Cavus foot diagnosis determines treatment
In our center, almost twice the number of painful feet had a cavovarus posture than had a flat foot.
By Arthur Manoli II, MD, and Brian Graham, CPed
Since the introduction of the simple diagnostic test, the "too-many-toes-sign" described by the late Ken A. Johnson, MD, in the early 1980s, the foot and ankle practitioner is now much more easily able to diagnose the pathologic condition of posterior tibial tendon insufficiency (Figure 1).1 This has resulted in a tremendous interest in the acquired adult flat foot, and considerable subsequent research into the etiology and treatment of this common disorder.2
Much less is known of the other common-"opposite"-pathologic disorder, the subtle cavus foot (SCF). In this disorder the foot assumes a posture of an inward tipping of the heel (heel supination or varus), and a related forefoot pronation (forefoot valgus). The first metatarsal is plantar-flexed and the arch is excessively high (cavus).
In the foot clinic, an increased awareness of the many pathologic ramifications associated with this disorder can lead to more accurate diagnosis and treatment. A simple survey in our center showed that, surprisingly, almost twice the number of painful feet had a cavovarus posture than had a flat foot, even though we are a major referral center for the treatment of posterior tibial tendon insufficiency.3
In normal human locomotion, the gait cycle begins at heel strike when the normally pronated heel everts into additional pronation through the subtalar joint, thus absorbing most of the energy of the strike. As the foot comes down to the foot-flat position, weight is transferred along the supple lateral border of the foot, eventually reaching the forefoot, where the metatarsal heads/hallux sesamoids distribute the weight equally.
With the cavovarus foot, the heel strikes the ground in a varus position, and hindfoot eversion is limited, diminishing the shock-absorbing capacity of the subtalar joint. In the subsequent foot-flat position, the lateral border is less supple than normal because of the excessive cavus shape of the midfoot. As weight is transferred to the forefoot, the plantar- flexed first metatarsal strikes the ground first, tipping the forefoot and the entire foot inward. Large calluses may develop under the first and fifth metatarsal heads. The ankle feels unstable and weak. It is the combination of the lack of shock absorption and the inward tipping of the foot that leads to the numerous clinical maladies that are frequently seen.
The subtle cavovarus foot is usually idiopathic, with a strong familial, genetic predisposition. The vast majority of patients that we see with a cavus foot have this mild type of abnormality, rather than one of the more extreme deformities seen with neurological or other disorders.4 Often they have seen numerous other practitioners who have been unable to diagnose the condition because of the subtle signs.
More obvious but less common causes of cavus feet include trauma (especially old fractures of the talus or calcaneus, or Lisfranc joint fractures/dislocations), residual effects of congenital clubfoot, or rheumatoid arthritis. Many neurological disorders (Charcot-Marie-Tooth disease, polio, certain central and peripheral neuropathies, cerebral palsy), and spinal cord neoplasms cause cavus feet. Contractures after leg or foot compartment syndromes give rise to rigid cavus feet. A cavus foot may also be caused by a tarsal coalition. Either a talocalcaneal, calcaneonavicular, or talonavicular bar may be present.5,6
Spectrum of Severity
The cavus foot with an associated tight triceps surae complex runs across a spectrum of severity. The mild type has gastroc-nemius muscle tightness, and a plantar-flexed first ray that are dynamically produced by relative peroneus longus muscle "overdrive." This is diagnosed by having the patient plantar flex the forefoot against the examiner's thumbs, one thumb under the first metatarsal head and the other placed transversely under the lesser heads.7 With peroneal longus overdrive, there is considerably more force and plantar-flexion moment under the first metatarsal head than under the lateral heads.
