Practitioners surmount pes cavus treatment challenge

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Biomechanics Magazine August 2005

Practitioners surmount pes cavus treatment challenge

http://www.biomech.com/showArticle.jhtml?articleID=167600348

Relatively rarely seen in practice, the high-arched foot may result

from a neurological disorder.

By: Sue Sturgis

When confronting a case of pes cavus, foot specialists can be

forgiven for feeling as though they are entering unfamiliar territory

without a detailed map.

The excessively high-arched foot is rare compared to planus

deformities, according to anecdotal reports from medical experts.

While about 20% to 25% of adults are afflicted with flat feet, the

number of those suffering from excessively high-arched feet is much

smaller, according to Mosca, MD, an orthopedic surgeon at

Seattle's Children's Hospital and Regional Medical Center who has

published an article on the cavus foot1 and is currently writing a

book on the condition.

However, data on comparative incident rates are lacking, as it is

difficult to quantify conditions that aren't clearly bounded.

" No one has defined when an arch is low enough to be called planus or

high enough to be called cavus, " Mosca said.

Moreover, relatively little medical research has been published on

the cavus foot. While the condition's comparative rarity is partly

responsible for its scholarly obscurity, its multifaceted etiology

also shares the blame. Three-quarters of pes cavus cases can be

traced to various and often progressive neuromuscular disorders such

as Charcot-Marie-Tooth disease or amyotrophic lateral sclerosis (Lou

Gehrig's disease).2 The deformity can also have congenital or

traumatic causes.

Mosca said the research is difficult to conduct and to comment on.

" There are so many problems that can create the foot shape, and you

can't just lump them all together, " Mosca said. " But when you

separate them into cavus feet from this and cavus feet from that,

there are so few numbers in each category that it doesn't lend itself

easily to a scientific, prospective, controlled study. "

Furthermore, the terminology used to discuss pes cavus is

inconsistent and can thus be perplexing for the clinician, according

to Green, DPM, of Scripps Mercy Hospital in San Diego.

" The cavus foot is primarily a sagittal-plane deformity, but when you

add in other problems, such as frontal-plane deformities or

neuromuscular disease, it becomes confusing, " he said. " A high

percentage of neuromuscular disease in the cavus foot leads to a

confusion of descriptions. "

Fortunately, the body of knowledge surrounding the cavus foot that's

available to guide clinicians facing the condition is growing. And

technological advances made over the past decade have made treatment

easier for the caregiver and more effective for the patient.

Pinpointing etiology is crucial

Pes cavus is the general term used to describe a high-arched foot,

but the condition typically involves various foot abnormalities,

including rearfoot varus, forefoot equinus, metatarsus adductus, and

digital deformities.3

In the classic article on pes cavus, published in the British Medical

Journal in 1968,2 the authors reviewed 77 cases of pes cavus and

found that 51 showed evidence of neurologic origin. Electromyographic

and nerve conduction studies turned up an additional seven cases with

neuromuscular involvement. Neurological causes of pes cavus include

CMT, which leads to the classic cavus foot shape, as well as spinal

lesions and diseases such as ALS.

Identifying the etiology of the cavus foot is critical in order to

establish whether the problem is progressive, as that will shape the

treatment plan.

Trenton Statler, DPM, a former resident at the Foot and Ankle

Institute of Pittsburgh's Western Pennsylvania Hospital who now

practices in Beaufort, SC, has written about the cavus foot.3 Not all

patients with pes cavus experience symptoms, he noted.

" It can be just another foot variant, like flat foot, " Statler

said. " Unless there are clinical and physical findings of

neurological disorders, treatment is typically tailored towards the

symptoms. "

The childhood symptomatic cavus patients Statler cares for tend to

present with serious neuromuscular disorders such as CMT, while older

patients often seek treatment for callusing, especially under the

first and fifth metatarsals. Chronic ankle pain is another common

cavus complaint, as the rearfoot varus and forefoot valgus associated

with the deformity leave patients vulnerable to lateral ankle trauma

and recurrent sprains.

Because abnormal angulations in the foot can transmit pathomechanical

forces up the leg, pes cavus can also lead to knee, hip, and back

problems, reports , CPO, with Orthotic & Prosthetic

Associates in Chattanooga, TN. also often observes callusing

along the lateral border of the foot and plantar fasciitis or heel

spur syndrome in pes cavus patients.

