A New Device for the Treatment of Metarsus Adductus

Andrew Chong, M.S., F.M.C.S.(c), F.A.C.S.

Abstract

While the usual treatment of moderate to severe metatarsus adductus has been serial castings, a new device has been developed which may be used as an alternative to castings. The ready-made polypropylene orthosis embodies the corrective features of a cast, and its clinical efficacy was confirmed in a prospective study of the children with moderate to severe deformities between the ages of two and eight months. All 116 children obtained complete correction after two to 12 weeks of orthotic wear. The advantages of orthotic treatment over casting include safety, convenience and dramatic savings in cost and time.

Introduction

Metatarsus adductus is a common foot deformity at birth, characterized by adduction of the forefoot in relation to the hindfoot at the tarso-metatarsal joints. There may be some varus of the forefoot associated with the adduction, but the hindfoot or the heel is usually in the neutral position.¹ In most infants, this deformity is mainly postural at birth, and resolves spontaneously in the first two months of life.

In some infants, however, the deformity persists even after two months of age, and becomes increasingly structural and fixed. While some of these instances might still correct spontaneously in the first year of life, treatment becomes increasingly difficult with each passing month. Bleck has demonstrated that if the deformity is not treated before the age of nine months, the chances for complete correction are significantly lower.² The consensus of opinion of orthopedic surgeons at this time is to start active treatment at the age of two to three months.^3-9

Bleck has classified metatarsus adductus into three grades of severity depending on where the heel bisector falls between the toes:

Normal - heel bisector crosses between second and third toes.

Mild - heel bisector passes through third toe.

Moderate - heel bisector passes between third and fourth toes.

Severe - heel bisector passes between fourth and fifth toes.

He also further distinguished between those that are fully flexible (if one can passively overcorrect the deformity), partially flexible (if one can passively correct the foot to the neutral position only), and rigid (where no passive correction is obtainable). In the less flexible forms, a skin crease is often present.

It is generally thought that the mild and fully flexible forms of metatarsus adductus correct spontaneously with time, and no active treatment is required. The moderate and severe forms, which are only partially flexible, require active treatment, especially if associated with a skin crease.

There is general agreement among orthopedic surgeons that in a child two months of age or older, where the deformity is moderate or severe and partially flexible, casting is indicated^10-16 Casting is usually for a period of six to 12 weeks, with weekly or bi-weekly cast changes to accommodate foot growth. Once complete correction has been obtained, the child is put in corrective outflare shoes for two to three months to maintain the correction and prevent recurrence.

Although the results of cast treatment are good, there are distinct disadvantages:

Repeated casting by an orthopedic surgeon trained in casting techniques is required; repeated visits for cast changes incur considerable expenditure of time to both physician and family.
There are possible cast complications. The casting technique is a very exacting procedure. While the cast has to be corrective, any undue pressure can cause skin breakdown. If the cast is too tight, circulatory problems may arise with serious consequences.
The child is too young to complain in any way except cry if the cast is causing any problems. Parents have no indication of trouble except the condition of the toes, since the whole foot is covered by the cast. As a result, skin problems may not be noticed till the next cast change.
Emotional trauma to both infant and family.

Alternatives to casting have been sought over the years, and they basically fall into two groups: shoes (or boots) and orthoses (or splints). In spite of several introductions over the years these alternatives have not been utilized to any significant degree, and casting remains today the treatment of choice. The reason is that these alternatives lack the features that are necessary to correct the deformity.

Shoes and boots have been ineffective in obtaining correction because the flexible material of which they are made does not hold the foot securely enough to effect correction. At the present time shoes are used mainly as a holding device after correction has been obtained with casts.^17-19

Orthoses that have been introduced so far do not hold the heel and the medial portion of the foot securely enough to allow for successful correction of the deformity. They are rarely used for the correction of metatarsus adductus; and if used at all, they serve primarily to maintain the correction that had been previously obtained with casting.^20,21

The Orthosis

The new device (Figure 1 and Figure 2 ) which the author developed and tested in the last three years is an orthosis made of thermo plastic material (polypropylene). It is unique in that it embodies the corrective features of a cast without its disadvantages. It is molded to conform generally to the inner border of the foot in the over-corrected position (Figure 5) and makes use of the following principle of three-point fixation to correct the deformity:

First point of fixation - the heel or hindfoot is securely held by the heel portion of the orthosis to prevent the hindfoot from going into valgus when the corrective force is applied.
Second point of fixation - the distal part of the first metatarsal and great toe are securely held by the foot portion of the orthosis.
Third point of fixation (between the 1st and 2nd points) - provides the corrective force on the lateral border of the foot against the convexity of the deformity by use of a Velcro strap. The amount of correction can be determined and graduated, if necessary, by adjusting the tightness of the strap. In this way, the patient is provided with a relatively inexpensive ready-made device, but customized correction.