As ankle equinus increases in severity or becomes more fixed, the peroneus longus muscle actually becomes stronger, as the action of its antagonist muscle, the tibialis anterior, becomes relatively weaker.8 Progressive equinus results in the tibialis anterior's line of pull becoming more parallel to the long axis of the first metatarsal, diminishing the dorsiflexion moment of the muscle. Conversely, the direction of pull of the peroneus longus muscle becomes more perpendicular to the first metatarsal, increasing the plantar-flexion moment. This imbalance eventually results in the first metatarsal becoming fixed in plantar flexion, progressively driving the heel into varus and leaving the foot less stable.9
As the heel is consistently tipped into varus, it tends to become fixed over time. Subtalar motion becomes limited, and hindfoot eversion, external rotation, and dorsiflexion are blocked. The shock-absorbing capabilities of the subtalar joint are lost, and the extremity becomes vulnerable to repeated stress injuries. Besides the forefoot-driven hindfoot-varus spectrum, occasionally a cavus foot may develop from initial hindfoot stiffness. Trauma (old fractures of the talus and calcaneus), old leg or foot compartment syndromes, tarsal coalitions, old clubfeet, and rheumatoid arthritis begin with the hindfoot stiff in varus. Initially, the forefoot is tipped into a supinated position (forefoot varus), but with time, the first metatarsal and the medial forefoot drop downward to meet the ground. The forefoot then becomes fixed in a pronated position, relative to the hindfoot (forefoot valgus). This produces a stiff cavovarus foot. As with forefoot-driven pathology, there is no correction of the heel varus with the Coleman block examination.
The person with cavovarus foot posture tends to walk on the outer border of the foot. The disorder results in recurrent inversion sprains of the ankle and subtalar joint (often necessitating surgical reconstruction), the common Jones-type stress fracture of the fifth metatarsal, and the less common stress fractures of the other lesser metatarsals. Peroneal tendon pathologies include recurrent dislocation or subluxation, tendinitis, splitting, and os peroneum syndrome with either an ossified or nonossified os becoming fragmented and developing pain. Overload callus under the base or head of the fifth metatarsal, metatarsalgia, and hallux sesamoiditis may also result.
Excessive external rotation of the talus and tibia may result in varus strain at the knee joint, increased lateral collateral knee ligament strain, and iliotibial band friction syndrome.10-12 Medial compartmental knee joint arthritis may develop in long-standing cases.
As the SCF is frequently associated with a tight Achilles tendon and tight plantar fascia in the foot, a painful plantar fasciitis may develop.10 If varus ankle arthritis develops, ankle arthrodesis (fusion) or total ankle arthroplasty (replacement) may be necessary. These stiff feet, without the usual shock-absorbing mechanisms, may also produce tibial/fibular stress fractures, leg or foot exertional compartment syndromes, shin splints, and other stress-related disorders of the ankle, knee, hip, and spine.
In 1993 Manoli, Smith, and Hansen described the "peek-a-boo" heel in the equinocavovarus foot following deep posterior leg compartment syndrome.13 The standing patient is viewed from the front. In a normal foot, with anatomic heel valgus, the heel is not visible, being hidden by the posterior foot. Patients with heel varus have a visible portion of the heel pad "peeking out" from the medial border of the foot (Figure 2). Commonly, the patient also has an associated mild bean-shaped foot with a subtle metatarsus adductus and when asked to face the foot forward, they cue on the forefoot and externally rotate the entire lower extremity through the hip to face the foot forward. The patella faces more laterally, and the foot is viewed in this externally rotated position. The "peek-a-boo" heel pad is even more visible .
Looking for this sign in all patients for the past few years we have been able to identify a number of cases of SCF when the diagnosis was not obvious using the usual view of the patient from the rear.14 We feel the "peek-a-boo" heel sign is much more sensitive than previous methods of determining heel varus and just as useful in the evaluation of the problem foot as the "too-many-toes" sign.
Once a "peek-a-boo" heel is identified, it is compared to the opposite side, and different severities are noted. Arch height is estimated. The standing patient is then viewed from the rear, and the diagnosis of heel varus is confirmed. All patients with a heel varus in our center are then studied using the Coleman block test.15 A 1-inch block of wood (or a thick book) is used. The patient is asked to stand on the block, hanging the first metatarsal head off the medial edge of the block. If the heel varus improves and the heel corrects by tipping into valgus, then the subtalar joint is supple and the heel varus is caused by a plantar-flexed first metatarsal (Figures 3A-3B). This may be called "forefoot-driven heel varus" and is a result of the tripod effect of the first and fifth metatarsal heads' relative positions affecting the heel. No correction using the block indicates a rigid heel varus, which usually also has a rigid plantar-flexed first metatarsal.
