BASIC PRINCIPLE #1
Techniques change, but principles are forever.
Therefore, study principles! A principle is a basic generalization that is accepted as true and can be used as a basis for reasoning or conduct. There are many principles of assessment and management of foot deformities and malformations in children and adolescents that need to be appreciated and routinely utilized.
BASIC PRINCIPLE #2
A thorough knowledge of the normal anatomy of the child’s foot is mandatory as the foundation for the assessment and management of foot deformities in children.
There are 26 bones and at least 19 major joints in a foot. The 52 bones in both feet represent 25% of all the bones in the body. Before treating deformities and malformations of the child’s foot, whether nonoperatively or operatively, a thorough and working knowledge of the normal anatomy of the adult foot and ankle is required. Get a good anatomy book and study it. There are many available, but my favorite is Sarrafian’s Anatomy of the Foot and Ankle. (See 3rd edition by Kelikian AS, editor. Philadelphia, PA: Lippincott Williams & Wilkins; 2011.) A thorough and working knowledge of the normal anatomy of the child’s foot and ankle must then be acquired. Although all the same bones, joints, ligaments, muscles, and tendons are present in children and adults, the bones and joints are frequently aligned differently in the two age groups. To my knowledge, no anatomy book exists that is devoted exclusively to the normal child’s foot and its variations, so read on and you will learn what you need to know.
BASIC PRINCIPLE #3
The average normal foot shape in children is different than the average normal foot shape in adults.
And the range of normal foot shapes in children is different than the range of normal foot shapes in adults, though with significant overlap between age groups. For example, many or most babies are flatfooted, a shape less commonly seen in adults. Many babies have metatarsus adductus, a shape rarely seen in adults.
BASIC PRINCIPLE #4
Age-related anatomic variations in the shape of the foot and the natural history of each one must be appreciated.
This basic principle is a corollary of Basic Principle #3. In most cases, anatomic variations in the shape of the child’s foot change spontaneously to adult norms through normal growth and development.
For example, most babies are flatfooted, whereas about 25% of adults are flatfooted (Figure 2-1). Approximately 1 in 100 babies have metatarsus adductus, almost none receive treatment, and very few adults have that foot shape (Figure 2-2).
Knowledge of anatomic variations and their natural history should prevent unnecessary and potentially harmful interventions.
Figure 2-1. A. Footprints from individuals of all ages show that children are more flatfooted than adults, there is a wide range of normal arch heights, and the arch generally elevates spontaneously during the first decade of life. (From Staheli LT, Chew DE, Corbett M. The longitudinal arch. A survey of eight hundred and eighty two feet in normal children and adults. J Bone Joint Surg Am. 1987;69:426–428, with permission.) B. Radiographs from children of all ages confirm the footprint data. The drawing and graph represent the lateral talus–1st metatarsal (so-called Meary’s) angle. (From Vanderwilde R, Staheli LT, Chew DE, et al. Measurements on radiographs of the foot in normal infants and children. J Bone Joint Surg Am. 1988;70:407–415, with permission.)
BASIC PRINCIPLE #5
“The foot is not a joint!” In all congenital and developmental deformities and most malformations of the child’s foot, there are at least two segmental deformities that are often in rotationally opposite directions from each other, “as if the foot was wrung out” (Figure 2-3).
I conceived of, and published, these two phrases many years ago and continue to believe that they accurately and simply convey two important realities. Before one can surgically treat the pain and disability associated with foot deformities and malformations, each segmental deformity and malformation must be identified, characterized, and understood so that a plan can be created to individually, yet concurrently, manage each one.
Figure 2-2. A. Anteroposterior (AP) radiograph of a baby’s foot demonstrating forefoot adductus. (Some might argue that this is a skewfoot, though the strict differentiation of the two deformities in infancy has not been established.) B. AP radiograph of the same baby’s foot 11 months later. The adductus has almost completely resolved without any treatment. NOTE: X-rays are not recommended to make or confirm the diagnosis of congenital metatarsus adductus in infants (see Metatarsus Adductus, Chapter 5).
The rotationally opposite deformities are perhaps best appreciated in the cavovarus foot in which there are hindfoot varus and forefoot pronation, and the flatfoot in which there are hindfoot valgus and forefoot supination (Figure 2-3).