" That's generally a tension issue, " he said. " The distance their

plantar fascia has to travel is considerably longer than it would be

if their arch was of normal height. That often puts more tension on

an already tight structure, which leads to plantar fascial pain and

insertion or origin disorders that can result in spurs. "

When conducting a clinical examination of the patient with a pes

cavus foot, the goal is to define the deformity and determine which

components are flexible. The evaluation should start with a complete

family history. A neurological consultation will rule out spinal

lesions and cerebellar dysfunction; this examination should include

lower extremity sensory and motor nerve conduction studies. The foot

should be examined both weight-bearing and not, as well as during

normal gait. Because a flexible pes cavus lowers with weight-bearing,

it's harder to recognize than a more rigid cavus condition.

" You generally will get extra contraction of the toes in the swing

phase of gait, so you can often pick it up that way, " Green

said. " Furthermore, you get extensor substitution with significant

contraction of the toes in the swing phase of gait with neurological

disease. "

The lateral block test can help ascertain whether the

deformity is fixed4 and involves the subtalar joint or

the calcaneus. This involves allowing the first ray to hang over the

edge of a one-inch block while the heel and lateral foot remain on

the block. If calcaneal varus corrects, the rearfoot deformity is

reducible; if not, the deformity is considered fixed and typically

involves either the subtalar joint or calcaneus.

X-rays of the weight-bearing foot and ankle are also helpful, as they

reveal elements of pes cavus such as an increased talar-first

metatarsal angle, an increased calcaneal inclination angle, a plantar-

flexed first ray, and digital contractures.

Conservative approaches

Pes cavus treatment aims for a pain-free, mobile, plantigrade foot

with good muscle balance. But choosing the right technique to achieve

this result can be tricky, as no one yet has come up with a hard and

fast system to help practitioners choose among the many approaches

available to address the unique deformities of each patient. Among

the key factors in picking the proper treatment are the patient's

age, the flexibility of the deformity, the magnitude and nature of

the deforming forces, and anticipated foot demands.

If the disorder is non-neurological, nonprogressive, and

asymptomatic, Statler simply monitors the patient over time to ensure

no problems develop. Should pressure spots arise, Statler employs a

combination of shoe modifications, orthoses, and padding to

accommodate the symptoms.

Physical therapy plays a limited role in the treatment of non-

neurological, nonprogressive pes cavus deformity. Flexible cavus feet

typically are asymptomatic and therefore don't require therapy,

Statler noted. And therapy can't correct the rigid cavus foot because

of its fixed structural nature.

When it comes to shoes for cavus patients, Statler recommends models

made on a last that's not too straight and that have solid arch

support and substantial insole cushioning, especially in the

metatarsal zone. He'll often utilize cutouts to make room for callus

formations and pad the insole, so the shoe must be roomy enough to

accommodate this extra cushioning.

Tie shoes generally work better for pes cavus patients since slip-ons

hug the midfoot, which is often the highest point of the cavus foot,

Green said. If patients insist on loafers, they might have them

stretched to accommodate their feet.

A shoe with consistent sole width makes it harder for patients to

find the fulcrum in their heel and roll over, said.

" There are shoes available specifically designed for people who

supinate. They have a harder sole on the lateral portion of the heel

that provides increased resistance against that tendency, " he

said. " And we'll often add a slight flare to the sole. That can be a

lateral wedge, or we can extend the sole out laterally to move the

pivot point away from the axis of the ankle. "

avoids recommending specific brands to patients.

" I like to give them the design criteria so they have some

intellectual knowledge about what we're trying to achieve, " he

said. " I enjoy letting the patient be a part of the process, because

I think we're more successful when we do that. "

Orthotic considerations

In terms of orthoses for the cavus foot, Statler likes semirigid

devices with accommodative cutouts for particular pressure spots as

well as posting in the rearfoot, depending on the degree of calcaneal

inversion.

" You want an orthosis that has some flexibility, " he said. " You don't

want anything real rigid for a cavus foot. "

While also prefers a soft to medium-density orthosis, he

points out that it's not necessary to completely avoid firmer

materials. Because the cavus foot often has a prominent plantar

fascia that a firmer orthosis can irritate, he'll cut a groove in the

device to accommodate the medial edge of the fascia. He'll also cover

the orthosis with a thin layer of soft material to further guard

against irritation.