The triceps surae is then checked for tightness as this usually accompanies the foot deformity. Dorsiflexion of the ankle is checked with the patient seated on the examination table and the knee extended. The ankle should dorsiflex above neutral passively with the foot in neutral inversion-eversion. Examination in eversion allows the foot to dorsiflex through the subtalar joint, giving a false impression that the Achilles tendon complex is not tight.
Lack of ankle dorsiflexion indicates triceps tightness. Because the gastrocnemius muscle loosens with knee flexion, if the ankle can be brought above neutral as the knee is flexed, isolated gastrocnemius muscle tightness is diagnosed. This maneuver has implications for surgical treatment, if necessary, as the gastrocnemius may be lengthened alone, preserving the soleus strength.
Subtalar joint motion can be rechecked with the patient sitting or prone,16 and correlated with the block test in terms of stiffness, plantar flexion of the first metatarsal relative to the other metatarsal heads, and arch height.
In our center, routine radiographic examination consists of standing anteroposterior views of both ankles (same cassette), both feet (same cassette), and lateral views of each foot and ankle together on the same cassette.17
With the cavovarus foot some abnormalities are common. In the lateral radiograph the arch is high, with a distance seen between the bottom of the medial cuneiform and the bottom of the fifth metatarsal.17,18 Meary's line, which in the normal foot aligns the lateral axis of the talus, the medial tarsal bones, and the first metatarsal, shows that the first metatarsal is plantar-flexed. The fibula may appear to be posteriorly placed, relative to the tibia, as the axis of ankle motion is externally rotated; this is the "sagittal breech" as described by Lloyd-Roberts.19 The calcaneus may be dorsiflexed with an increased pitch.
In the standing anteroposterior radiographs of the feet, one can see the hindfoot supination as a diminution of the normal talocalcaneal angle, with the long axis of both bones nearly parallel to each other. The metatarsals show overlap as the hindfoot supination produces a more oblique pattern in more distal bones. A metatarsal adductus may be seen as well.
The standing anteroposterior views of the ankles, taken together, allow for comparison of the height of the feet, as measured from the floor to the top of the talar dome. Asymmetry may be seen if there is a unilateral deformity, with the cavus foot being taller. This view will also demonstrate the externally rotated ankle mortise and talus.
Special views and additional studies may be needed to examine the foot further. An oblique view of the foot helps to evaluate the calcaneonavicular area, in search of a coalition or to evaluate a Jones-type stress fracture of the fifth metatarsal. Stress radiographs of the ankle and subtalar joint evaluate these areas for chronic instability.
A CT scan may be needed if the practitioner suspects a talocalcaneal coalition or any other abnormality of the subtalar joint, as in cases of old trauma, or rheumatoid arthritis. Our center uses 3-mm slices: in the semicoronal plane, perpendicular to the posterior facet of the subtalar joint; and in the axial plane, parallel to the bottom of the foot.
Bone scanning is useful to find occult stress fractures. It can also be used as a screening test to find other painful arthritic conditions, such as a tarsometatarsal arthritis that may develop in a high arch.
After a subtle cavus foot is diagnosed, an attempt is made to isolate the specific clinical problem causing the patient's complaints. Treatment of the foot deformity in combination with treatment of the problem may be necessary. If the foot deformity ignored, recurrence is likely. The high failure rate of lateral ligament reconstructions20 for instability in the cavovarus foot is an example of this principle.
Most of the patients visiting our center have been seen and treated elsewhere before. The vast majority are surprised to hear that they have a varus heel and supinated forefoot. The athletes have almost all been told their feet "pronate." Many come in with hard plastic or fiberglass arch supports, contoured to the bottom of the high arch, with a small heel applied to stabilize the insert in the shoe. These rigid, conforming orthoses actually make the problems of foot stiffness and reduced shock-absorption worse. We have seen a number of stress-related metatarsal fractures from their use.
The many catalogues for over-the-counter orthoses also illustrate many different "arch supports," designed to position materials in the naviculocuneiform area to push up on the arch. We are unaware of over-the-counter devices designed to control the cavovarus foot.
For the treatment of varus knee arthritis, many practitioners have advocated the use of lateral heel wedges.21-24 While the wedges appear to bring knee-pain relief to many patients, attempts to tip a heel into valgus when there is a fixed plantar-flexed first ray forces the medial ray towards the ground. The resulting medial pain may be severe and cessation of treatment may be necessary.
