Operative Techniques in Orthopaedic Surgery (4 Volume Set) 1st Edition

147. Hemi-Epiphysiodesis for Ankle Valgus

Peter M. Stevens

DEFINITION

images Ankle valgus is a lateral and upward slope of the tibiotalar joint resulting in foot pronation and sometimes lateral translocation of the talus relative to the tibia.

images In the anteroposterior (AP) plane, the weight-bearing axis and ground reaction force fall lateral to the virtual center of the joint. This may perpetuate the cycle of growth inhibition and progressive valgus.

ANATOMY

images Normal alignment of the ankle involves a horizontal plafond, with a lateral distal tibial angle of 0 to 3 degrees (FIG 1).

images Accordingly, the fibula normally bears 15% of body weight.

images The talus lies sandwiched between the malleoli, stabilized by the deltoid ligament medially and the talofibular and calcaneofibular ligaments laterally.

images In the growing child, the fibular physis lies at or distal to the plafond.

images The physes and plafond lie parallel to the floor and perpendicular to the ground reaction forces.

images

FIG 1  A. In the normal ankle, the longer fibula provides a lateral buttress and bears 15% of body weight. Its physis is at or below the level of the plafond.1 The ground reaction force (GRF) bisects the ankle, crossing the joint and tibial physis, which are parallel to the ground. B. When the fibula is foreshortened, the lateral buttress effect is lost and the GRF shifts laterally. There is wedging of the tibial epiphysis (Hueter-Volkmann effect) and the plafond tilts laterally. The distal fibular epiphysis broadens owing to impingement of the hindfoot, as a result of increased weight bearing. There may be medial ankle joint widening due to traction.

PATHOGENESIS

images The common denominator of ankle valgus is a fibula that is relatively foreshortened and fails to buttress the lateral tilt and shift of the talus during weight bearing.

images As the fibular epiphysis bears more than the customary 15% of body weight, it may expand owing to the Hueter–Volkmann effect (another example of form following function).

images As the ground reaction force is displaced laterally, the compression of the lateral distal tibial physis exceeds its tolerance and inhibits normal growth, not only of the physis, but of the epiphysis as well (Hueter–Volkmann effect).

images There may be widening of the medial clear space due to attenuation of the deltoid ligament.

images Subject to chronic and unremitting medial tension, there may be delayed or fragmented ossification of the medial malleolus.

images The physes remain horizontal and perpendicular to gravity.

images With lateral tilt of the talus, shear forces are introduced and articular cartilage attrition may ensue, commencing at the lateral corner of the ankle.

images Subtalar valgus alignment or instability may develop and exacerbate the clinical deformity.

images Concomitant genu valgum imposes an eccentric load on the ankle and may compound the alignment problems (hereditary multiple exostoses, clubfeet; FIG 2).

NATURAL HISTORY

images The natural history of ankle valgus typically is insidious and progressive. It may be noticed around school age and becomes self-perpetuating.

images The natural history is unaffected by corrective shoes or bracing (FIG 3).

images In some conditions (spina bifida, cerebral palsy), there may be skin breakdown over the medial malleolus with attempts to control valgus by bracing.

images Left unattended, the ultimate method of salvage may require a supramalleolar osteotomy.

images This can be avoided by means of medial malleolar epiphysiodesis using a transmalleolar screw or an eight-plate (FIG 4).

PATIENT HISTORY AND PHYSICAL FINDINGS

images Typically the parents have noted chronic, progressively flat or pronated feet.

images Asymmetric and accelerated shoewear is common.

images Activity-related pain is typically lateral, beneath the fibula, as a result of impingement on the talus or calcaneus.

images There may be medial pain, presumably due to tension on the deltoid ligament or to brace irritation.

images Concomitant knee or hindfoot valgus will exacerbate the symptoms.

images

FIG 2  A. Ankle valgus may be mistaken for (or coexist with) planovalgus deformity of the foot. This patient had progressive ankle valgus 6 years after Cincinnati clubfoot reconstruction. Note the prominent medial malleoli. B.This teenager with paralytic ankle valgus (spina bifida) had concomitant genu valgum. Note the increased intermalleolar distance.

images While orthotics may provide support, they will have no beneficial effect. As the deformity progresses, brace tolerance diminishes.

images The clinician should observe the patient's stance from the hindfoot position.

images The patient's knee alignment is observed. Genu valgum or circumduction gait exacerbates hindfoot loading.

images

FIG 3  While orthoses may provide comfort and extend shoewear, they will have no effect on the natural history of ankle valgus.

images

FIG 4  The focal hinge effect provided by an eight-plate to correct valgus deformity. A. The nonlocking screws are free to swivel as lateral growth restores the ground reaction force to neutral. B. This flexible construct permits more rapid correction than the rigid transphyseal screw, without compromising the physis, and it is easier to remove.

images The patient's gait pattern, medial–lateral ankle stress (secondary medial laxity may be evident), and sagittal strength and range of motion (equinus or calcaneus may need treatment) are observed.

images The foot is examined to determine whether an orthotic or surgical treatment is needed.

