Pediatric Ankle Valgus 

Fibular development and its impact on the kinematics of the ankle and foot are complex topics.^{[1, 2, 3]} The normal fibula is approximately equal in length to the tibia, but its distal tip extends more caudad. Thus, the fibula acts as a lateral buttress, bearing approximately 15% of the body weight during gait (see Image below). Ankle valgus is an insidious deformity that results in pronation of the foot and medial malleolar prominence. The causes are varied and include neuromuscular disorders, skeletal dysplasias, and clubfeet.^{[4, 5, 6, 7, 8]} Left untreated, this deformity may progress, despite the use of orthotics or corrective shoes, resulting in the medial collapse of the ankle and foot. After skeletal maturity, the only remedy is to perform a supramalleolar osteotomy. However, in growing children, there is the opportunity to intervene by means of guided growth or hemi-epiphysiodesis of the distal medial

tibia.

Related eMedicine topics:

Ankle Arthroscopy

Clubfoot

Skeletal Dysplasia

The focus of this article is to discuss the pathophysiology and evolution of ankle valgus and elucidate the role of guided growth (prior to skeletal maturity) to reverse this problem, without the need for osteotomy. If the physis has closed, an osteotomy will be required.

In the normally aligned extremity, the mechanical axis bisects the knee and ankle, at an angle of 3º with respect to the vertical (gravity). The physes of the tibia and fibula, along with the ankle plafond, are parallel to the floor and perpendicular to gravity. This permits the physeal and articular cartilage chondrocytes to resist compression—a task that they are well suited for—while sparing them from shear forces.

Malhotra devised a grading system that is applicable to children older than 2 years (see Image above).^[8] With reference to children with spina bifida, he discussed the following triad of findings:

1. Proximal migration of the fibular physis
2. Lateral wedging of the distal tibial epiphysis
3. Lateral tilt of the talus

The wedging of the lateral distal tibial epiphysis progresses as the stages increase. The situation is compounded by lateral shift of the ground reaction forces. In addition to the triad, one may observe widening of the distal fibular epiphysis consistent with lateral shift of the ground reaction forces, increased fibular weight-bearing and impingement on the talus-calcaneus laterally. In some cases, there is also widening of the medial clear space of the ankle and an obvious “os subtibiale.”

Frequency

Depending on the etiology, ankle valgus is often bilateral; its overall frequency is unknown. It is far more common than ankle varus and may accompany (or mimic) hindfoot deformities, compounding their management. Developing during childhood, if left untreated, it may become relatively disabling by the time of skeletal maturity.

Ankle valgus, which is rare at birth, may gradually develop because of a variety of conditions, including the following (but not limited to these)^{[7, 8, 9, 10, 11]} :

• Cerebral palsy
• Spina bifida
• Arthrogryposis
• Down syndrome
• Congenital clubfoot^[12]
• Neurofibromatosis
• Hereditary multiple exostoses
• Postaxial hypoplasia
• Skeletal dysplasia
• Posttraumatic events
• Ball-and-socket ankle^[13]

All told, ankle valgus is considerably more common than (bony) ankle varus. Often bilateral, it may be seen in conjunction with other limb malalignment problems, including subtalar valgus (or varus) and genu valgum. When unilateral, it may contribute to relative foreshortening of the limb due to lateral tilt and translocation of the hindfoot. This will not be appreciated on a scanogram; a standing AP radiograph of the ankles is necessary to document its contribution.^{[14, 15]}

Normally, the tip of the fibula is caudad to the medial malleolus, and the fibula serves as a lateral buttress to the ankle, bearing up to 15% of the weight. This preserves a horizontal plafond and ameliorates strain on the deltoid and tibiofibular ligaments.

If the fibula is foreshortened because of developmental, posttraumatic, or iatrogenic causes, the lateral buttress effect is lost. As the ankle tilts and the ground reaction force shifts laterally, the balance changes. The deltoid and interosseous ligaments are subject to strain, and the lateral distal tibial epiphysis is compressed, resulting in characteristic wedging. The distal fibular epiphysis may enlarge, reflecting the Heuter-Volkmann principle as it impinges on the hindfoot and assumes increased weight-bearing stresses (see Image below). This continues in a vicious cycle that is refractory to shoe modification or bracing; eventually, surgical intervention is needed. Ankle valgus may also contribute to progressive outward rotation of the tibia and result in secondary valgus strain on the knee.

In the standing position, the medial malleolus is unduly prominent, and the heel and hindfoot are angled laterally, relative to the calf (see top Image below). A common finding is subfibular tenderness due to impingement. There may be concomitant hindfoot deformity, more commonly planovalgus than cavovarus. Proximally, there may be concomitant genu valgum with a corresponding increase in the intermalleolar distance (see bottom Image below). When the etiology is neuromuscular, the patient may have muscle weakness, imbalance, or contractures.

The indications for treatment of ankle valgus are the presence of related discomfort, excessive shoe wear, and documented progression.

• Bracing: While one may temporize and treat mild deformities with lateral heel wedges, or orthoses of varying designs, the underlying growth disturbance will persist and, likely, will progress. As the child grows and gains body mass, these measures will eventually prove inadequate.
• Osteotomy: One surgical option is to perform a supramalleolar osteotomy. Considering the deformities are often bilateral, the patient will need to be immobilized and non-weight-bearing for 6 weeks. For deformities less than 20 º, a closing wedge osteotomy, leaving the fibula intact, is relatively simple and well tolerated. When the deformity is more than 20 º, it is necessary to cut the fibula and translocate the distal tibia-fibula to restore the mechanical axis. This requires more fixation and carries higher risks.

Unfortunately, depending on the age and etiology, recurrent ankle valgus is common with further growth, and the procedure(s) may need to be repeated.

• Guided growth: As an alternative, guided growth, to redirect the distal tibial physis, is a good option for patients of virtually any age, regardless of the etiology. (See Images below.) A transmalleolar screw or an 8-plate (Orthofix, McKinney, Texas) is necessary. The screw is economical and simple to insert; however, there may be major challenges when it comes time to remove the implant. The 8-plate offers some advantages: It is simple to apply; the flexible tension band offers a fulcrum that is medial to the physis; the correction is more rapid; and the 8-plate is simpler to remove.^[16] Transmalleolar screws, though easy to insert, may be difficult to remove. Shown here are 2 complications: screw breakage and intra-articular migration of the screw head, reflecting the drawbacks of imposing a rigid restraint on a dynamic and growing physis. This patient (see also Image below) failed to return for follow-up for 24 months following medial malleolar epiphysiodeses. There is obvious iatrogenic varus with tenting of the physes and risk of premature closure. (Click Image to enlarge.)These screws were removed (with difficulty) on an urgent basis (see also Image above).

Normal

• Horizontal plafond
• Lateral distal tibial angle (LDTA) is 87 º
• Rectangular-shaped distal tibial epiphysis
• Fibular tip caudal to medial malleolus
• Fibular physis at or below level of the tibial plafond (Malhotra stage 0)
• Medial clear space = superior clear space
• Tibiofibular syndesmosis not widened

Ankle valgus

• Plafond tilted laterally
• Lateral distal tibial angle (LDTA) < 87 º
• Triangular-shaped tibial epiphysis with wedging
• Fibular tip elevated; distal epiphysis broadened
• Fibular physis above plafond (Malhotra stage I, II, or III)
• Medial clear space widened with or without os subtibiale
• Tibiofibular syndesmosis may be widened (HME)

There are no contraindications to the surgical correction of ankle valgus. If the physis is closed an osteotomy is required; if it is open, guided growth is preferred in most circumstances.