Limb Alignment and Limb Length Discrepancies

Christopher A. Iobst

Raymond W. Liu

• Introduction to Pediatric Limb Deformity

Limb deformity is a frequent cause for evaluation in a young child. Parental concern regarding the appearance of the lower extremities is often encountered. This chapter focuses first on examining rotational deformities in the growing child, which are likely the most common reason for orthopedic referral. Next, coronal plane deformities, or deformities that are most apparent when viewed from the front or back, are reviewed. Finally, the evaluation and examination of limb length discrepancy (LLD) is discussed.

• Basic Normal Limb Development

Limb alignment in children changes naturally with development, particularly in the earlier years. Although these findings can be concerning to parents, many cases will spontaneously improve and only require reassurance. In other circumstances, such as substantial genu varum (bowlegs), more careful observation and treatment may be necessary.

Foot progression angle (FPA) is the angle between the long axis of the foot and the direction of gait (Figure 15.1). A slightly externally rotated FPA at maturity is normal, with only a small amount of change with development. An internally rotated FPA is often observed in younger children. In infants who have not begun to walk, the most common cause of in-toeing is metatarsus adductus. This can be confirmed by finding a curved lateral border to the foot on examination. In children who are noted to have in-toeing as they begin to walk (usually at 1 year of age), the most common cause is internal tibial torsion. In children older than 4 or 5 years of age, the most common cause of in-toeing is usually excessive femoral anteversion. Femoral anteversion is defined as an anterior rotation (in the transverse plane) of the proximal femur relative to the distal femur and knee. At birth, the average proximal femur is rotated 30° to 35° anteriorly, and with time, this decreases to 15° to 20° by skeletal maturity. Anteversion is a physical characteristic such as height; all humans have height, some are taller than others. Similarly, all normal humans have anteversion; yet some are born with a lot more anteversion (excessive) than the average values above. In these subjects, the neonatal external hip flexion contractures mask the effect of underlying femoral anteversion for the first years of life. However, as these external hip contractures gradually begin to disappear, the child with excessive femoral anteversion becomes more apparent. Neurological disorders can affect the ability of the femur to change its anteversion. For instance, patients with hemiplegia will have more internal rotation of the affected femur with persistent fetal anteversion which has not remodeled, presumably as a consequence of altered neuromuscular control.

When viewed from the front (coronal plane), children are generally born with genu varum or bowleggedness. This typically decreases until the age of 2 years when children begin to develop genu valgum. The valgus increases until around the age of 4 years and then gradually settles into its adult alignment of slight residual valgus by the age of 7 years.¹

LLD is an inequality of the length of the extremities, most commonly referring to the lower extremities. It is common to see LLD in the general population, as the mean LLD has been found to be
approximately 5 mm with a standard deviation of 4 mm.² In most cases, LLD increases proportionally with the child’s overall limb growth. It is useful to know that boys reach half of their ultimate lower extremity lengths at 4 years of age, while girls do so at 3 years of age.³ Thus, if one does diagnose LLD at these ages, it would be expected to double at skeletal maturity, while predictions at other ages can be quickly done with the multiplier method, where the discrepancy is factored by a multiplier based on the child’s gender and age.³

FIGURE 15.1 The foot progression angle (FPA) is the angle between the direction of gait and the direction of the foot. These images demonstrate (A) internal, (B) neutral, and (C) external FPA.

• In-toeing

Introduction

In-toeing is a common finding, particularly in growing children. The most common causes of in-toeing are metatarsus adductus, internal tibial torsion, and excessive femoral anteversion. Metatarsus adductus is a deformity at the level of the midfoot and is first diagnosed in newborns. Internal tibial torsion is an inward twisting of the tibia and is commonly diagnosed in children shortly after walking. Excessive femoral anteversion is an inward twisting of the femur and is commonly diagnosed after 4 to 5 years of age.

