Practice Essentials
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. 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 dysplasia, and clubfoot. [4, 5, 6, 7, 8]
The indications for treatment of ankle valgus are as follows:
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Presence of related discomfort
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Excessive shoe wear
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Documented progression
Medical therapy has no impact on the natural history of ankle valgus. There are no contraindications for surgical correction of ankle valgus. 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 hemiepiphysiodesis of the distal medial tibia.
This article focuses on discussing the pathophysiology and evolution of ankle valgus and elucidating 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.
Anatomy
Normal ankle anatomy (see the image below) has the following characteristics:
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Horizontal plafond
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Lateral distal tibial angle (LDTA) of 87º
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Rectangle-shaped distal tibial epiphysis
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Fibular tip caudal to the medial malleolus
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Fibular physis at or below the level of the tibial plafond (Malhotra stage 0 [see Workup])
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Medial clear space equal to superior clear space
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Tibiofibular syndesmosis that is not widened
Normal ankle alignment. The lateral distal tibial angle (LDTA) is 87º, and the fibular physis is at or distal to the level of the plafond, which is horizontal and, thus, perpendicular to gravity.
Ankle valgus has the following characteristics:
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Laterally tilted plafond
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LDTA that is less than 87º
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Triange-shaped tibial epiphysis with wedging
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Elevated fibular tip; broadened distal epiphysis
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Fibular physis above the plafond (Malhotra stage 1, 2, or 3)
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Widened medial clear space, with or without os subtibiale
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Possibly, widened tibiofibular syndesmosis
Pathophysiology
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 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.
The alignment of the tibial and fibular physes, along with the ankle plafond, parallel to the floor and perpendicular to gravity permits the physeal and articular cartilage chondrocytes to resist compression—a task for which they are well suited—while sparing them from shear forces.
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 weightbearing stresses (see the image below).
Lateral impingement may be due to ankle valgus, hindfoot valgus, or both. This is an extreme example.
This process continues in a vicious circle 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.
The severity and progression of ankle valgus may be assessed on the basis of the Malhotra grading system (see Workup).
Etiology
Ankle valgus, which is rare at birth, may gradually develop because of a variety of conditions, including (but not limited to) the following [7, 8, 9, 10, 11] :
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Hereditary multiple exostoses [13]
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Postaxial hypoplasia
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Skeletal dysplasia
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Posttraumatic events
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Ball-and-socket ankle [14]
In a retrospective study by Burghardt et al, ankle valgus was found to have developed postoperatively in 55.8% of feet in a group of pediatric patients who had undergone surgery for idiopathic clubfoot. [15]
A retrospective analysis by Agarwal et al evaluated valgus deformities at the donor leg after harvest of nonvascularized fibular graft in 30 ankles from 23 patients (average age, 9.56 years), all of whom were followed for at least 2 years after the index procedure. [16] Radiologic valgus deformity was noted in in 10 of the ankles (33%).
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 as a consequence of lateral tilt and translocation of the hindfoot. This will not be appreciated on a scanogram; a standing anteroposterior (AP) radiograph of the ankles is necessary to document its contribution. [17, 18]
Epidemiology
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.
Prognosis
As ankle valgus corrects, bracing is facilitated or (in some cases) obviated, and shoewear improves. Lateral impingement and subfibular pain are ameliorated.
Compared to the knee, where rapid improvement is noted, the ankle grows slowly. This is especially true in patients with neuromuscular compromise or skeletal dysplasias. Nevertheless, over the course of 18-24 months, most children will manifest signs of clinical and radiographic improvement. The flexible extraphyseal implant may be left in situ longer, if necessary. The theoretical risk of physeal closure is progressive ankle varus (not encountered to date); this may be remedied with an opening wedge supramalleolar osteotomy.
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Normal ankle alignment. The lateral distal tibial angle (LDTA) is 87º, and the fibular physis is at or distal to the level of the plafond, which is horizontal and, thus, perpendicular to gravity.