We have also found that lateral shoe wedging to unload the medial knee compartment is sometimes prescribed without considering whether the patient has a hypermobile or pronated foot. While this may reduce knee symptoms, it can induce maladies such as plantar fasciitis and posterior tibial tendon insufficiency in the pronated foot.
Footwear. Selecting the proper footwear is an important and often overlooked aspect of treating the cavus foot. Uppers should be made of a soft, flexible material with long, wide lace openings to accommodate the prominent instep and forefoot. The heel should be flared and a little higher than the forefoot. This supports the hindfoot equinus and inversion instability often found in the cavus foot. The forefoot should have extra depth and an oblique toebox to reduce contact with contracted toes. Outsoles should be more cushioned than rigid, avoiding a medial post that is flared or of a higher durometer. It is also advisable to avoid an extended steel shank when dealing with the cavus foot. Athletic shoes provide the best combination of support and cushion. If social or business constraints dictate that the patient wear a dress shoe, lace-ups are preferred over loafers and a crepe sole over leather.
Orthoses. In our experience it is a far too common occurrence to see a cavus foot patient who already has one or more pairs of orthoses. Many of these devices are fabricated with materials that are too rigid and have an excessively high medial arch support, based on the theory that a high-arched foot needs extra medial arch support, when in fact it needs less.
Almost all custom or prefabricated orthoses that we have seen are made either to correct the pronated flat foot or to support the cavus foot arch. Even in the rare instances where the forefoot has been correctly fashioned with the lateral forefoot post described below, the insert is still made to fit snugly against the under-surface of the medial foot, negating any possible hindfoot pronation the posting might allow. We question how the cavus foot can be treated with short, 3/4-length orthoses without any forefoot extension.
Cavus foot orthosis (CFO). After years of treating the cavus foot with custom orthoses, we have enjoyed a great deal of success by combining several unique design features. However, widespread use of custom orthoses is limited by practitioners' experience, cost, and reimbursement issues.
To treat the cavus foot on a mass scale consistently and cost-effectively, we developed the CFO. This prefabricated orthosis (patent pending), incorporates many of the principles proposed by Bordelon for the treatment of the cavus foot in children.7,25
The design features of the CFO include an elevated heel to cushion and accommodate the excessive heel strike force and tight gastrocnemius muscle found in the cavus foot. An intrinsic lateral heel wedge to induce eversion and redistribute loading to a larger area of the foot may be used. The medial arch height is actually reduced with a recess under the first metatarsal head to accommodate the plantar-flexed first ray and allow some degree of hindfoot pronation, provided it is supple. A forefoot wedge, beginning just lateral to the first metatarsal recess, extends to the lateral border of the device to accommodate the forefoot valgus.
The CFO is made of ethylvinylacetate and can be easily modified by spot heating, additional extrinsic posting, or grinding. Furthermore, the CFO is sized by arch length only. This will eliminate improper size selection by people in whom there is a discrepancy between arch length and heel-to-toe measurement.
Preliminary data indicate that approximately three of four patients experience improved stability and/or pain relief with the use of the CFO. Many of these patients have had numerous other sets of rigid orthoses with either a too-high medial arch, and/or a too-short orthosis that failed to control the forefoot position.
Failure of nonoperative therapy may be an indication for surgical correction. In general, we try a combination of stretching exercises and orthoses for a period of two to three months. If there is no improvement or a worsening of the condition, then surgery may be considered. The specific pathologic problem is addressed, but if the cavovarus foot is a contributing factor, then correcting it must also be considered.
An extremity with a tight gastrocnemius muscle may need a gastrocnemius slide procedure. We prefer a Vulpius lengthening or a medial approach variation using either a single incision through the gastrocnemius tendon or a pie-crusting of the tendon.26 This latter technique allows for a controlled lengthening, and avoids some of the denting of the posterior calf seen with other techniques.
For peroneal overdrive, a peroneus longus-to-brevis transfer is performed just proximal to the peroneal tubercle, allowing the tendon to gap approximately 1.5 cm. The distal peroneus longus tendon is sewn to the brevis tendon to avoid the creation of a dorsal bunion. Lengthening the gastrocnemius alone, without the peroneal transfer, may actually make the overdrive worse, as the peroneus longus may recruit the weakened gastrocnemius muscle to plantar flex the ankle.