IMAGING AND OTHER DIAGNOSTIC STUDIES

images Radiographs

images Weight-bearing AP and lateral views of the ankles

images Weight-bearing AP lateral of the feet to assess subtalar alignment

images Weight-bearing AP of the lower extremities, if there is perceived valgus or varus deformity of the knee

images EMED foot pressure studies (optional)

images CT scan or MRI if a distal tibial physeal bar is suspecte.

images CT scan of the foot if a concomitant tarsal coalition is suspected

DIFFERENTIAL DIAGNOSIS

images The deformity is often bilateral: some of the conditions that are known to result in progressive ankle valgus include the following.

images Neuromuscular

images Cerebral palsy

images Spina bifida

images Neurofibromatosis

images Hereditary—growt.

images Hereditary multiple exostoses

images Multiple epiphyseal dysplasia

images Genetic

images Down syndrome

images Other syndromes

images Traumatic

images Clubfoot

images Idiopathic

images The underlying diagnosis (see above) has often been established, but the underlying cause has little relevance to the treatment. The degree of deformity and the evolution of symptoms dictate the timing and need for intervention.

NONOPERATIVE MANAGEMENT

images Activity restriction and nonsteroidal anti-inflammatories are not helpful.

images Physical therapy remedial exercises are of no benefit.

images Soft orthoses or UCB inserts are temporizing means of reducing foot discomfort and extending shoewear.

images They are relatively more efficacious for subtalar instability than ankle valgus.

images They will not effect any growth modulation or improvement in skeletal alignment, however.

SURGICAL MANAGEMENT

images The indications for surgery relate to the evolution of activity-restricting pain.

images Valgus may be manifest in children under age 10 but is more prevalent during the adolescent growth spurt.

images Many patients have already exhausted nonoperative options, such as shoewear modifications, nonsteroidal antiinflammatories, and activity restriction.

Preoperative Planning

images Both the clinical examination and appropriate weight-bearing radiographs should verify the presence and magnitude of valgus deformities, not only of the ankles but also (occasionally) of the hindfeet and knees as well.

images In specific conditions, multilevel surgery may be indicated.

images When the cause involves neuromuscular conditions, concomitant muscle imbalance may warrant combined procedures such as gastrocnemius recession or tendon transfer.

images When available, a pedobarograph may be useful for documenting pathologic foot stresses.

Positioning

images The patient is positioned supine on the operating table.

images The mini or standard C-arm may be used.

images Calf or thigh tourniquets are optional, at the discretion of the surgeon.

Approach

images For a transmalleolar screw, a 5-mm transverse incision below the tip of the medial malleolus will suffice.

images For plate correction, a vertical 12-mm incision over the medial distal tibial physis is optimal.

images The dissection is subcutaneous, with preservation of the periosteum.

images The only nearby neurovascular structures are the saphenous nerve and vein. These are anterior to the incision and easily avoided.

images Supramalleolar osteotomy is the option of last resort.

TECHNIQUES

MEDIAL MALLEOLAR SCREW HEMIEPIPHYSIODESIS

images  With the patient supine and a calf tourniquet inflated (optional), the tip of the medial malleolus is palpated and a 5-mm transverse incision is marked.

images  The subcutaneous tissues may be injected with 0.25% Marcaine.

images  The incision is made sharply and deepened with a hemostat, spreading the subcutaneous tissues down to the tip of the malleolus.

images  A vertical 1.6-mm guidewire is driven upward, with care taken to avoid the ankle mortise.

images  Its trajectory should be vertical, so that the screw will be just lateral to the medial cortex.

images  The more peripheral the fulcrum, the more efficient and rapid the correction will be.

images  The C-arm is used to check the guidewire placement in the AP, mortise, and lateral projections.

images  The tip of the malleolus is drilled with a 3.2-mm cannulated drill bit and a single 4.5-mm cannulated, fully threaded, cortical screw 40 to 50 mm in length is inserted (no washer is necessary; TECH FIG 1).

images  The guidewire is removed and the screw should be tightened so that the screw head is not prominent. However, if the head is buried, the screw may be hard to retrieve in the future.

images  The wound is closed with 4-0 Monocryl sutures and covered with Steri-Strips, OpSite, and an Ace bandage.

images

TECH FIG 1  A. Transphyseal cannulated 4.5-mm screw insertion is performed percutaneously over a 1.6-mm guide pin for accuracy. The ideal fulcrum is near the medial cortex of the tibia for maximal angular correction. Screw removal is facilitated using the guide pin to seat the screwdriver. B. The growth line (arrows) indicates the angular correction achieved to restore a horizontal plafond. Note the downward slope of the physis and the slight bend in the screw, consequent to the intraphyseal fulcrum and the considerable forces of growth on a rigid implant.