When first conceived, the orthosis was made in several different sizes to accommodate size differences in the feet. Subsequent experience indicated that within the age range of the children studied, this was not necessary. By trial and error, one particular size was found that would accommodate most feet between the ages of two to eight months. In the younger infant, the fit may be loose, but as long as the medial border of the heel (first point of fixation) and the great toe second point of fixation) were securely held against the device, the foot strap could be applied effectively against the apex of the deformity. In the older infant, the orthosis might be snug, but as long as the foot including the great toe was properly seated in the brace, it would work. Occasionally, there would be the "hard-to-fit" foot, and slight adjustment to the device might be needed. This could be done with a heat gun to open up the orthosis (Figure 3) or a hand trimmer to remove the edge of the orthosis in the appropriate areas (Figure 4) to allow for more proper fit and effective correction. Needless to say, even within the age range under discussion, there will be occasion when a different size device would be required.

It would appear that if such an orthosis works as well as casting, it would be preferable to castings. The advantages are obvious:

Ease of application and high acceptability. Any interested physician could learn the technique in a matter of minutes, and in turn may teach and supervise the parent in the use of the device.
Avoidance of cast complications, since the orthosis is removed twice a day for cleaning. Any serious skin breakdown and circulatory problems are thus avoided.
Cost effectiveness. The same orthosis is used for the whole duration of treatment, usually about three months.

The Study

A prospective study was therefore undertaken by the author to test the clinical efficacy of this device. All cases were referred to me by primary-care physicians (pediatrician or family practitioner). All children who fitted the following criteria were included in the study:

They were between the ages of two and eight months.
The deformities were moderate or severe, and partially flexible or worse by Bleck's criteria. These were cases that would have needed serial castings. Mild deformities or completely flexible feet (regardless of severity) by Bleck's criteria were excluded from the study.
They returned for regular follow-up for a period of at least six months.

There were 116 children (200 feet) (Table 1) who were studied, 59 of whom were males and 57 females (Table 2) . One-hundred-thirteen feet were classified as moderate, and 87 feet classified as severe by Bleck's criteria (Table 3) . All the feet were partially flexible in differing degrees. No rigid (totally inflexible) feet were encountered in the series. Eighty-four children had bilateral involvement and 32 children were unilateral. This indicated a 72% incidence of bilaterality, compared to 65.6% reported by Bleck.¹ Of the 32 unilateral cases, 23 were left feet and nine were right feet, indicating a preponderance of left feet involvement.

At the initial office visit, the parent was taught to apply the orthosis correctly, to the satisfaction of the physician. Wear was for 24 hours a day, except for half-hour twice a day cleaning, for a period of eight weeks or until complete correction was obtained, whichever was the greater. Then the device was used at night to maintain the correction for four more weeks to prevent recurrence.

The child was seen at two weeks, four weeks, eight weeks, twelve weeks, six months and one year and beyond from the time of initial fitting. At each visit, clinical examination, clinical photographs and foot imprints were taken for objective evaluation of the feet. Clinical photographs, while useful for illustrative purposes, were not as objective as foot imprints for evaluation purposes, and were not routinely used later in the study.

Of the 116 children studied, 38 children had a six month follow-up, 28 children had a one year follow-up, 21 had a 18 months follow-up, 26 had a two year follow-up, and three had a three year follow-up. Average duration of follow-up was 14 and a half months from the time of treatment (Table 4) .

Results

The results of the study have been most encouraging.
(Figure 6 , Figure 7 , Figure 8 , Figure 9 , and Figure 10 ).

All 116 children obtained complete correction with bracing (by Bleck's criteria for correction and flexibility). Of the 200 feet studied, 15 feet (or 7.5°c) obtained complete correction after two weeks of bracing; 59 feet (or 29.5%) obtained complete correction after four weeks of bracing; 111 feet (or 55.5%) obtained complete correction after eight weeks of bracing; and 15 feet (or 7.5%) obtained complete correction after twelve weeks of bracing (Table 5) .

It was interesting to note that while there was no direct correlation between the age of the patient and the duration of bracing required for complete correction, only children four months or younger could obtain complete correction in as little as two weeks (Table 6) . Again, no direct correlation was found between the severity of the deformity and the duration of the bracing required to obtain complete correction, but the less severe deformities responded more readily to bracing. Fourteen of the moderate deformities obtained complete correction after only two weeks of bracing, while only one of the severe deformities responded in two weeks (Table 7) .

The sex of the child did not play a part in determining the severity of the deformity, nor the duration of bracing required to obtain correction (Table 3 and Table 8 ).

The feet remained completely corrected at subsequent follow-ups of up to three years Table 3 , indicating no recurrence.

