Radiographic Assessment of Pediatric Foot Alignment: Review

Transcription

1 JR Integrative Imaging LIFELONG LERNING FOR RDIOLOGY Radiographic ssessment of Pediatric Foot lignment: Review Mahesh M. Thapa 1,2, Sumit Pruthi 1,2, Felix S. Chew 2 Objective The purpose of this article is to discuss the radiographic assessment of pediatric foot alignment. Clinical scenarios are included to orient the learner to the evaluation of pediatric foot alignment. bnormalities discussed include, but are not limited to, talipes equinovarus (congenital clubfoot), planovalgus, and vertical talus. Practice questions are included to assess understanding of the subject matter. Radiographs are a useful tool for assessing alignment disorders of the foot. Complex clinical examination findings and radiographic appearance may warrant further imaging. Malalignment of the bones of the foot may present a complex diagnostic problem for radiologists. In this article, multiple cases illustrating common and a few uncommon abnormalities will be presented. efore more advanced imaging such as ultrasound, CT, and MRI are considered, conventional radiographs are initially obtained in a variety of acquired and congenital disorders of the foot. n Explanation of Technique and Terms lthough some of this information is repeated in the case scenarios to follow, it is helpful to begin by discussing the techniques [1] required to obtain adequate radiographs of the foot. The basic radiographic examination in evaluating any foot deformity consists of weightbearing dorsoplantar (anteroposterior) and lateral views. Nonweightbearing views are inadequate to assess for malalignment because the bones will not be in their functional states. In infants or nonambulatory patients, simulated weightbearing views must be obtained. The dorsoplantar projection is obtained with the child standing, and the tibia should be perpendicular to the film plane. The central ray is angled approximately 15 toward the heel to minimize overlap between the lower leg and the posterior foot. If possible, the lateral projection should also be obtained with the child standing. gain, the tibia should be as perpendicular to the cassette as possible. In nonambulatory patients, plantar pressure can be applied with a plastic board. Hindfoot refers to the talus and calcaneus. The forefoot is composed of the metatarsals and phalanges. Therefore, the cuboid, navicular, and cuneiform bones are considered the midfoot. If we think of the foot as being divided into these three compartments (i.e., forefoot, midfoot, and hindfoot), it will help us develop an organized approach to evaluating any foot radiograph for alignment. First, you can evaluate the relationship of the tibia to the hindfoot, then the relationship of the hindfoot to the midfoot, and finally the relationship of the midfoot to the forefoot. s you read the case scenarios, you will see how this can be a useful method. efore delving into the case scenarios, let us become familiar with the terms used to describe abnormalities in foot alignment. In the hindfoot (Table 1), valgus deformity refers to the widening of the angle between the mid talar and mid calcaneal lines because the mid calcaneal line is deviated away from the midline of the body. Varus deformities occur when the mid calcaneal line is deviated toward the midline of the body from its usual position, decreasing the angle between the mid talar and mid calcaneal lines. oth valgus and varus deformities are best evaluated on the anteroposterior projection. Equinus position results in superior elevation of the posterior part of the foot. With respect to the calcaneus, it is plantar flexed, anterior end lower. Equinus position may also refer to persistent plantar flexion of the entire foot, in which case the calcaneus itself need not be in equinus. When there is increased vertical attitude of the calcaneus, anterior-end higher (the reverse of equinus position), it is the calcaneus position. s a general reference, the lateral tibiocalcaneal angle typically decreases from 77 to 66 from birth to 4 years. In cavus deformity, there is an increase in the depth of the plantar arch (elevated medial longitudinal arch). The plantar arch is formed by the metatarsals and the calcaneus bones. Equinus position, calcaneus position, and cavus deformities are all best evaluated in the lateral projection. Let us now consider terminology commonly used to describe forefoot abnormalities (Table 2). dduction refers to Keywords: foot alignment, pediatrics, radiography DOI: /JR Received November 19, 2008; accepted after revision March 14, Department of Radiology, Seattle Children s Hospital, M/S R-5417 PO ox 5371 Seattle, W ddress correspondence to M. M. Thapa (thapamd@u.washington.edu). 2 Department of Radiology, University of Washington, Seattle, W JR 2010;194:S51 S X/10/1946 S51 merican Roentgen Ray Society JR:194, June 2010 S51