GUIDED GROWTH USING AN EIGHT-PLATE

images  With the patient supine and under tourniquet control, the distal medial tibial physis is identified using the image intensifier.

images  A 12-mm incision is marked in the skin and (optionally) injected with 0.25% Marcaine.

images  The incision is made sharply, carrying the dissection through the subcutaneous tissues, with care taken to avoid injury to the periosteum (TECH FIG 2A).

images  A Keith needle is inserted into the physis and its position is checked with the C-arm (TECH FIG 2B).

images  A 12-mm eight-plate is inserted, placing its center hole over the needle, and applied extraperiosteally (TECH FIG 2C).

images  1.6-mm smooth guide pins are inserted, first into the epiphysis and then the metaphysis, avoiding the ankle joint and physis (TECH FIG 2D).

images  The cortex is drilled to a depth of 5 mm using the cannulated 3.2-mm drill.

images  Fully threaded, cannulated screws are then inserted (TECH FIG 2E). For the ankle, the 16- or 24-mm screws may be used. There is no particular advantage to the short (16-mm) screw, but sometimes there is not sufficient room for the 24-mm one. The screws do not have to match or to be parallel.

images  After the plate and screw positions are confirmed on the AP and lateral views, the guide pins are removed and the screws are countersunk into the plate (TECH FIG 2F).

images  After routine wound closure, a soft compression dressing is sufficient.

images

TECH FIG 2  A. For the eight-plate technique, a 12-mm medial incision is made, preserving the periosteum. B. The physis is localized with a Keith needle. C. The eight-plate is slipped over the needle to center this on the physis. D,E. Two 1.6-mm guide pins are inserted parallel to the physis, followed by the self-tapping, cannulated, fully threaded 4.5-mm screws. F. The guide pins are removed and the screws countersunk into the plate. Shown here are 24-mm screws; the alternative is to use the 16-mm screws.

SUPRAMALLEOLAR OSTEOTOMY (SKELETAL MATURITY)

images  An incision is made over the medial metaphyseal flare of the tibia.

images  Kirschner wires are inserted to guide the saw or osteotome, and the surgeon triangulates for the closing wedge.

images  The tibia is cut, leaving lateral cortex intact if possible.

images  The fibula is left intact unless the surgeon intends to correct more than 20 degrees of rotation.

images  The tibial wedge is removed.

images  Smooth, crossed Steinmann pins or plate fixation is used to stabilize = tension band vs. intact fibula.

images  A below-knee cast is applied and the patient is kept nonweight bearing for 4 weeks.

images

POSTOPERATIVE CARE

images Hemiepiphysiodesis

images No immobilization is required.

images Immediate weight bearing is permitted.

images There are no activity restrictions.

images Follow-up is at 6-month intervals with weight-bearing AP radiographs of the ankles.

images The implant is removed when the plafond is horizontal, regardless of fibular length.

images Supramalleolar osteotomy

images The patient uses a cast and crutches for 1 month.

images The patient can use a 3D boot for the second month.

images Implants are removed after healing.

OUTCOMES

images Initially there is no visible difference, and the family needs to be aware of this.

images The correction is slow and subtle, so routine follow-up (every 6 months) is imperative.

images Correction to neutral, or slight varus, will take 12 to 24 months on average.

images The implant is removed on correction of the valgus deformity.

images Follow-up should continue until maturity to watch for recurrent deformity.

images Premature physeal closure is exceedingly unlikely.

COMPLICATIONS

images Complications are predominately related to the transphyseal screws, which are rigid, transgressing the physis and pitted against the dynamic forces of growth (FIG 5).

images

FIG 5  A. On the left, the physis blew past the retained screw. B. As a result of stripping, this screw spun in place, migrated proximally, and could not be removed. C. As the valgus deformity corrected, this screw head ended up within the ankle, notching the talus (with pain) and proved challenging to retrieve. D. This patient failed to return before overcorrecting into varus. E. The screw could not be removed, necessitating a corrective opening wedge osteotomy (through the screw). F. This 17-year-old boy with Marfan syndrome presented with a bent implant and varus overcorrection. Luckily his hindfoot valgus compensated and no osteotomy was needed.

images

FIG 5  G. After 3 years' absence, this 11-yearold autistic boy returned for follow-up with symptomatic ankle varus. The screws were removed with some difficulty, and time will tell if there is sufficient rebound growth to avert osteotomies.

images Stripping, bending, or breakage of the transphyseal screw may make implant removal difficult or impossible.

images If the physis closes in the presence of varus deformity, the only recourse is a corrective osteotomy.

images Compared to the transphyseal screw, the medial plates are easier to locate and remove.

REFERENCES

· Malhotra D, Puri R, Owen R. Valgus deformity of the ankle in children with spine bifida aperta. J Bone Joint Surg Br 1984;66B:381–385.

· Stevens P. Effect of ankle valgus on radiographic appearance of the ankle. J Pediatr Orthop 1988;8:184–186.

· Stevens P, Aoki S, Olson P. Ball and socket ankle. J Pediatr Orthop 2006;26:427–431.

· Stevens P, Belle R. Screw epiphysiodesis for ankle valgus. J Pediatr Orthop 1997;17:9–12.

· Stevens P, Otis S. Ankle valgus and clubfeet. J Pediatr Orthop 1999;19:515–517.

· Tickle C. Genetics and limb development. Develop Genet 1996;19:1–8.



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