Pediatric Ankle Valgus

Normal ankle anatomy (see the image below) has the following characteristics:

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

Ankle valgus has the following characteristics:

• Laterally tilted plafond
• LDTA that is less than 87º
• Triange-shaped tibial epiphysis with wedging
• Elevated fibular tip; broadened distal epiphysis
• Fibular physis above the plafond (Malhotra stage 1, 2, or 3)
• Widened medial clear space, with or without os subtibiale
• Possibly, widened tibiofibular syndesmosis

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).

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).

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] :

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

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.

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.

In the standing position, the medial malleolus is unduly prominent, and the heel and hindfoot are angled laterally, relative to the calf (see the 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 the image below). When the etiology is neuromuscular, the patient may have muscle weakness, imbalance, or contractures.

The most relevant imaging studies include weightbearing anteroposterior (AP) and lateral radiographs of the ankles and feet. In the presence of concomitant limb deformities, a full-length standing AP radiograph of the legs is useful.

Unless a traumatic or other physeal bar is suspected, advanced imaging, such as computed tomography (CT) or magnetic resonance imaging (MRI) is not warranted. At the time of surgery, an arthrogram may be useful in outlining the cartilaginous anlage of the distal tibia-fibula. This is sometimes helpful in young children with skeletal dysplasias.

For generalized conditions, gait analysis may be interesting to document. In particular, comparison of pretreatment and posttreatment pedobarographs may be revealing as foot pronation improves.

There may be an occasional need for consultation by a geneticist or neurologist, especially for children with suspected syndromes. There may also be indications for electromyography (EMG), nerve conduction studies, or muscle biopsy. However, the majority of patients with progressive ankle valgus have well-established and chronic conditions, such as cerebral palsy, spina bifida, and arthrogryposis (amyoplasia).

The staging schema proposed by Malhotra is germane and may be used to document the severity and progression of untreated ankle valgus.[8]  With reference to children with spina bifida, Malhotra discussed the following triad of findings (see the image below):

• Proximal migration of the fibular physis
• Lateral wedging of the distal tibial epiphysis
• 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 weightbearing 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.”

Valgus of up to 6º (normal, 3º) or a lateral distal tibial angle (LDTA) less than 84º (normal, 87º) may be observed unless there are related symptoms. Progressive deformities are frequently encountered as children grow older and will warrant intervention.

Generally, the symptoms correlate with the stage of valgus and include the following:

• Lateral impingement–ankle pain
• Rapid shoe destruction
• Brace intolerance
• Medial skin breakdown (advanced cases)

The indications for treatment of ankle valgus are as follows:

• Presence of related discomfort
• Excessive shoe wear
• Documented progression

There are no contraindications for 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. Medical therapy has no impact on the natural history of ankle valgus.

Although one may temporize and treat mild deformities with lateral heel wedges or orthoses of varying designs, the underlying growth disturbance will persist and is likely to progress. As the child grows and gains body mass, these measures will eventually prove inadequate.

Surgical treatment of ankle valgus has an interesting history. Initially, there was some enthusiasm for fibular-Achilles tenodesis to stimulate fibular growth[19] ; this was mainly applied in patients with evolving ankle valgus resulting from poliomyelitis or spina bifida. However, such tethering procedures afford slow and sometimes erratic correction. By comparison, bony procedures are more predictable and effective.

One surgical option is to perform a supramalleolar osteotomy. Because the deformities are often bilateral, the patient will have to be immobilized and nonweightbearing for 6 weeks. For deformities less than 20º, a closing wedge osteotomy that leaves the fibula intact is relatively simple and well tolerated. When the deformity is more than 20º, 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 of the patient and the etiology of the deformity, recurrent ankle valgus is common with further growth, and the procedure(s) may have to be repeated.