2 Thapa et al. movement of the metatarsals as a unit toward the midline, pivoting at their bases. The movements of the metatarsals are restricted to the plane of the foot (i.e., no inversion or eversion). Conversely, movement of the metatarsals as a unit away from the midline, pivoting at their bases, is called abduction. gain, the movements of the metatarsals are restricted to the plane of the foot (i.e., no inversion or eversion). dduction and abduction are best evaluated on the anteroposterior projection. When the metatarsals are torqued so the sole faces inward, the term inversion (synonyms: varus and supination) is used. On the anteroposterior projection, there is increased superimposition of the metatarsal Scenario I 9-year-old boy presented with generalized foot pain after a fall. Figures 1 and 1 show weightbearing anteroposterior (dorsoplantar) and lateral views of a skeletally immature right foot with normal forefoot and hindfoot alignment. Figures 1C and 1D show a younger child with normal anteroposterior and lateral foot findings for comparison. The tarsal bones are incompletely ossified, but the relationships of the talus and calcaneus to each other and other bones can still be evaluated. TLE 1: Hindfoot lignment Terminology Described With Reference Images Terminology Valgus Varus Equinus position Calcaneus position Cavus Description Mid calcaneal line is deviated away from the midline of the body Mid calcaneal line is deviated toward the midline of the body Superior elevation of the posterior part of the foot with respect to the calcaneus; it is plantar flexed, anterior end lower; equinus position may also refer to persistent plantar flexion of the entire foot Increased vertical attitude of the calcaneus, anterior end higher Increase in the depth of the plantar arch, formed by the metatarsals and calcaneus Reference Images (Figure No.) 2, 5, 6 3, bases. On the lateral projection, there is less overlapping of the metatarsals and they appear as rungs of a ladder, with the fifth metatarsal lowest and the first metatarsal highest. Eversion (synonyms: valgus and pronation) is the opposite of inversion. The metatarsals are torqued such that the sole faces outward. Radiographic changes are often difficult to detect. On the anteroposterior projection, there may be increased separation of the metatarsal bases. On the lateral view, a ladderlike appearance again may be seen, but the reverse of inversion, with the first metatarsal most plantar. In general, however, the ladderlike distortion is rarely as striking as seen in forefoot inversion. The first step (no pun intended) in diagnosing pediatric foot malalignment begins by understanding normal alignment. For accurate assessment, the examination should be performed during weightbearing (or simulated weightbearing), and there must be at least two orthogonal views (e.g., anteroposterior and lateral) [1]. If talocalcaneal coalition is suspected, a Harris view of the calcaneus may also be obtained to better assess the subtalar joint [2]. To obtain the Harris (penetrated axial) view, the patient stands on the cassette and the x-ray beam is angled between 35 and 45 to the cassette. This projection will show the posterior subtalar joint laterally and the sustentacular facet medially. Therefore, this view can reveal coalition between the sustentaculum and the talus at the middle facet, and less commonly, coalition in the posterior facet. s previously mentioned, the talus is the only bone in the foot without a direct muscular attachment. The significance of this fact cannot be overstated. Foot malalignment is often related to neurologic or neuromuscular disorders, such as cerebral palsy, myelomeningocele, and arthrogryposis. Such disorders often lead to abnormal muscle tension. ecause the talus has no direct muscle attachment, it is not as affected as other bones. Therefore, when we see abnormalities in foot alignment, it is helpful to assume the talus is positioned exactly where it should be and all the other bones have moved or repositioned themselves with respect to the talus [1]. On the anteroposterior projection, the mid calcaneal line is drawn parallel to its lateral cortical surface and should intersect the base of the fourth metatarsal. The mid talar line is drawn parallel to its medial cortical surface and should pass through or slightly medial to the base of the first metatarsal. Note: the relationships of these lines to the TLE 2: Forefoot lignment Terminology Described With Reference Images Terminology dduction bduction Inversion (varus and supination) Eversion (valgus and pronation) Description Movement of metatarsals as a unit toward midline, pivoting at their bases Movement of metatarsals as a unit away from midline, pivoting at their bases The metatarsals are torqued so the sole faces inward The metatarsals are torqued so the sole faces outward Reference Image (Figure No.) 4, 6 5 4, 6 5 S52 JR:194, June 2010