BASIC PRINCIPLE #6
One must understand subtalar joint positions and motions in a manner that supersedes the confusing and inconsistent terminology in the literature.
The static deformity positions of the subtalar joint can appropriately be described using the terminology used for other joints, i.e., varus (the calcaneus angles inward in relation to the talus) and valgus (the calcaneus angles outward in relation to the talus) (Figure 2-4).
Hindfoot varus is the static position of the subtalar joint found in cavovarus feet and clubfeet. Hindfoot valgus is the static position of the subtalar joint seen in flatfeet, skewfeet, and vertical tali. Some health care professionals use the term pronated when referring to a foot with hindfoot valgus. Forearms pronate and supinate. There is a lot more going on in foot deformities with a valgus hindfoot than can be captured with the simplistic and specific term pronated (see Basic Principle #13, this chapter).
The motions that result in those static positions should, in my opinion, be described using terms that recognize the unique and complex features of the subtalar joint. The subtalar joint differs from all other joints in the body in several ways: it is not a hinge joint or a ball-and-socket joint; its axis is not in the sagittal, coronal, or transverse plane; and it is a compound joint (several bones articulate) rather than a diarthrodial joint (two bones articulate). The subtalar joint complex is composed of 3 bones (possibly 4, if one includes the cuboid), several important ligaments, and multiple joint capsules that function together as a unit. Almost 200 years ago, Scarpa saw similarities between the hip joint and the subtalar joint complex. He coined the term acetabulum pedis, referring to a cup-like structure made up of the proximal articular surface of the navicular, the spring ligament, and the facets of the anterior end of the calcaneus (Figure 2-5).
Figure 2-3. A. Towel wrung out. B. Foot model on elastic cords wrung out in the same manner, representing a cavovarus foot with hindfoot varus and forefoot pronation. C. Towel wrung out in the opposite direction. D. Foot model wrung out in the same manner, representing a flatfoot with hindfoot valgus and forefoot supination.
He compared the femoral head to the talar head, and the pelvic acetabulum to his so-called acetabulum pedis (Figure 2-6).
I believe that the term inversion best captures the three-dimensional motions of the acetabulum pedis around the head of the talus that result in the static position “varus.” The acetabulum pedis plantar flexes (down), internally rotates (in), and supinates. Simply stated, inversion is a “down and in” movement of the acetabulum pedis around the talus. Conversely, eversion motion results in the static position “valgus.” It is a combination of dorsiflexion (up), external rotation (out), and pronation of the acetabulum pedis around the talar head. Simply stated, eversion is an “up and out” movement of the acetabulum pedis around the talus (Figure 2-7).
BASIC PRINCIPLE #7
A thorough and working knowledge of the biomechanics of the foot, and of the subtalar joint complex in particular, is mandatory for assessment and management of foot deformities in children.
The functions of the foot include provision of a stable, but supple, platform that helps it accommodate to the changing terrain below and propel the body in space. And the subtalar joint is the machinery used by the foot to adapt to the ground during the early stance phase of gait and then convert to a rigid lever during push-off. Several authors have represented the complex interrelationships between the bones of the mid- and hindfoot as a mitered hinge, but that analogy is too simplistic. Using that as a first approximation or basic concept, one must add a thorough understanding of the shape, structure, relationships, and motions of the subtalar joint complex to truly understand the biomechanics of the foot.
Figure 2-4. A. Hindfoot varus. B. Hindfoot valgus.
Figure 2-5. The acetabulum pedis, as conceptualized by Antonio Scarpa in 1818. It consists of the proximal articular surface of the navicular, the spring ligament, and the facets of the anterior end of the calcaneus.
As discussed in Basic Principle #6, Scarpa saw similarities between the hip joint and the subtalar joint complex and coined the term acetabulum pedis. Although it is not a perfect comparison, I believe that the two anatomic areas share certain features that make the comparison both valid and worthwhile. The hip, a pure ball-and-socket joint with a central point of rotation, is composed of 2 bones, 1 intra-articular ligament, and 1 joint capsule. The subtalar joint is not an independent ball-and-socket joint, though the combined motions of the subtalar joint and the immediately adjacent ankle joint give the impression of a ball-and-socket. In fact, the subtalar joint has an axis of motion in an oblique plane that is neither frontal, nor sagittal, nor coronal (Figure 2-8), thus creating motions that are best described by the terms inversion and eversion (Figure 2-7).