We prefer osteotomies to fusions whenever possible. Fixed first metatarsal plantar flexion is treated with a V-type osteotomy of the bone, just distal to the tarsometatarsal joint.9 It is fixed with a 3.5-mm screw, notching the dorsal cortex to avoid splitting.27 Severe deformities may need osteotomies of the second and third metatarsals as well. We have even performed V-type osteotomies of the midtarsal bones (cuneiforms and cuboid), in addition to the metatarsal osteotomies in very severe cases. These osteotomies are performed in patients who have a supple subtalar joint that corrects with the Coleman block test.
If the hindfoot is stiff and does not correct when standing on the block, a lateralizing heel osteotomy is frequently indicated. We perform this at the midportion of the calcaneal tuberosity through an oblique incision, perpendicular to the axis of the tuberosity. The heel is shifted laterally, from 0.5 to 1 cm and fixed with two 6.5-mm screws. Although some have advocated adding a closing wedge osteotomy to the lateral shift, we know of three instances where the medial nerves were stretched with this technique resulting in a painful tarsal tunnel syndrome or regional pain syndrome. Therefore, we now recommend only the shift.
If additional heel lateralizing is needed, this can be accomplished by approaching through a different level, approximately 1 cm from the first one, at a later date. This results in a curving type of calcaneus, with excellent function. This heel osteotomy is particularly useful with recurrent sprains of the ankle as a result of heel varus. It may be performed with either a supple or a stiff sub-talar joint.
In cases of significant deformity and stiffness, occasionally a triple arthrodesis is indicated. The talocalcaneal, talonavicular, and calcaneocuboid joints are denuded of their articular cartilage, and fixed with 6.5-mm lag screws in the position of mild heel valgus, attempting to supinate the forefoot as much as possible through the Chopart's joints.28 Klaue has even performed a medializing-lengthening osteotomy through the talar neck to reposition the foot in severe deformities, with both supple and stiff subtalar joints.29
If the deformity is long-standing, the first ray will be plantar-flexed, and reducing the foot into the position of mild heel valgus with a triple arthrodesis will result in even more plantar flexion there. If this is not corrected with a dorsiflexion osteotomy, the ankle will tip into varus postoperatively. As the hindfoot is already stiff, there is little downside to this combined repositioning procedure.
It is important to recognize the effects that a surgical procedure will have on other parts of the kinetic chain, as severe problems may result from ill-advised operations, particularly if the subtalar joint is stiff and cannot adapt. We have seen a relatively simple first metatarsal dorsiflexion osteotomy done for sesamoiditis in a patient with a genu varum, stiff subtalar joint, and a tight gastrocnemius muscle that resulted in severe ankle and knee pain as the patient tried to rotate his forefoot to touch the ground. Eventually, the osteotomy had to be "undone."
Secondary problems associated with the cavovarus foot often need to be addressed surgically as well. Recurrent ankle or subtalar joint sprains can be repaired with a tightening of the lateral ligaments, with or without augmentation. Peroneal tendon pathology may require suturing a split brevis or longus tendon. Reefing of the superior retinaculum is usually done with this or with recurrent tendon dislocation. Os peroneum syndrome may require removing a fractured os, suturing the peroneus longus tendon, or a local tendon transfer or tenodesis.
A Jones fracture may require screw fixation with or without a bone graft to ensure healing. Sesamoid injuries occasionally necessitate removal of one of the bones. Most other metatarsal stress fractures are treated nonoperatively.
Progressive varus ankle arthritis may require either tibiofibular or heel osteotomies, or an ankle fusion for pain relief.30 The varus ankle is starting to be recognized as a difficult reconstructive situation for total ankle arthroplasties. The cases that are minimally constrained may tip into excessive varus postoperatively if a cavovarus foot deformity cannot be fully corrected.31
Arthur Manoli, II, MD, is clinical and fellowship director of the Michigan International Foot & Ankle Center in Pontiac. Brian Graham, CPed, is director of the Performance Zone in Auburn Hills, MI.
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