3 Radiography of Pediatric Foot lignment shafts of the metatarsals are of no consequence. It is their relationship to the bases that are important. It is also important to note the relationship of the navicular (if it is ossified) to the talus. Normally, the navicular should be positioned directly opposite the talus. Subtle hindfoot malalignment will frequently show varying degrees of talonavicular subluxation. Lastly, pay attention to the degree of overlap of the metatarsal bases. There should be a slight amount of overlap. Too much or too little overlap often indicates forefoot inversion or eversion, respectively. Fig. 1 Generalized foot pain in two children after trauma., nteroposterior (dorsoplantar) weightbearing view in 9-year-old boy with generalized foot pain after fall shows normal talocalcaneal angle. Mid talar line should pass through or just medial to base of first metatarsal. Mid calcaneal line should pass through base of fourth metatarsal. lso note normal position of navicular just opposite talus and slight overlapping of metatarsal bases., Lateral view in same patient as in shows normal talocalcaneal angle. Mid talar line should pass through or be parallel to first metatarsal. Calcaneal line, drawn through its base, shows normal slight plantarflexion of anterior calcaneus. Exact numerical values are not important. lso note degree of overlap of metatarsal shafts. C and D, nteroposterior (C) and lateral (D) weightbearing views in 3-year-old boy with foot pain after minor trauma show normal alignment. lthough tarsal bones are incompletely ossified, relationship of mid calcaneal and mid talar lines is maintained. On the lateral projection, the mid talar line travels through or is parallel to the shafts of the first metatarsal. tangent line drawn along the inferior surface the calcaneus shows the normal position of the calcaneus, which is slightly dorsiflexed anteriorly, forming the posterior portion of the planar arch. Many authors draw this line through the middle of the calcaneus itself. oth methods are equally valid, as the two lines are parallel, and the angle formed with the mid talar line is unchanged. gain, note the degree of overlap of the metatarsals and the relationship of the navicular to the talus. C D JR:194, June 2010 S53

4 Thapa et al. Scenario 2 2-year-old boy presented with a foot deformity and some skin changes at the medial aspect of the talar head. Weightbearing anteroposterior and lateral views of a skeletally immature right foot show hindfoot alignment abnormality (Fig. 2). On the frontal projection, note the mid talar line travels far medial to the base of the first metatarsal, and the mid calcaneal line extends through the base of the third metatarsal. The talocalcaneal angle on the anteroposterior view (Fig. 2), therefore, forms a larger angle than seen in the normal foot. On the lateral projection (Fig. 2), the talus assumes a more vertical position Fig. 2 2-year-old boy with foot deformity and some skin changes at medial aspect of talar head., Weightbearing anteroposterior view of skeletally immature right foot shows mid talar line travels far medial to base of first metatarsal, and mid calcaneal line extends through base of third metatarsal. Talocalcaneal angle on anteroposterior view, therefore, forms more obtuse angle than seen in normal foot (Fig. 1)., In weightbearing lateral view, talus assumes more vertical position than normal and mid talar line does not course through first metatarsal. Scenario 3 7-year-old boy with developmental delay. Weightbearing anteroposterior and lateral views of a skeletally immature right foot (Figs. 3 and 3) show hindfoot alignment abnormality. On the anteroposterior projection (Fig. 3), than normal and the mid talar line does not course through the first metatarsal. In hindfoot valgus, the calcaneus is abducted and rotated away from the talus, with an increased talocalcaneal angle on the anteroposterior projection. This results in apparent medial deviation of the talus, so the mid talar line points medial to the first metatarsal base. In actuality, the talus is positioned where it should be (remember the talus has no muscular attachments); the entire foot under and distal to the talus has been abducted and everted [1]. If the navicular bone is ossified, it will be subluxed laterally from its normal position. On the lateral projection, the talus will assume a more vertical than normal position because it has lost its medial support due to abduction of the calcaneus. note the near parallel alignment of the talus and calcaneus, making the talocalcaneal angle very small or perhaps zero. Decreased talocalcaneal angle can be appreciated on the lateral view (Fig. 3) as well. Compare with normal anatomy (Fig. 1). In hindfoot varus, the calcaneus is adducted and rotated under the talus, reducing the normal plantar angulation of the S54 JR:194, June 2010