Figure 2-6. My concept of the comparison of the hip joint and the subtalar joint, as suggested by Scarpa. A. In the hip joint, the ball (the femoral head) rotates within the pelvic acetabulum. B. In the subtalar joint, the acetabulum pedis rotates around the ball (the talar head).
Figure 2-7. Subtalar joint motions. A and B. Inversion is plantar flexion, internal rotation, and supination of the acetabulum pedis around the talus—“down and in.” C and D. Eversion is dorsiflexion, external rotation, and pronation of the acetabulum pedis around the talus—“up and out.”
The stable structure in the hip joint is the acetabulum (the socket), while the stable structure in the subtalar joint complex is the talus (the ball). It is worth repeating that inversion comprises plantar flexion, internal rotation, and supination of the acetabulum pedis around the head of the talus—“down and in.” Eversion is a combination of dorsiflexion, external rotation, and pronation of the acetabulum pedis around the talar head—“up and out.” The static position of the inverted subtalar joint is called hindfoot varus, and the static position of the everted subtalar joint is called hindfoot valgus (Figures 2-4 and 2-7).
Figure 2-8. Axis of the subtalar joint.
The tibia and talus internally rotate during the first half of the stance phase of the gait cycle while the subtalar joint complex everts. The acetabulum pedis dorsiflexes in relation to the talus, as a component of eversion. The foot becomes quite supple, or “unlocked,” and the arch flattens. During the latter part of stance phase, the tibia and talus externally rotate while the subtalar joint complex inverts. The acetabulum pedis plantar flexes in relation to the talus, as a component of inversion, and once again supports the head of the talus. The subtalar joint and, thereby, the entire foot become rigid, or “locked” (Figure 2-9).
The foot acts as the most efficient and effective lever for the generation of power during push-off when the subtalar joint is inverted/locked and the foot is pointing directly forward, i.e., perpendicular to the transverse axis of the knee joint. This is the concept of lever arm function. Lever arm dysfunction can result from shortening the lever arm and/or weakening the triceps surae. The lever arm is shortened when the foot is externally rotated in relation to the sagittal plane of the knee. This can be due to an everted/unlocked subtalar joint and/or external tibial torsion. The force coupling (force × distance to the center of the axis of motion, i.e., length of the lever arm) can be further diminished by weakness of the triceps surae. This can occur if the triceps surae is inappropriately lengthened and, thereby, weakened (Figure 2-10).
Figure 2-9. Unlocking and locking the subtalar joint during gait. A. At heel strike, the tibia/fibula/talus internally rotate as the subtalar joint everts (“up and out”) (purple curved arrows). The acetabulum pedis dorsiflexes in relation to the talus (black arrows). The subtalar joint becomes supple, or “unlocked,” in order to accept contact with the ground as the body’s shock absorber. B. As stance phase progresses, the component parts reverse their rotation. C. At push-off, the tibia/fibula/talus are externally rotated and the subtalar joint is inverted (“down and in”), thereby plantar flexing the acetabulum pedis in relation to the talus (black arrows). The subtalar joint becomes “locked” so the foot can act as a rigid lever that is used by the triceps surae to generate power for push-off (see Figure 2-10).
The ankle joint is also composed of three bones, several important ligaments, and one joint capsule. It is a hinge joint that functions strictly in the frontal plane. The talus plantar flexes (down) and dorsiflexes (up). It is important to reiterate, and to be constantly reminded, that the subtalar joint also plantar flexes and dorsiflexes, as components of the complex movements known as inversion (“down and in”) and eversion (“up and out”).
The talonavicular and calcaneocuboid joints are also known as Chopart joints and as the transtarsal joints. The talonavicular joint is the anterior extent of the subtalar joint complex and has the largest excursion of any part of it. The calcaneocuboid joint has only a toggle of motion, and on the basis of its position within the acetabulum pedis, one could consider it to be analogous to the transverse limb of the triradiate cartilage of the acetabulum of the hip joint (Figure 2-11).
