Ankle Valgus in Cerebral Palsy

Transcription

1 Ankle Valgus in Cerebral Palsy Freeman Miller Contents Introduction... 2 Natural History... 2 Treatment... 3 Diagnostic Evaluations... 3 Indications for Intervention... 3 Outcome of Treatment... 5 Complications of Treatment... 5 Conclusion... 5 Cases... 5 Case 1 Silas... 5 Case 2 Lindsey... 7 Case 3 Kenneth... 9 Cross-References References Abstract Valgus deformity of the ankle joint has been well recognized as part of the external rotation planovalgus collapse of the paralyzed foot most commonly seen in spina bifida. This same association has been reported in spastic planovalgus feet of children with cerebral palsy (CP), as an unrecognized contributor of hindfoot valgus. Also, there is a well-defined syndrome of increasing ankle valgus when a section of the fibula is resected for use as bone graft. Although the ankle valgus in spastic feet is not as profound as in the paralyzed foot of spina bifida, it is nevertheless significant in some children. The ankle valgus is rarely an isolated primary deformity in spastic feet, although it may be the primary deformity in rare children who are ambulatory with primary F. Miller (*) AI DuPont Hospital for Children, Wilmington, DE, USA freeman.miller@gmail.com # Springer International Publishing AG, part of Springer Nature 2018 F. Miller et al. (eds.), Cerebral Palsy, 1

2 2 F. Miller hypotonic CP. A common factor in ankle valgus in children with CP is that it is very often missed initially. Ankle valgus is a secondary deformity associated with planovalgus and external tibial torsion. The planovalgus may be appropriately treated but then when the patient still presents with what appears to be a valgus foot during stance phase of gait. The most important aspect of ankle valgus is recognizing when it is present. Treatment options include correction associated with a tibial osteotomy and medial malleolus screw epiphysiodesis. The goal of this chapter is to define the situations where ankle valgus is a problem, how to diagnose it, and the treatment options. Keywords Cerebral palsy Ankle valgus Ankle epiphysiodesis Screw epiphysiodesis Introduction Valgus deformity of the ankle joint has been well recognized as part of the external rotation planovalgus collapse of the paralyzed foot most commonly seen in spina bifida. (Dias 1985) This same association has been reported in spastic planovalgus feet of children with cerebral palsy (CP) (McCall et al. 1985; Scott et al. 1988), as an unrecognized contributor of hindfoot valgus. Also, there is a well-defined syndrome of increasing ankle valgus when a section of the fibula is resected for use as bone graft (Hsu et al. 1972). Although the ankle valgus in spastic feet is not as profound as in the paralyzed foot of spina bifida, it is nevertheless significant in some children (Davids 2010). The ankle valgus is rarely an isolated primary deformity in spastic feet, although it may be the primary deformity in rare children who are ambulatory with primary hypotonic CP. A common factor in ankle valgus in children with CP is that it is very often missed initially. Commonly it is associated with planovalgus and the planovalgus may be appropriately treated but then when the patient still presents with what appears to be a valgus foot during stance phase of gait. The most important aspect of ankle valgus is recognized when it is present. The goal of this chapter is to define the situations where ankle valgus is a problem, how to diagnose it, and the treatment options. Natural History The natural history of ankle valgus in spastic feet is not defined. Based on our experience, the valgus gets worse during late childhood and adolescent growth, then remains stable after the completion of growth. In almost all children with CP, the ankle valgus is a secondary deformity to the primary deformity of a planovalgus foot. The pathomechanics of this deformity appear to be the initial development of a planovalgus foot, usually associated with external foot progression angle and hyperdorsiflexion which places a large moment at the ankle driving it into valgus. This force increases the load on the fibula and the lateral distal tibial growth plate. Since ankle valgus has not been reported as an isolated lesion and is almost always associated as a secondary lesion of planovalgus, and it usually includes external tibial torsion. This abnormal lateral loading also causes the fibula to be shorter as part of the valgus ankle syndrome. When hyper dorsiflexion at the ankle joint is the predominating posture, there may be a primary deformity at the anterior lateral aspect of the distal tibial epiphysis that on initial radiographs may not be apparent and the fibula may not appear short. In these situations, the patient s foot alignment typically looks quite good when the foot is in neutral dorsiflexion