" The way we treat pes cavus hasn't changed in terms of our goals, but

materials we use have certainly changed, " said. " Today we

probably use 20 different materials in foot orthosis design. Fifteen

years ago, I used two. The availability of dual-density foams and

urethanes has really enhanced what we can offer to the patient. "

Digital scanners have also been a technological godsend, according to

, who swears by his 11-year-old Amfit model.

" You can use the scan to carve the orthosis out of a variety of

materials, and you can also use the scanner to carve out a positive

that's more accurate than hand casts, " he said. " It's improved my

ability to solve problems on the first go-around rather than have to

go through a trial-and-error process. "

Progressive cavus demands surgery

When confronting progressive forms of pes cavus, practitioners should

not use orthoses to put off more invasive procedures, Mosca said.

" If you put on an orthosis to delay the surgery, all you're doing is

adding more procedures to the reconstruction that you'll eventually

do, " he said. " It makes more sense to treat early in order to balance

the muscles before a rigid deformity can develop. "

Mosca sees two basic components to the cavus foot: the misshapenness

and the muscle imbalance that created the misshapenness.

" One has to both correct the shape to make it look like a foot and

then perform tendon transfers to maintain the correction, " he

said. " If you correct the shape and don't transfer tendons, the

deformity will recur. If you just transfer tendons and don't correct

the shape, then you'll have a well-balanced deformity. Because you

want a well-balanced, good foot shape, you need to correct both

concurrently. "

Besides tendon transfers, other surgical procedures used in the cavus

foot include soft-tissue releases, osteotomies, and arthrodesis-but

the latter should be reserved for desperate situations, experts

advise.

" Salvaging joints is my primary focus, " Statler said. " You can always

fuse down the road. "

Because the joints in the cavus foot are out of whack, it's necessary

to align them through soft-tissue procedures such as lengthening

tendons and releasing joint capsules, Mosca said. If the foot still

looks deformed, that means the bones have become misshapen and

require osteotomies.

Fluoroscopy-assisted guide pins are helpful in midfoot osteotomies,

Statler noted.

" Once you have a pin in place, you're allowing the saw blade to pass

through the osseous structures based on that guide, " he said. " You're

not just going through there blind. "

While some have called for correcting the cavus foot with an

osteotomy at the base of the first metatarsal,5 Mosca is skeptical of

that approach.

" If the osteotomy is performed there, it actually creates problems by

bringing the first ray up too far and shifting stress to the second

metatarsal head, " he said.

In fact, the cavus site of deformity is the medial cuneiform just

proximal to the first metatarsal, Mosca noted. When the osteotomy is

performed at that point, the metatarsals come up like a fan and

stress is not transferred to the second metatarsal. It's particularly

important to perform the osteotomy at the cuneiform in children, as a

growth plate sits at the base of the first metatarsal.

Once the foot looks normal, tendon transfers are the next step in the

treatment.

" Know what the muscle imbalance pattern is and then perform a series

of tendon transfers to take from the strong side and transfer to the

weak side, " Mosca said.

He likens the surgeon's role in performing such transfers to a

puppeteer choosing which string to pull.

Even with surgery, however, patients with progressive pes cavus often

develop a drop foot. In those cases, Green recommends a functional

orthosis like a Richie brace, which offers a foot orthosis as well as

ankle stability.

" It's better than the drop foot leg brace in that it does control the

foot as well, so you don't get the irritation over the medial or

lateral malleolus, " Green said.

Finally, keep in mind that even the most successful surgery won't

provide an end-all solution to progressive cavus.

" Always tell patients with cavus deformities due to neuromuscular

disorders that they're never going to have the last operation, " Mosca

advises. " The goal is to perform procedures that leave the most

options available for next time. "

Sue Sturgis is a freelance writer based in Raleigh, NC.

References

1. Mosca VS. The cavus foot. J Pediatr Orthop 2001;21(4):423-424.

2. Brewerton D, Sandifer P, Sweetnam D. " Idiopathic " pes cavus: an

investigation into its etiology. Br Med J 1963;5358:659-661.

3. Statler TK, Tullis BL. Pes cavus. J Podiatr Med Assoc 2005;95

(1):42-52.

4. SS, Chesnut WJ. A simple test for hindfoot flexibility in

the cavovarus foot. Clin Orthop Relat Res 1977;(123):60-62.

5. Watanabe RS. Metatarsal osteotomy for the cavus foot. Clin Orthop

Relat Res 1990;(252):217-230.