Figure 2-10. A. Lever arm deficiency. Muscles always work as part of a force-couple (force × distance to the center of the axis of motion). Therefore, the plantar flexion/knee extension (PF/KE) couple depends on the appropriate alignment and rigidity of the foot. If this is not present, the extension moment against the knee will be inadequate even with adequate strength of the triceps surae. B. The black arrow shows a long lever arm in a foot with a neutral thigh–foot angle. External rotation of the foot shortens the lever arm (distance to the center of the axis of motion—pink arrow). The external rotation can be in the subtalar joint (as a component of eversion), or it can be due to external tibial torsion, or both.
The tarsometatarsal joints are also stable joints, with little more than a toggle of motion. The keystone architecture of the 2nd metatarsal–middle cuneiform joint helps to make it so. Hypermobility of the 1st metatarsal–medial cuneiform joint can cause painful pathology.
BASIC PRINCIPLE #8
In the normal foot, the overall shape is determined by the shapes and interrelationships of the bones, coupled with the strength and flexibility of the ligaments. Muscles maintain balance, accommodate the foot to uneven terrain, protect the ligaments from unusual stresses, and propel the body forward.
Basmajian performed electromyographic assessment of the muscles of the foot and ankle and showed little or no muscular activity when physiologic loads were applied to the static plantigrade foot. Muscular activity could be demonstrated only when very heavy loads were applied to the subjects. He concluded that the height of the longitudinal arch is determined by the bone–ligament complex and that the muscles maintain balance, accommodate the foot to uneven terrain, protect the ligaments from unusual stresses, and propel the body forward. Proponents of this bone–ligament theory believe that the shape of the longitudinal arch under static loads is determined by the shapes and interrelationships of the bones, coupled with the strength and flexibility of the ligaments. Harris and Beath strongly supported this position and presented anatomic specimens to substantiate their theory. They were unable to determine whether the abnormal shapes of individual bones and joints represented a primary or secondary reflection of a long-standing flatfoot.
Figure 2-11.Considering Scarpa’s analogy of the subtalar joint (B) to the hip joint (A), the calcaneocuboid joint is comparable to the transverse limb of the triradiate cartilage. Taking the analogy even further, a calcaneonavicular tarsal coalition might also be considered a type of transverse limb of the “triradiate cartilage” of the acetabulum pedis.
Most current authors conclude that excessive ligamentous laxity is the primary abnormality in flexible flatfoot (FFF) and that bone deformities are secondary. Muscles are necessary for function and balance, but not for structural integrity. Mann and Inman confirmed that muscle activity is not required to support the arch in static weight-bearing. They also found that the intrinsic muscles are the principal stabilizers of the foot during propulsion and that greater intrinsic muscle activity is required to stabilize the transverse tarsal and subtalar joints in a flatfooted individual than in one with an average-height arch.
BASIC PRINCIPLE #9
The default position of the subtalar joint is valgus/everted (Figure 2-12).
To my knowledge, this phenomenon has not been studied, but is due, in large part, to the shape of the subtalar joint facets and the alignment of the calcaneus under the talus. The midsagittal axis of the calcaneus is lateral to the midsagittal axis of the talus and the tibia (Figure 2-13).
Figure 2-12. A. Release of the medial soft tissues in a cavovarus foot will allow the inverted subtalar joint to evert. B. In a neutrally aligned hindfoot, release of all of the ligaments around the subtalar joint will create eversion, i.e., a flatfoot. It will not invert. C. Release of the lateral soft tissues in a flatfoot will have no effect on the valgus/everted deformity.
The clinical importance and relevance of this phenomenon have to do with deformity correction surgery for cavovarus foot (varus hindfoot) and flatfoot (valgus hindfoot). Whereas medial soft tissue release is an important first step in correcting cavovarus deformity, lateral soft tissue release does nothing to correct flatfoot deformity (see Management Principles #16 and 17, Chapter 4).
BASIC PRINCIPLE #10
Valgus deformity of the hindfoot can be thought of as representing a continuum.
Here, I exclude consideration of the rigid flatfoot due to a tarsal coalition, since that is a developmental mal-deformation rather than a pure deformity. The etiologies and the natural histories of the pure valgus deformities are different, but valgus/eversion deformity of the hindfoot can be considered in relation to the severity of eversion, the flexibility of eversion, and the association with contracture of the tendo-Achilles. It ranges from mild, flexible physiologic to severe, stiff pathologic (Figure 2-14).