3 Ankle Valgus in Cerebral Palsy 3 plantarflexion or when it is placed into plantarflexion. However, when the foot is dorsiflexed, the hindfoot will fall into valgus and the whole foot will externally rotate through the subtalor joint. This is often associated and first recognized after correction of planovalgus when there has been either a fusion of the hind foot or osteotomies all of which should stabilize and stiffen up the hind foot. In this situation in neutral or plantarflexion, hindfoot alignment and the forefoot alignment relative to the hindfoot is good. In the situation where residual deformity is recognized after the foot has been corrected, the natural history appears to be one of increasing deformity or the deformity remaining the same if the growth plates have closed. In our experience we have never seen this deformity spontaneously resolve. Correction of the deforming force by correcting the planovalgus foot and external tibial torsion is not enough to cause spontaneous correction of the valgus ankle joint in children with growth remaining. However, if both the rotational foot alignment and the hindfoot valgus and forefoot supination are corrected to neutral, the deformity will typically stabilize. To gain stability of ankle valgus deformity also requires that the ankle not be in hyper dorsiflexion during weight-bearing, this seems to create the anterior lateral defect in the distal tibia which can bring on this apparent return of hindfoot valgus. Treatment Diagnostic Evaluations The valgus of the ankle joint cannot be recognized if the appropriate radiographs are not obtained. The correct radiographs are centered on the ankle joint with a long enough image of the tibia above to measure the long axis of the tibia. The rotational position of the ankle should produce an anteroposterior mortise view showing the profile of the talus. Appropriate radiographs include an anteroposterior view of the ankle joint centered on the ankle (Fig. 1). With the common addition of torsional deformities and the goal of wanting to see a radiograph of the whole tibia, very poor images of the ankle joint are often made. Since ankle valgus has not been reported as an isolated lesion and is almost always associated as a secondary lesion of planovalgus and external tibial torsion, specific radiographs have to be ordered of the ankle joint with the mortice view being most important. Since the fibula is often shorter as part of the valgus ankle syndrome, the mortice radiograph also facilitates this assessment. The epiphysis of the normal ankle should be at the level of the ankle joint, but with CP ankle valgus, it is often at the level of the distal tibial epiphysis. Since valgus ankles in some children with spasticity also seem to have a complex rotational malalignment of the talus in the ankle mortise with more foot valgus in dorsiflexion then plantarflexion, additional imaging may be required. Usually, there is more dysplasia of the anterior lateral ankle mortise than the posterior aspect, a difference which can be hard to appreciate on standard mortice view. In this situation, it is best to obtain a CT scan of the ankle joint. This will allow imaging the asymmetry between the anterior lateral and the posterior and middle lateral aspects of the tibial epiphysis (Case 1). Indications for Intervention Because the ankle valgus is almost always a secondary deformity, there is no role for correction of only the ankle valgus unless the primary deformity is or has been corrected. This correction should be part of a reconstruction of a whole problem, which usually includes the planovalgus foot, equinus ankle, hyperdorsiflexion, and

4 4 F. Miller Fig. 1 When planning corrections of foot deformities, especially planovalgus, it is important to obtain anteroposterior radiographs of the ankle mortise to rule out significant ankle valgus as a component of the deformity. The correct radiographic view is not often obtained, as there is a need to view the whole tibia; however, to obtain an accurate view of the alignment of the ankle mortise, the beam should be perpendicular to the ankle joint. If the positioning is such that the beams are very divergent at the ankle joint, accurate assessment of valgus is not possible external tibial torsion. Indications for correction are more than 10 of ankle joint valgus relative to the long axis of the tibia. If the external tibial torsion is being corrected with an osteotomy, no more than 5 of valgus should be tolerated at the ankle joint. If more valgus is present on the postoperative radiograph, the cast should be wedged to correct the deformity (Case 2). The presence of the ankle valgus must be recognized when correcting the hindfoot because it is important to avoid overcorrection of the hindfoot valgus. If no tibial derotation is required, then correction of the ankle valgus can usually be done with a screw epiphysiodesis of the medial malleolus if there is adequate growth remaining. The ankle has to be monitored with radiographs every 4 6 months, and when the valgus has corrected, the screw should be removed (Case 3). For individuals with a closed growth plate, up to 15 of valgus can be accepted if the foot is corrected close to a neutral position below the ankle. This residual ankle valgus causes the foot to fall into external rotation and valgus with increased dorsiflexion, but tends to be less of a problem in individuals who are dependent on orthotics for ankle stability. In this situation, the ankle orthosis should be solid to prevent dorsiflexion during stance phase. Having the ankle valgus corrected is more important in individuals who are high-functioning community ambulators without orthotics or assistive devices. In the situation where the foot has been corrected but the child continues to fall into valgus with hyper dorsiflexion during stance phase and the individual is not tolerating solid ankle orthotics or they wish not to use orthotics, the correction should be considered. For the individual with an open growth plate, consideration of medial ankle epiphysiodesis is reasonable. In this situation, the ankle may be over corrected into some varus (Case 2). For individuals who are skeletally mature, the primary option is joint stabilization.