Complications

Complications and difficulties were encountered, but were not serious in nature:

Skin redness was common over the pressure points at the distal part of the first metatarsal, the heel, and the dorsum of the foot under the foot strap, but were of no consequence. The redness disappeared once full-time orthotic wear was discontinued. There were, however, two cases of skin blistering on the dorsum of the foot due to pressure against the edge of the brace. This was obviated by use of a heat-gun to relieve the edge of the orthosis. Incorporation of a polyethylene foam lining in the device and use of thin cotton or acrylic socks under the orthosis also helped.
Dynamic hallux varus occurred in five cases. In this condition, the foot remained straight, but the great toe tended to turn in when the child stood or walked. When seated or lying down, the great toe returned to its normal direction. This is an often encountered condition even with castings. There is no structural problem involved, and usually the condition clears up spontaneously after a few months. In the series, all five cases resolved on follow-up.
No response to treatment, though not encountered in this present study of 116 children, could be expected if bracing was used in the rarer, totally inflexible or rigid deformities. An attempt at studying the efficacy of the orthosis on this class of deformities is needed. In the meantime, the author's approach is to start bracing as early as possible, and if no improvement is evident after four to six weeks, casting should be used.
Recurrence after correction was not encountered in this present study. The author felt that the best way to prevent recurrence was to continue full-time bracing for eight weeks or till complete correction was obtained, whichever was the greater, and then to maintain the correction using the orthosis at night for four weeks afterwards. Corrective shoes were not found to be necessary.
Circulation problems were not encountered since the whole foot was exposed to view, and the Velcro straps could be easily detached in case of doubt. The infant's parents were always told to call immediately if there was any concern.

Conclusion

In conclusion, a new device has been developed and tested for the treatment of metatarsus adductus in infancy, and has been found to be a very effective alternative to serial castings. Distinct advantages of this corrective brace over castings include safety convenience and dramatic savings in cost and time.

Note: The Wheaton Brace is available through the Wheaton Brace Co., 380 5. Schmare Road, Suite #201, Carol Street, Illinois 60188; tel. 1-800-227-6769.

Andrew Chong. M.D., F.M.C.S.(C), F.A.C.S., presented this paper as a scientific exhibit at the American Academy of Orthopaedic Surgeons Annual Meeting in San Francisco, California, in February 1987. Send correspondence to Andrew Chong, M.D., at 1800 N. Main Street, Wheaton, Illinois 60187. Tel. (312) 665-6200.

References:

Kling, T.F. and R.N. Hensinger, "Angular and Torsinal Deformities of the Lower Limbs in Children," C/in. Orthop., 176, 1983, pp. 136-147.
Bleck, FE., "Metatarsus Adductus: Classification and Relationship to Outcomes of Treatment, J. Pediat. Orth., 3, 1983, pp. 2-9.
Bleck, FE., "Developmental Orthopaedics III: Toddlers," Develop. Med. Child Neurol. 24, 1982, pp. 535-555.
Hensinger, R.N. and E.T. Jones, "Developmental Orthopaedics I: The Lower Limb," Develop. Med. Child Neurol., 24, 1982, pp. 95-116.
Kite, J.H., "Congenital Metatarsus Varus," J. Bone and Joint Surg., 32A, 1950, pp. 500-506.
Kling, T.F. and R.N. Hensinger, "Angular and Torsinal Deformities of the Lower Limbs in Children," pp. 136-147.
Ponseti, IV. and J.R. Becker, "Congenital Metatarsus AdductusäThe Results of Treatment," J. Bone and Joint Surg., 48A, 1966, pp. 702-710.
Tachdjian, M.O., "The Foot and Ankle." Pediatric Orthopaedics, 2, pp. 1323-1342. W.B. Saunders, Philadelphia, 1972.
Bleck, E.E., "Developmental Orthopaedics III: Toddlers," Develop. Med. Child Neurol. 24, 1982, pp. 535-555.
Hensinger, R.N. and E.T. Jones, "Developmental Orthopaedics I: The Lower Limb," Develop. Med. Child Neurol., pp. 95-116.
Kite, J.H., "Congenital Metatarsus Varus," I. Bone and Joint Surg., pp. 500-506.
Kling, T.F. and RN. Hensinger, "Angular and Torsinal Deformities of the Lower Limbs in Children," pp. 136-147.
Ponseti, I.V. and JR. Becker, "Congenital Metatarsus Adductus The Results of Treatment," pp. 702-710.
Tachdjian, MO., "The Foot and Ankle," Pediatric Orthopaedics, pp. 1323-1342.
Kling, T.F. and R.N. Hensinger, "Angular and Torsinal Deformities of the Lower Limbs in Children," pp. 136-147.
Gould, N., "Shoes and Shoe Modifications." Disorders of the Foot, 2, W.B. Saunders, Philadelphia, 1982, pp. 1745-1776.
Hensinger, R.N. and FT. Jones, "Developmental Orthopaedics I: The Lower Limb," pp. 95-116.
Kling, T.F. and RN. Hensinger, "Angular and Torsinal Deformities of the Lower Limbs in Children," pp. 136-147.
Lusskin, R. and H.A. Lusskin, "Metatarsus Varus Splint for the Pre-walker," J. Bone and Joint Surg., 41A, 1959, pp. 363-364.
Hensinger, R.N. and E.T. Jones, "Develop- mental Orthopaedics I: The Lower Limb," Develop. Med. Child Neurol., 24, 1982, pp. 95-116.