The natural history for the development of pain in FFF, flexible flatfoot with short Achilles (FFF-STA), and congenital vertical talus (CVT) is known. The natural history for the development of pain in congenital oblique talus (COT) has not been documented, because the very definition of the deformity is unknown. Therefore, the natural history must be assumed based on its position in the continuum of valgus deformity of the hindfoot (Figure 2-15).
Figure 2-13. CT images and plane radiographs of a foot with average normal hindfoot alignment. It happens to have both calcaneonavicular (CN) and talocalcaneal (TC) tarsal coalitions, but shows normal hindfoot alignment very well, and so is being used to make a point. A.Dorsal view 3D CT reconstruction shows normal foot alignment. B. Standing AP radiograph shows normal foot alignment. C. Standing lateral radiograph shows normal foot alignment. D. Posterior view 3D CT reconstruction shows normal hindfoot alignment. The red line represents the midsagittal axis of the talus and the tibia, i.e., the axis of gravity. The yellow line represents the midsagittal axis of the calcaneus, which is lateral to the midsagittal axis of the talus and the tibia. Therefore, the subtalar joint will evert after a plantar–medial soft tissue release (large red X). It will also frequently evert after resection of a middle facet talocalcaneal tarsal coalition (small red X) if the subtalar joint is in valgus alignment before resection. E. Coronal slice CT image confirming comments made in (D). F. Harris axial view plane radiograph confirming comments made in D.
Figure 2-14. One can reasonably consider valgus deformity of the hindfoot as a continuum. The etiologies and the natural history are different, but valgus/eversion deformity of the hindfoot ranges from the physiologic normal FFF (A) to the FFF-STA (B) to the COT (C) to the pathologic stiff CVT (D). This concept is helpful when considering the natural history of pain and dysfunction, particularly for the COT of which little is known.
BASIC PRINCIPLE #11
Cavus means hollow, empty, or excavated and is manifest in the foot by plantar flexion of the forefoot on the hindfoot. The plantar flexion may be along the medial column of the foot or across the entire midfoot. The subtalar joint may be in varus, neutral, or valgus. The ankle joint may be in plantar flexion (equinus), neutral, or dorsiflexion (calcaneus). And there may be a combination of these deformities (Figure 2-16).
Cavus deformity is shorthand for a quite varied group of deformities that share in common one feature; part or all of the forefoot is plantar flexed on the hindfoot, giving the appearance of a high arch.
BASIC PRINCIPLE #12
The foot deformity may be the primary problem or the result of the primary problem, i.e., a neuromuscular disorder. Differentiation is important (see Assessment Principle #3, Chapter 3).
Figure 2-15. The natural history for the development of pain due to valgus/eversion deformity of the hindfoot is known for all except the COT, because so little is known about that condition in general. By considering COT in this proposed deformity continuum, one can assume its natural history to be that of the development of pain.
Figure 2-16. A. Cavovarus. B. Equinocavovarus. C. Calcaneocavus (a.k.a. transtarsal cavus). D. Equinocavus. E. Calcaneocavovalgus.
The apex of the longitudinal arch generally points in the direction of the primary problem (Figure 2-17).
In a cavus foot deformity, the apex of the arch is dorsal and points toward the muscles, nerves, spine, and brain. A cavovarus foot deformity is the result of a neuromuscular disorder until proven otherwise. It is important to remember this because a treatable neuromuscular disorder, such as a tethered spinal cord or spinal tumor, is not necessarily readily apparent when a child presents with a cavovarus foot deformity. However, it should be diagnosed and treated before the foot deformity is treated. Further permanent neuromuscular deterioration should be arrested as soon as possible. In a flatfoot, the apex of the longitudinal arch is plantar, essentially pointing to the foot itself. Flatfoot is most often either a normal anatomic variant or the primary problem. Examples of the latter include FFF-STA, tarsal coalition, CVT, and skewfoot. Flatfoot can also be associated with neuromuscular disorders, such as cerebral palsy (CP), but these underlying disorders are usually apparent.