Clinical Significance and Natural History

In most cases, the diagnosis can be established by a careful physical examination, and the treatment is reassurance and observation as needed. Less commonly, children with significant metatarsus adductus can have foot pain or difficulty with shoe wear. Patients with internal tibial torsion and femoral anteversion can have difficulties with excessive tripping and/or persistent lower extremity pain with activities. By 10 years of age, most children will have reached their final adult rotational alignment. No substantial correction of rotation is expected to occur with growth after this age. In regard to the natural history of in-toeing, an osteological study found no association between femoral and tibial rotation and arthritis of the spine, hips, and knees, which provides reassurance to families concerned about in-toeing.⁴ It is important to note that this study focused on a general population and thus should be used for reassurance in asymptomatic cases, rather than in cases with severe deformity, comorbidities such as cerebral palsy, or in children with significant symptoms.⁴

History and Physical Examination

The age at which the in-toeing was first noticed is an important component of the history. As noted above, in-toeing noticed in an infant suggests a foot origin, in-toeing with initial walking suggests tibial torsion, and later in-toeing is more likely secondary to excessive internal rotation in the femur. Prematurity and delayed onset of walking of 18 months or later should lead the clinician to suspect developmental delays such as that seen in mild cerebral palsy. Although asymmetric in-toeing is frequently reported by family members, the physical examination usually demonstrates symmetric rotation. In those cases, the asymmetry is simply due to the immature gait. If true asymmetry is noted, then neurologic conditions such as hemiplegia should be suspected. Changes in the in-toeing with growth are often noted by the family, and tripping while running is a common complaint of families. Pain is uncommonly reported in younger children, but knee pain may be reported in adolescents with excessive femoral anteversion.

Observational gait analysis is important for all of the clinical conditions in this chapter. Oftentimes, you will get a more natural gait pattern if you can observe the child before they reach the clinic room and before they become aware they are the center of attention. When performing a gait analysis, it is important the child is barefoot and the legs are fully exposed and you have a good distance (private hallway is ideal) from which to observe from the front and the side. This allows enough room for observing multiple gait cycles (

Video 15.1). During observational gait analysis, it is important to look at each aspect of the gait individually and then observing the gait as a whole package. It is critical to focus on each segment of the lower body individually (foot/ankle, knee, and hip) in both the frontal and sagittal planes. After assessing each level, the following questions should be pondered while watching the child walk: Is there any limping? Is there a full, smooth range of motion at each of the joints, or does the gait appear stiff at a particular level? Are there any compensatory maneuvers such as toe walking, vaulting, circumduction, or knee flexion? Is there any joint instability or thrust with gait? Are the legs straight or is there an associated angular deformity present? Is the FPA straight or rotated? For a more detailed description, please see Chapter 4 on Gait Analysis.

With in-toeing, the clinician will observe an internal FPA, in which the direction of the foot is rotated internally relative to the direction of the child’s overall gait (Figure 15.1). Many children will self-correct their gait when observed. Asking a child to walk fast or run is usually enough of a distraction to get them to revert to their baseline gait pattern. It is also very useful to observe the child when he/she is first walking into the clinic and not aware that he/she is being observed.

The key portion of the physical examination involves a series of maneuvers in the prone position called the “rotational profile.” Femoral rotation, tibial torsion, and foot alignment of each limb are assessed in the rotational profile. The foot can be examined for metatarsus adductus by determining that the lateral border of the foot is not straight but convex. The degree of deformity can be assessed with the heel bisector line which is an imaginary line drawn that bisects the heel, and the physician observes which toe this line passes through (Figure 15.2). In a normal foot, the heel bisector line passes between the second and third toes, while in a foot with metatarsus adductus the line is lateral to this. If the foot has metatarsus adductus, it is appropriate to determine if the adductus is flexible or fixed by trying to correct the position of the foot. If the foot can be corrected to a normal position where the lateral border of the foot is straight, observation is generally the only treatment necessary.

Internal tibia torsion is most commonly assessed by measuring the thigh foot angle in the prone position with the knee flexed to 90°. The angle between the thigh and the axis of the foot represents the thigh foot angle (

Video 15.2). Generally, this is between neutral and 10° externally rotated. It is important to allow the foot to naturally dorsiflex to neutral. The clinician should be careful to avoid accidently manipulating the foot into a rotated position which leads to an inaccurate thigh foot angle. If the clinician is unsure about the true proper movement of the foot, or if there is foot deformity, then the thigh malleolar axis can be utilized. In this measurement, a line perpendicular to a line passing between the medial and lateral malleoli is used as the second line to compare to the axis of the thigh (Figure 15.3). Thigh malleolar axis is approximately 20° greater than thigh foot angle, and so the normal range is approximately 20° to 30° externally rotated.

FIGURE 15.2 The heel bisector line is the intersection between a line bisecting the hindfoot and the toes. Normally, this line should pass through the webspace between the second and third toes. In this child with metatarsus adductus, the line is more lateral, intersecting the webspace between the fourth and fifth toes.