As an alternative, guided growth, aimed at redirecting the distal tibial physis, is a good option for patients of virtually any age, regardless of the etiology. A transmalleolar screw or an eight-Plate (Orthofix, Verona, Italy) 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 eight-Plate offers some advantages over the transmalleolar screw: It is simple to apply; the flexible tension band offers a fulcrum that is medial to the physis; the correction is more rapid; and it is simpler to remove.[20]

The era of rigid physeal constraint (transphyseal screws) may be drawing to a close. The advantages of a flexible tension band[21] are evident in more rapid correction with fewer hardware-related problems. However, plate retrieval is still necessary. Perhaps, in the future, biodegradable implants will become available. The challenges of control and “planned obsolescence” of such implants remain to be elucidated. Guided growth via chemical or electrical manipulation may someday become a reality.

Commonly performed (temporarily) with a transdesmosis screw, distal tibiofibular synostosis is a prophylactic strategy designed to prevent the complication of iatrogenic ankle valgus during lengthening of the tibia and fibula or during fibular harvest for vascularized bone graft procedures. In some conditions, surgeons have actually bone-grafted the syndesmosis, hoping to preserve permanent parity between the distal tibia and fibula. A bony synostosis will not correct ankle valgus, however.[22]

The technology exists to accomplish isolated fibular lengthening, either rapidly with an intercalary graft or gradually with distraction osteogenesis.[23] This technique has associated complications and drawbacks, however. Given the small diameter and the dense cortical nature of the distal fibula, healing may be slow. The focus upon acquired (posttraumatic) fibular shortening in adults need not be extrapolated to children. Basically, if one can provide the latter with a horizontal plafond, correcting ankle valgus, the relative fibular length seems to be unimportant. (See the image below.)

Supramalleolar varus-producing osteotomy is indicated if there is physeal closure or if skeletal maturity has been reached. If the deformity is less than 15º, a simple closing wedge osteotomy, leaving the fibula intact, works well. For larger deformities, including those with rotational deformity, osteotomies of the tibia and fibula may be preferred, with lateral translocation of the distal fragments to preserve the mechanical axis and avoid undue prominence of the medial malleolus. Fixation is either internal, supplemented with a cast, or external, provided by a frame.

Weightbearing is delayed until healing is well under way. Because the procedure is often bilateral, the patient may need to use a wheelchair initially. The many techniques of osteotomy and fixation options are well detailed in standard texts.[24]

Guided growth remains the simplest option. To achieve meaningful correction, there should be at least 1 year of skeletal growth remaining. Younger patients appear to achieve better correction.[25] When there is doubt about the status of skeletal growth, a hand film for bone age may be helpful. With temporary restraint of the medial tibial physis, the lateral aspect of the physis is free to continue growing, rendering the plafond horizontal.[26]

Depending on the etiology, it may be advantageous to allow slight overcorrection amounting to as much as 5º of varus, anticipating the potential for rebound growth. This will delay the need to repeat the procedure after implant removal. The fibula will grow at its own predetermined rate. Thus, even with a horizontal plafond, the fibular station may be elevated. However, this does not seem to adversely affect the clinical outcome. It is not necessary to lengthen the fibula or to fuse it to the distal tibia.

One approach involves insering a single 4.5-mm cannulated screw vertically into the medial malleolus to tether the physis.[27]  This is placed percutaneously and is well tolerated. However, the potential disadvantages may include violation of the physis, relatively slow correction because the fulcrum is within the physis, and problems retrieving the screw[28] after the requisite 18-24 months (or longer). (See the images below.)

A second approach involves the use of an eight-Plate. This two-hole plate is applied in an extraperiosteal position and secured with two cannulated screws. Because it is flexible (nonlocking), does not violate the physis, and provides a medial fulcrum at the center of rotational axis (CORA), the angular correction is more rapid. In addition, hardware retrieval is simple. This technique may be repeated as necessary during growth. There may be asynchronous growth of the short fibula; however, if the plafond is horizontal, this causes no functional problems. It is not necessary to lengthen the fibula or fuse it to the tibia. (See the images below.)

