mid-stance, and allow eversion at the subtalar joint just before push-off.24 For pes cavus, a 0.25-in* felt heel lift and a lateral 0.12-in forefoot extension between the lateral half of the hindfoot and the fourth and fifth meta-tarsal heads have been found to be help-ful.22

Soft, temporary supports wear down quickly, and readjustments must be made as needed. A wide variety of tem-porary orthotic devices can be made on the spot with minimal supplies and time.15,25,26 When making temporary or-thotic devices for a patient, the physical therapist might want to use athletic tape either to tape the posting materials into the shoes or to bind the patient's feet into the desired position. When the cor-rect temporary support is given and foot function has improved substantially, a

permanent orthotic device should be custom made.

Permanent orthotic devices are made from a positive model cast of the foot. The two methods most often used are the foam box impression and a plaster-of-Paris slipper cast impression, both taken with the subtalar joint held in a neutral position. The neutral position of the foot is maintained when the long axis of the lower limb and the vertical axis of the calcaneus are parallel. Ther-moplastic, or heat pliable, orthotic ma-terials are molded onto the positive models to form the base. Postings and more durable materials then are added to complete the correction.

In unidirectional sports, such as run-ning, an orthosis can help the foot attain a neutral position at the middle of mid-stance. Rigid orthotic devices, made from a hard plastic material, are pre-ferred by runners and by patients for use during walking and normal daily activ-ities. In sports in which pivoting is in-volved or multidirectional forces are placed on the foot, the orthosis must provide arch control while allowing eversion at the subtalar joint to offer more forefoot flexibility.22 Semiflexible orthotics, made of leather and more pli-able materials, are preferred by these athletes.

SUMMARY

The arches of the foot play an integral role in determining the proper mechan-ics of the entire lower limb. Both pes cavus and pes planus demonstrate typi-cal patterns of structural deformity. Through an understanding of lower limb biomechanics, the physical thera-pist can evaluate and recognize struc-tural imbalances and other disorders that originate with the arch of the foot. When detected, various related, symp-tomatic pathological conditions may be treated and relieved by balancing the foot through the use of orthotic devices. * 1 in = 2.54 cm.


Documents

Pes Cavus and Pes Planus