5 Ankle Valgus in Cerebral Palsy 5 Because this deformity is extremely difficult to correct with osteotomies, our primary treatment has been ankle fusion. It is typical that this deformity occurs in individuals who have ambulatory ability but are not high demand ambulators (Case 1). Outcome of Treatment There are no reports of the outcome of treating valgus deformity in spastic feet. Our experience has been that it is important not to overcorrect the deformity because a little valgus is better tolerated than a little varus. Also, there does not seem to be much loss of correction, although we have not had enough children corrected by the screw epiphysiodesis who have completed growth to be confident of this fact. A stable correction has been reported in several series with a wide variety of other diagnoses but not specifically focused on children with CP. (Beals 1991) (Davids et al. 1997; Stevens and Belle 1997; Tompkins et al. 2012). Complications of Treatment The primary complication from ankle valgus in CP is the failure to make the diagnosis. In many patients, the appearance of ankle valgus has been overlooked until the planovalgus deformity and external tibial torsion have been corrected. Recognizing the presence of ankle valgus in planning the correction of the primary deformities, external tibial torsion and planovalgus, is an important way of avoiding this late surprise. Following screw epiphysiodesis, there have been no reports of premature growth arrests after the screws were removed (Beals 1991) (Davids et al. 1997; Stevens and Belle 1997; Tompkins et al. 2012). No significant complications have been reported from medial ankle epiphysiodesis, and our only complication from correction of ankle valgus was mild overcorrection, leaving this individual with a mild varus foot position. Radiographic correction of the ankle valgus with respect to the distal tibia and the long axis of the tibia usually occurs with the epiphysiodesis; however, correction of the short fibula seldom occurs (Fig. C3.3). Because the important element in the correction is to have neutral ankle joint mortise alignment, it is better to measure the angle of the dome of the talus to the long axis of the tibia. The position of the fibula does not seem to matter. Conclusion Ankle joint valgus in children with cerebral palsy is a secondary deformity that occurs as a response to external tibial torsion and planovalgus. This deformity needs to be recognized during treatment of the primary deformities and when necessary can be easily treated with medial ankle epiphysiodesis. Cases Case 1 Silas Silas is a 17-year-old boy who is 2 years following bilateral triple arthrodesis for correction of planovalgus feet. He is GMFCS III using a posterior walker; however, over the last year the right foot has developed increased valgus, external rotation, and collapse into dorsiflexion during weight bearing (Fig. C1.1). Radiographs of the foot showed solid fusion with good foot alignment (Fig. C1.2); however, a CT Scan of the

6 6 F. Miller Fig. C1.1 Fig. C1.3 Fig. C1.2 Fig. C1.4

7 Ankle Valgus in Cerebral Palsy 7 Fig. C1.5 ankle shows normal alignment at the posterior half of the ankle mortice (Fig. C1.3). The anterior aspect of the ankle shows a severe defect in both the tibia and the talus which allows the ankle to collapse into severe external rotation and valgus with dorsiflexion (Figs. C1.4 and C1.5). The only available treatment for this severe instability is an ankle fusion, which becomes a pantalar fusion due to the earlier triple arthrodesis (Fig. C1.6). Case 2 Lindsey Lindsey, a 10-year-old girl with moderate diplegia, developed a significant internal tibial torsion, Fig. C1.6 which was cosmetically objectionable to her. She and her family desired this to be corrected with a tibial osteotomy. A percutaneous osteotomy was performed with the application of a short-leg cast and a proximal tibial pin. The radiograph in the operating room showed a significant valgus deformity of the ankle (Fig. C2.1), so the cast was wedged while she was still under anesthesia to get her ankle to neutral alignment (Fig. C2.2). In general, a little valgus is better than varus because the subtalar joint can accommodate the valgus better; however, significant valgus may place an external rotation valgus moment on the foot