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Malhotra classified progressive ankle valgus, which is directly proportional to the degree of fibular physis elevation (stage 0 = normal). The described triad of fibular physis elevation, wedging of the lateral tibial epiphysis, and ankle tilt may be accompanied by horizontal expansion of the fibular epiphysis (impingement), medial clear space widening, and avulsion injuries of the tip of the medial malleolus.
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Lateral impingement may be due to ankle valgus, hindfoot valgus, or both. This is an extreme example.
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One needs to differentiate between ankle valgus (shown here) and hindfoot valgus. It is imperative to obtain a standing anteroposterior radiograph of the ankle when evaluating foot problems.
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Patients may have valgus at more than just the hindfoot and ankle. This boy with congenital clubfeet has genu valgum compounding his gait problems.
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Transmalleolar screws, though easy to insert, may be difficult to remove. Shown here are two 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.
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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.
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These screws were removed (with difficulty) on an urgent basis (see also image above).
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This patient had asynchronous medial malleolar epiphysiodeses. The screw on the left could not be retrieved. His opening wedge osteotomy to correct iatrogenic varus collapsed into a nonunion, necessitating salvage with a Taylor spatial frame. This unfortunate sequence would not have happened with an eight-Plate.
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A drawback of the intraphyseal fulcrum is the rigid constraint of the physis. Correction is relatively slow and inefficient when compared to the flexible, extraphyseal eight-Plate.
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The nonlocking eight-Plate is placed superficial to the intact periosteum. As lateral growth occurs, the screws diverge, permitting safe and gradual correction of the valgus deformity. The ground reaction force moves medially, toward the center of the ankle. The distal tibial physis can expand and grow laterally; the articular cartilage is spared from harmful shear forces.
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The fibula may not respond in a synchronous manner. However, as lateral impingement is alleviated, symptoms abate and there are no functional consequences. In children, it is not necessary to lengthen the fibula or fuse it to the distal tibia.
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Through a 2.5-cm incision, one can place a Keith needle into the distal tibial physis, preserving the periosteum. Center the eight-Plate on the physis, and secure it with the 4.5-mm cannulated screws (either 16 or 24 mm). Place the epiphyseal screw first, with care to avoid the ankle joint or physis.
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Fluoroscopic sequence showing the steps. The 24-mm screws are preferable if there is enough space to insert them.
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Sick physes are not a contraindication to medial malleolar epiphysiodesis, even with screws. Note the remodeling of the distal tibial epiphysis as the ground reaction force is restored to neutral and the plafond rendered horizontal.
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Ankle valgus is relatively common in children with previously operated clubfeet. While these feet may be presumed to be overcorrected, ankle films may reveal ankle valgus and lateral impingement. If the feet are flexible, it may be preferable to deliberately overcorrect into 5º of ankle varus before removing the plates. Continue to observe the child annually until maturity, and repeat as needed.
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Presenting with an anterolateral bow and initially intact fibula, this child went on to a fibular fracture/pseudarthrosis and ankle valgus by age 3 years. Note the medial widening. It is not necessary to fix, bone-graft, or lengthen the fibula, nor is it helpful to create a tibia-fibular synostosis.
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The medial malleolar screw was placed at age 4 years, and over the ensuing 2 years, the valgus corrected into slight varus. This procedure was repeated at age 7 years and again at 9 years, employing the eight-Plate.
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This 12-year-old boy with hemiplegia underwent a rotational supramalleolar osteotomy. Despite the fibula being left intact, he drifted into valgus over the ensuing year.
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This 10-year-old boy demonstrates the stigmata of hereditary multiple exostoses, with concurrent knee and ankle valgus. These deformities were managed by eight-Plates applied to the distal medial femora and distal medial tibiae. The deformities corrected over the ensuing year, and the plates were then removed.
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This 9-year-old patient with spina bifida had progressive and symptomatic ankle valgus. One year following eight-Plate insertion, it is evident that the 16-mm screws are losing their grip. The goal was to achieve slight varus overcorrection.
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In this patient (see also image above),the plates were moved distally and resecured with 24-mm screws.