Figure 2-17. A. In a flatfoot, the apex of the longitudinal arch is plantar, essentially pointing to the foot itself. A flatfoot is either normal or, if pathologic, it is usually the primary problem. B. In a cavus foot deformity, the apex of the arch is dorsal and points toward the muscles, nerves, spine, and brain, which are usually the underlying cause of the deformity.
BASIC PRINCIPLE #13
Be accurate with terminology.
Do not use the term pronated as a substitute for the term flatfoot. There is very little pronation in a flatfoot, yet many health care professionals refer to a flatfoot as a pronated foot. It is true that pronation is one of the components of eversion of the subtalar joint, but the dorsiflexion and external rotation components are far more significant deformities. And the forefoot in a flatfoot is supinated! If it were not supinated, but instead followed the subtalar joint into eversion/“pronation,” it might be appropriate to use the term pronated. In that situation, the lateral forefoot would be elevated off the ground, a deformity that almost never exists except in some cases of congenital subtalar synostosis (see Chapter 6) (Figure 2-18).
Figure 2-18. A. Physiologic FFF. The hindfoot is in valgus alignment in relation to the tibia (green line). The forefoot is supinated in relation to the hindfoot with all metatarsal heads on the ground (black line). B. Pronated foot in a child with fibula hemimelia and congenital subtalar synostosis. There is valgus alignment of the hindfoot in relation to the tibia (green line). The forefoot (black line) is in neutral rotation (neither supinated nor pronated) in relation to the hindfoot. The entire foot is pronated in relation to the tibia with the 5th metatarsal off the ground in weight-bearing.
Another misnomer for flatfoot that is often used when discussing adult flatfoot is “dorsolateral peritalar subluxation.” It is true that eversion of the subtalar joint results in dorsal and lateral positioning of the navicular in relation to the head of the talus, i.e., peritalar. But there is no subluxation of any component part of the subtalar joint complex with even severe eversion. Subluxation means incomplete or partial dislocation of a joint, i.e., only partial contact between articular surfaces that normally have full contact. Dislocation means complete loss of contact between articular surfaces at a joint in which full contact normally exists.
Think of Scarpa’s analogy of the hip and the acetabulum pedis (see Basic Principles #6 and 7, this chapter). Dorsolateral peritalar dislocations, like hip dislocations, can occur following severe trauma. There are also congenital hip dislocations and congenital talonavicular joint dislocations, the latter found in congenital vertical talus (CVT) deformities. Congenital and developmental (cerebral palsy, myelomeningocele, Down syndrome, Charcot-Marie-Tooth) hip subluxations occur, and these are characterized by partial contact (incongruity) between the femoral head and the acetabulum. There is no analogy for that pathology in the foot. Severe eversion, which might be called dorsolateral peritalar positioning, is a rotational malalignment of the subtalar joint that is perhaps analogous to severe abduction or adduction of the hip without translational loss of contact of the articular surfaces, i.e., without subluxation.
The term flatfoot has historical precedence and, though not specific, is associated with a good visual for most people. Use it. When describing isolated dorsolateral peritalar positioning, one can use that term or the terms hindfoot valgus or hindfoot eversion.
Cavus is defined as plantar flexion of the forefoot on the hindfoot. It does not mean “high arch,” though that is the resultant effect. There may be plantar flexion of the medial column, the lateral column, or the entire forefoot on the hindfoot. The subtalar joint can be inverted, everted, or in neutral alignment. And the ankle can be plantar flexed, dorsiflexed, or in neutral alignment. When describing a cavus foot, it is best to describe all of its features. Some examples are cavovarus, equinocavovarus, calcaneocavus, and transtarsal cavus. I have seen congenital and iatrogenic calcaneo-abducto-cavo-valgus (Figure 2-16).
BASIC PRINCIPLE #14
Do not focus entirely on the foot. There is an entire child above the foot.
It is important to remember this because management of clubfoot, for example, varies depending on whether it is an idiopathic deformity or one associated with myelomeningocele or arthrogryposis. Another example is intoeing in an older child with idiopathic clubfoot, which is usually due, at least in part, to femoral anteversion. Myopic focus on the foot is dangerous (see Assessment Principles #2 and #7, Chapter 3).