Children with excessive femoral anteversion may be able to substantially internally rotate their feet in stance (Figure 15.4). Children with excessive femoral anteversion can be easily placed into a W-sitting position due to their increased hip internal rotation (Figure 15.5).

In general, each child will have about 90° of total hip rotation; excessive femoral anteversion is assessed by comparing internal and external rotation of the hip with the hip in extension. In the case of a very nervous toddler, internal rotation can be assessed with the knees bent over the side of the table while the child is lying on their back next to their parent. For less anxious children, hip motion is best assessed with the child in a prone position, keeping the pelvis level on the examination table. Hip internal rotation is measured with the feet rotated away from each other, while hip external rotation is measured with the feet rotated toward each other, flexing the knees such that the tibia tends to cross (

Video 15.3). It is important that the knees are kept together, particularly in external hip rotation. Allowing the knees to separate from each other will result in measuring a falsely higher external rotation angle. Generally, a child with 75° of hip internal rotation and significantly less external rotation (15°) is defined as having excessive femoral anteversion. However, any substantial mismatch with more internal than external rotation could contribute to a negative FPA and in-toeing.

FIGURE 15.3 Both thigh foot angle (TFA) and thigh malleolar axis (TMA) can be used to evaluate tibial torsion. In both cases, the child is prone and the knee is flexed 90°. The blue line represents the axis of the thigh. A, For TFA, the foot is dorsiflexed to neutral and the red lines represents the foot axis. The TFA is the angle (yellow) between the thigh and foot. B, For TMA, a line connecting the medial and lateral malleoli is determined (dotted red line). The TMA is the angle (yellow) between a line orthogonal to this (solid red line) and the thigh axis.

FIGURE 15.4 This child with excessive femoral anteversion can substantially internally rotate both hips and bring the feet nearly 180° to each other.

Pitfalls in Diagnosis

In diagnosing metatarsus adductus, it is important to be sure that the child does not have a clubfoot, as metatarsus adductus is one of the components of a clubfoot. If the child has good dorsiflexion range of motion in the ankle, then the diagnosis of clubfoot is unlikely. It is important to make sure the foot is angulated in the inward direction, as a foot in the opposite direction would likely be a calcaneovalgus foot in an infant.

Internal tibial torsion can be difficult to diagnose in a child with foot deformity. As described above, in concomitant cases of foot deformity, it is preferable to use thigh malleolar axis. Because proper dorsiflexion of the foot can be difficult to position, it is reasonable to check thigh malleolar axis whenever examining thigh foot angle and evaluating the child more carefully if the thigh malleolar axis is not 20° more externally rotated than the thigh foot angle as expected. Internal tibial torsion can also masquerade as genu varum, or the two conditions can occur in tandem. See below including a description of the “cover-up test” to differentiate between the two.

Excessive femoral anteversion is generally fairly straightforward to diagnose by comparing hip internal rotation with hip external rotation. The main pitfall is that in patients with excessive femoral anteversion, concurrent internal or external tibial torsion can be overlooked. With combined femoral anteversion and internal tibial torsion, the child can have a large negative FPA. With combined femoral anteversion and external tibial torsion, the two deformities compensate for each other with a fairly neutral FPA. However, this combination (also known as miserable malalignment) tends to place more stress on the patellofemoral joint, and knee pain can occur, particularly in older children in the adolescent age range.

FIGURE 15.5 It is common for children with excessive femoral anteversion to sit in a W-position, with the hips internally rotated. This sitting position should be discouraged, as it is thought to prevent proper remodeling of the femur with growth.

Differential Diagnosis

Subtle cerebral palsy can present with asymmetric in-toeing. Although parents may notice more in-toeing on one side than the other in children with routine femoral anteversion or internal tibial torsion, it is important to be sure that the child does not have spastic hemiplegia. In cerebral palsy, the child generally exhibits increased tone when the extremities are manipulated for examination. Also, irregularities when walking in the hallway can be helpful
and particularly obvious with the child running, which can produce posturing of the upper extremity (see Chapter 4 on Gait Analysis).