5 Radiography of Pediatric Foot lignment Scenario 4 3-year-old boy with foot deformity whose parents claim, the top of the foot is where the bottom should be. Weightbearing anteroposterior and lateral views of a skeletally immature right foot show hindfoot alignment abnormality (Fig. 4). On the anteroposterior projection, note the near parallel alignment of the talus and calcaneus, making the talocalcaneal angle very acute or nonexistent. In the forefoot, there is adduction. The near-parallel arrangement of the talus and calcaneus can be appreciated on the lateral view as well. The lateral view of the forefoot also shows a ladderlike arrangement of the metatarsals, with the fifth metatarsal corresponding to the lowest rung of the ladder. The calcaneus is in equinus, The term talipes is a portmanteau of two Latin words referring to ankle (talus) and foot (pes). In severe cases, patients will literally walk on their ankles [1]. The vernacular term, clubfoot, should be restricted to congenital talipes equinovarus deformity. The term talipes has also been applied to congenital abnormalities of the foot in which the patient does not in any strict sense walk on the ankles. These other conditions include talipes varus, talipes calcaneovalgus, talipes equinovalgus, and talipes calcaneovarus [1]. There is still no definite single cause to explain all forms of congenital talipes equinovarus. Many explanations for the idiopathic form have been proposed. These include defective connective tissue with ligamentous laxity, muscular imbalance, intrauterine positioning deformity, CNS abnortalus. On the anteroposterior projection, the calcaneus appears to be adducted and inverted under the talus, such that the axes through the two bones are more parallel or superimposed, leading to a decreased talocalcaneal angle. ecause the rest of the foot also deviates medially, a line drawn through the talus will point laterally to the first metatarsal base, and the navicular bone will be subluxed medially with respect to the talar head. On the lateral projection, there is a decrease in the talocalcaneal angle and the two bones appear more parallel than normal because the adducted calcaneus uplifts the anterior talus [1]. Hindfoot varus deformity may be associated with a cavus foot deformity (cavovarus). In cavus foot, the forefoot is markedly planar flexed relative to the hindfoot (Fig. 3C). The hindfoot usually exhibits exaggerated dorsiflexion of the anterior calcaneus when the condition is caused by flaccid paralysis from poliomyelitis or myelomeningocele [3]. C Fig. 3 Children with developmental delay and myelomeningocele., Weightbearing anteroposterior view of skeletally immature left foot in 7-year-old boy with developmental delay shows hindfoot alignment abnormality. Note near parallel alignment of talus and calcaneus, making talocalcaneal angle very acute or nonexistent., Weightbearing lateral view of same patient as in shows decreased talocalcaneal angle can be appreciated on lateral view as well. Compare with normal findings (Fig. 1). C, Lateral, weightbearing view in 8-year-old boy with history of myelomeningocele shows markedly increased dorsiflexion of anterior calcaneus and plantarflexion of metatarsals, resulting in cavovarus deformity. with the anterior portion abnormally planar flexed relative to the posterior. JR:194, June 2010 S55

6 Thapa et al. Scenario 5 9-year-old boy presented with medial foot pain. Figure 5 shows hindfoot and forefoot alignment abnormalities. In the 9-year-old boy, weightbearing anteroposterior (Fig. 5) and lateral (Fig. 5) views of the right foot show hindfoot and forefoot alignment abnormalities. On the anteroposterior projection, the mid talar line passes far medial to the base of the first metatarsal and there is lateral subluxation of the navicular on the talus. The mid calcaneal line does not pass through the base of the fourth metatarsal. In the forefoot, there is slight eversion (pronation) of the metatarsals as seen by a decrease in overlap of mality, intrinsic mesenchymal abnormality, and persistence of early normal fetal relationships. Whatever the cause, at radiography congenital talipes equinovarus manifests as severe hindfoot varus and adduction or inversion of the midfoot and forefoot, with the entire foot held in equinus position [1]. Treatment usually starts with nonoperative measures, such as physical therapy and bracing. lthough the success rate of conservative management has been estimated to be low at 5% [2], the Ponseti method appears to have improved it dramatically [4]. study by Herzenberg et al. [5] reported the results in the first 27 patients that they treated with the Ponseti technique and found 97% success, with only one failure (3%), defined as the need for surgical correction of the deformity [5]. Surgical management includes a combination of soft-tissue releases, tendon transfers, and osteotomies [2]. Fig. 4 3-year-old boy with foot deformity and parents claiming, top of foot is where bottom should be., Weightbearing anteroposterior view of skeletally immature right foot shows near-parallel alignment of talus and calcaneus, making talocalcaneal angle very acute or nonexistent. In forefoot, there is adduction., Maximum dorsiflexed lateral view shows near-parallel arrangement of talus and calcaneus can be appreciated on lateral view as well. There is forefoot inversion, as seen by ladderlike arrangement of metatarsals, with fifth metatarsal corresponding to lowest rung of ladder. Entire foot is in equinus. the metatarsal bases compared with the images of the normal foot in Figure 1. On the lateral view, the talus assumes a more vertical orientation than expected, while still maintaining articulation with the navicular. The individual metatarsals are difficult to separate because there is more overlap of their shafts than normal. Note that there is decreased overlap of the metatarsal bases on the anteroposterior projection and increased overlap of the metatarsal shafts in the lateral view. Flatfoot, in general, may be an isolated finding, or it may be one component of a larger pathologic condition such as generalized ligamentous laxity or neurologic and muscular abnormalities [6]. However, it must be noted that flatfoot may be a S56 JR:194, June 2010