In a retrospective study comparing temporary medial malleolar transphyseal screw (MMS) hemiepiphysiodesis with tension-band plate (TBP) hemiepiphysiodesis for treatment of ankle valgus in skeletally immature patients, Driscoll et al found that both techniques can be successful, that the former technique may correct the deformity more quickly, and that the latter technique may be associated with a lower rate of hardware-related complications.[29]

Operative details

The preoperative clinical examination should include evaluation of the stance-and-gait pattern, with care taken to identify any associated deformities of the extremity (eg, genu valgum, crouch gait, and limb-length discrepancy). Other deformities may have to be addressed at the time of the ankle surgery.

The feet must be carefully assessed for flexibility, deformities, contracture, or muscle imbalance. Corrective foot surgery may be combined with guided growth of ankle valgus. Weightbearing radiographs of the ankles and feet are a prerequisite for intervention.[18]

The following guidelines pertaining to guided growth may prove sufficient for the vast majority of cases of pediatric ankle valgus correction, regardless of the etiology (see the images below)[24] :

• Perform supine (tourniquet control) fluoroscopic imaging
• Localize the distal medial tibial physis, and mark a 2-cm incision
• Infiltrate (optional) with 0.25% bupivacaine with epinephrine
• Incise skin/subcutaneous tissues, but be sure to preserve the periosteum
• Insert a Keith or similar needle into the physis (midsagittal)
• Insert a 12-mm eight-Plate over the needle
• Place the distal (epiphyseal) guide pin first; avoid the joint or physis
• Place the metaphyseal guide pin
• Insert a cannulated 4.5-mm screw over each guide pin (length, 16 or 24 mm)
• It is permitted to mix hardware lengths and colors (all are titanium)
• Remove the guide pins, and countersink the screws into the plate

By design, these titanium plates are nonlocking. Their strength is predicated on their serving as a flexible tension band that can bend as the screws reach their maximum divergence (~30º; most ankle valgus deformities are < 25º). The length of the screw is not critical, as long as it does not violate the far cortex.

Depending on the circumstances, this is typically an outpatient procedure. A soft dressing will suffice. Immediate range of motion and weightbearing are encouraged.

Osteotomy

The potential complications of supramalleolar osteotomy include overcorrection, undercorrection, loss of fixation, would-healing problems, and recurrent deformity.

Guided growth

Occasional problems with hardware retrieval have been eliminated by the use of the eight-Plate. Because of the flexible construct that does not violate the physis, the observed correction is more rapid and hardware removal is simplified.

Biologic

Generally, premature physeal closure will not occur if the periosteum is preserved.

Rebound growth is a poorly understood biologic phenomenon and is not necessarily a reflection of the hardware. As long as the parents are informed beforehand, this complication is readily managed by repeat guided growth if necessary. This is certainly more acceptable than a repeat osteotomy would be.

Overcorrection is a matter of judgment; the author often allows slight overcorrection (up to 5º), which may compensate for flexible or rigid hindfoot valgus. If a patient is lost to follow-up and has more overcorrection, one may remove the eight-Plate and maintain closer observation. To date, the author has not had to reverse the guided growth or perform an osteotomy.

Skin breakdown may occur. In very slender children who are wearing ankle-foot orthoses, it is important to shape and pad the orthoses so as to minimize friction on the medial malleolus. As the valgus improves, the hardware prominence lessens proportionally.

If a wound infection develops, the implant should be removed (temporarily).

Mechanical

Plate breakage has not been observed.

Screw migration may occur. The solution is to redirect the screw percutaneously under fluoroscopic guidance. If a 16-mm screw does not provide sufficient purchase, a 24-mm screw may be used instead.

Screw breakage has not been observed.

In view of the slow growth at the distal tibia, follow-up every 6 months is sufficient. Allow for up to 5º of varus overcorrection, depending upon hindfoot alignment. Remove the plate(s) when the desired correction is obtained. Continue to monitor, and repeat guided growth as needed.