8 8 F. Miller Fig. C2.1 causing progressive valgus collapse of the foot. The goal should be to have 0 to 5 of valgus at the ankle joint. If after the cast is applied and there is more than 10 of valgus or more than 5 of varus, the cast should be wedged and the angulation corrected. The technique for doing the wedge is to make two lines down the middle of the Fig. C2.2 fragments to be aligned, and this intersection level (Fig. C2.3A) is the level at which the cast wedge is to be placed. The triangle (Fig. C2.3B) defines the size of the angular correction that needs to be made. This technique will correct

9 Ankle Valgus in Cerebral Palsy 9 Fig. C2.3 Fig. C3.1 both displacement and angulation. Also, by measuring the width of the cast on the X-ray at level A (Fig. C2.3A), you can next measure the same distance from the apex on the triangle B (Fig. C2.3B), and at this location the width of the open wedge can be measured. This method allows precutting of a block to hold open the wedge. Case 3 Kenneth Kenneth, a 16-year-old boy with significant growth delay and hypotonia, was evaluated with severe planovalgus foot deformities. He had problems tolerating his AFO. On physical examination, he was hypotonic but could walk without assistance. He had severe planovalgus feet but no muscle contractures. In the operating room his feet were reduced to normal position and fixed with a subtalor fusion, but he still tended to fall into valgus with simulated weight bearing. Under fluoroscopy, he was thought to have mild instability of the ankle joint and approximately 10 to 15 of ankle valgus, but he had no torsional malalignment. He had significant amount of growth remaining so a medial malleolar epiphysiodesis screw was placed (Fig. C3.1). He was then monitored carefully, and by the 24-month follow-up, he had acquired approximately 20 of correction, (Fig. C3.2). which could be monitored as well by the presence of a faint growth arrest line (Fig. C3.3). The screw was

10 10 F. Miller Fig. C3.3 References Fig. C3.2 then removed when he had slight overcorrection and the foot appeared in a good position. Cross-References Planovalgus Foot Deformity in Cerebral Palsy Tibial Torsion and Knee Instability in Cerebral Palsy Beals RK (1991) The treatment of ankle valgus by surface epiphyseodesis. Clin Orthop 266 SRC GoogleScholar: Davids JR (2010) The foot and ankle in cerebral palsy. Orthop Clin North Am 41: Davids JR, Valadie AL, Ferguson RL, Bray EW III, Allen BL Jr (1997) Surgical management of ankle valgus in children: use of a transphyseal medial malleolar screw. Orthop 17 SRC GoogleScholar:3 8 Dias LS (1985) Valgus deformity of the ankle joint: pathogenesis of fibular shortening. Orthop 5 SRC GoogleScholar: Hsu LC, Yau AC, O Brien JP, Hodgson AR (1972) Valgus deformity of the ankle resulting from fibular resection for a graft in subtalar fusion in children. Joint Surg Am 54 SRC GoogleScholar: McCall RE, Lillich JS, Harris JR, Johnston FA (1985) The Grice extraarticular subtalar arthrodesis: a clinical review. Orthop 5 SRC GoogleScholar: Scott SM, Janes PC, Stevens PM (1988) Grice subtalar arthrodesis followed to skeletal maturity. Orthop 8 SRC GoogleScholar: Stevens PM, Belle RM (1997) Screw epiphyseodesis for ankle valgus. Orthop 17 SRC GoogleScholar:9 12 Tompkins M, Eberson C, Ehrlich M (2012) Hemiepiphyseal stapling for ankle valgus in multiple hereditary exostoses. Am J Orthop (Belle Mead NJ) 41: E23 E26