7 Radiography of Pediatric Foot lignment Fig. 5 Children with medial foot pain, one with history of cerebral palsy., Weightbearing anteroposterior view of left foot in 9-year-old boy with medial foot pain shows hindfoot and forefoot alignment abnormalities. Mid talar line passes far medial to base of first metatarsal, and there is lateral subluxation of navicular on talus. Mid calcaneal line does not pass through base of fourth metatarsal. There is also slight eversion (pronation) of metatarsals as seen by decrease in overlap of metatarsal bases (compare with normal foot in Fig. 1)., Weightbearing lateral view of same patient as in. Talus assumes more vertical orientation than expected while still maintaining articulation with navicular (star). Individual metatarsals are difficult to separate because there is more overlap than normal of their shafts. C, Weightbearing lateral view of left foot in 8-yearold boy with history of cerebral palsy shows vertical talus and flatfoot deformity. Note complete lack of articulation between talus and navicular (star) in comparison with. Scenario 6 3-year-old girl who presented with foot deformity but no complaints of pain. Weightbearing anteroposterior and lateral views of the right foot (Fig. 6) show forefoot adduction associated with hindfoot valgus, giving the foot a twisted appearance. Radiologically, skewfoot shows significant hindfoot valgus, with lateral subluxation of the navicular on the talus. normal finding in very young children. Pediatric flatfoot can be categorized as either flexible or rigid. For flexible flatfoot, the arch is normal in nonweightbearing and flattened on weightbearing views. Flexible flatfoot may not necessarily be symptomatic. Rigid flatfoot, however, shows stiff arch flattening on both weightbearing and nonweightbearing views. There is frequently an underlying pathology associated with most rigid flatfeet [7]. For example, peroneal spastic flatfoot is a type of rigid flatfoot associated with contraction of the peroneal muscles, frequently seen in patients with tarsal coalition. Planovalgus (a type of flatfoot deformity) does not describe one particular diagnosis. Rather, it is a term to describe a pronated (everted) flatfoot deformity. The mechanism of this deformity involves increased ligamentous laxity, allowing the calcaneus to rotate and be abducted away from beneath the talus. This causes increased weight on the relatively weak medial ligaments. ecause the talar head loses support, it assumes a more vertical orientation, and the plantar arch flattens out [1]. Distally, the metatarsals are angulated medially (in adduction). The mid talar line and a line drawn along the long axis of the first metatarsal will be approximately parallel. third line connecting the mid talar and first metatarsal lines, starting from the center of the talar head and ending at the base of the first metatarsal, will resemble a Z configuration. This is why the skewfoot is also known as Z-foot. Skewfoot is often painless, and it is not rare for skewfoot to be misdiagnosed at birth or very early (less than 1 year) in the child s life. Skewfoot has been initially confused with simple metatarsus adductus and sometimes with talipes equinovarus [8]. Images on next page C JR:194, June 2010 S57

8 Thapa et al. References 1. Ozonoff M. The foot. In: Ozonoff M, ed. Pediatric orthopedic radiology. Philadelphia, P: Saunders, 1992: Harty MP. Imaging of pediatric foot disorders. Radiol Clin North m 2001; 39: Maldjian C, Hofkin S, onakdarpour, Roach N, McCarthy J. bnormalities of the pediatric foot. cad Radiol 1999; 6: Scher DM. The Ponseti method for treatment of congenital clubfoot. Curr FOR YOUR INFORMTION Fig. 6 3-year-old girl with foot deformity but no complaints of pain., Weightbearing anteroposterior view of right foot shows mid talar line and line drawn along long axis of first metatarsal are approximately parallel. third line connecting mid talar and first metatarsal lines starting from center of talar head and ending at base of first metatarsal will resemble Z configuration., Weightbearing lateral view shows that because of valgus malalignment in hindfoot, talus assumes more vertical orientation than normal but still maintains articulation with navicular (circle). Opin Pediatr 2006; 18: Herzenberg JE, Radler C, or N. Ponseti versus traditional methods of casting for idiopathic club foot. J Pediatr Orthop 2002; 22: Hefti F. Foot pain [in German]. Orthopade 1999; 28: Harris EJ, Vanore JV, Thomas JL, et al. Diagnosis and treatment of pediatric flatfoot. J Foot nkle Surg 2004; 43: Napiontek M. Skewfoot. J Pediatr Orthop 2002; 22: The reader s attention is directed to the Self-ssessment-Module for this article, which appears on the following pages. S58 JR:194, June 2010