Diagnostic Tests or Advanced Imaging

Rotational deformities are mostly diagnosed and managed without imaging. Femoral anteversion and tibia torsion are not readily apparent on plain radiographs, although subtle signs such as apparent coxa valga (a neck shaft angle greater than 145 degrees) can be seen with excessive femoral anteversion. In metatarsus adductus, an anteroposterior (AP) view of the foot will confirm and quantify the adductus deformity, although this is not necessary for diagnosis.

Advanced imaging such as computed tomography (CT) and magnetic resonance imaging (MRI) can be used to quantify the magnitude of femoral anteversion and tibia torsion. However, this is generally unnecessary for diagnostic purposes and is mainly considered as a presurgical test.

Treatment

In most cases, the causes of in-toeing can be treated with observation. Metatarsus adductus generally improves with observation. Metatarsus adductus that cannot correct past neutral can be treated with serial casting. On occasion, surgery is recommended to correct the foot if the deformity has persisted into childhood and is symptomatic.

Since many parents are frustrated by their child’s gait and assume that there must be something wrong, they can be dissatisfied with the answer from the physician that no treatment is necessary. It is controversial whether it is wise to advice against W-sitting. On one hand, there are no data to suggest it makes a difference, and most parents are wise to pick their battles carefully. Others may advocate this approach as a way to placate families who feel that they must do something and will provide the parents with something to monitor their child and often appease their need to have something done (Figure 15.5). Bracing has not been shown to be effective and is not used for these conditions. Excessive femoral anteversion and external tibial torsion are also largely treated with observation. In older children with persistent symptoms of the above miserable malalignment, physical therapy might be utilized to help the child strengthen and compensate for the deformity. Surgical reconstruction for patella femoral pain as a result of “miserable malalignment” can be recommended for children with persistent deformity and/or persistent pain recalcitrant to normal conservative measures.

When to Refer

As noted above, most children with in-toeing can be treated with reassurance to the parents that it should improve spontaneously. Some families may be unsatisfied with observation as the only form of treatment because older family members may have worn braces or special shoes for similar conditions in the past. A child with metatarsus adductus that is not correctable to a neutral position or a walking child having difficulties with shoe wear or foot pain should be referred. Internal tibia torsion or excessive femoral anteversion with persistent symptoms, such as excessive falling or pain that limits activity, should also be referred. For children with substantial residual rotation after the age of 8 years, a referral to a pediatric orthopedic surgeon is reasonable to educate families and to discuss treatment options.

• Out-toeing

Introduction

Out-toeing is less common than in-toeing, particularly at younger ages. It is normal to have a slightly externally rotated FPA by adulthood. Out-toeing in infants generally originates from an external hip rotation contracture due to intrauterine positioning, which generally starts to improve by 18 months of age as they learn to walk. Out-toeing in walking children commonly originates from external tibial torsion or in children with excessively flat feet.

Clinical Significance and Natural History

Most cases of out-toeing can simply be observed. External rotation hip contractures generally resolve on their own as the child continues to walk. External tibial torsion tends to persist but is generally asymptomatic. Sometimes children will report pain, generally in the later juvenile or adolescent age ranges, with pain from external tibial torsion potentially affecting the knee, shin, ankle, or foot. An osteological study did not find any association between external tibial torsion and arthritis of the spine, hips, or knees.⁵

History and Physical Examination

Children who have just begun to walk and have out-toeing generally have external hip rotation contractures. Children who have been out-toeing since walking age are more likely to have external tibial torsion. One should particularly suspect other etiologies with unilateral out-toeing, as physiologic out-toeing is commonly bilateral with external tibial torsion. It is useful to determine if there is any history of breech delivery, increasing suspicion for potential hip dysplasia. On the other hand, children who begin to out-toe in the juvenile and early adolescent age ranges may have other pathologies such as Legg-Calve-Perthes disease or slipped capital femoral epiphysis (SCFE).

As with in-toeing, it is important to perform observational gait analysis as described above (

Video 15.4). Children with out-toeing will have an external FPA (Figure 15.1). External rotation contracture of the hip generally occurs in infants and young toddlers and can be examined in the supine position, with substantially more external hip rotation than internal hip rotation (

Video 15.5). External tibial torsion can be diagnosed based on the thigh foot angle, as described above (

Video 15.2). Again, it is useful to concurrently assess the thigh malleolar axis (Figure 15.3) to avoid being deceived by the foot position. This is particularly important in the case of flatfoot, where midfoot collapse and an abduction deformity of the midfoot can lead to the false diagnosis of external tibial torsion.

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