Torsional and Angular Deformities

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Chapter 667 Torsional and Angular Deformities

667.1 Normal Limb Development

An understanding of normal limb development is essential for pediatricians to recognize pathologic conditions during routine and targeted exams. During the 7th wk of intrauterine life, the lower limb rotates medially to bring the great toe toward the midline. The hip joint forms by the 11th wk; the proximal femur and acetabulum continue to develop until physeal closure in adolescence. At birth, the femoral neck is rotated forward approximately 40 degrees. This forward rotation is referred to as anteversion (the angle between the axis of the femoral neck and the transcondylar axis). The increased anteversion increases the internal rotation of the hip. Femoral anteversion decreases to 15-20 degrees by 8-10 yr of age. The second source of limb rotation is found in the tibia. Infants can have 30 degrees of medial rotation of the tibia, and by maturity the rotation is between 5 degrees of medial rotation and 15 degrees of lateral rotation (Fig. 667-1). Excessive medial rotation of tibia is referred to as medial tibial torsion. The tibial torsion is the angular difference between the axis of the knee and the transmalleolar axis. The medial or lateral rotation beyond ±2 standard deviations (SDs) from the mean is considered abnormal rotation.

Limb rotation is also found in the foot. The abnormalities could be excessive adduction or abduction. Torsional deformity may be simple, involving a single segment, or complex, involving multiple segments. Complex deformities may be additive (internal tibial torsion and internal femoral torsion are additive) or compensatory (external tibial torsion and internal femoral torsion are compensatory).

The normal tibiofemoral angle at birth is 10-15 degrees of physiologic varus. The alignment changes to 0 degrees by 18 mo, and physiologic valgus up to 12 degrees is reached in between 3 and 4 yr of age. The normal valgus of 7 degrees is achieved by 5-8 yr of age (Fig. 667-2). Persistence of varus beyond 2 yr of age may be pathologic. Overall, 95% of developmental physiologic genu varum and genu valgum cases resolve with growth. Persistent genu valgum or valgus into adolescence is considered pathologic and deserves further evaluation.

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Figure 667-2 The normal coronal alignment of the knee plotted for age.

(From Salenius P, Vanka E: The development of the tibiofemoral angle in children. J Bone Joint Surg Am 57:259–261, 1975.)

667.2 Evaluation

In evaluation of concerns relating to the limb, the pediatrician should obtain a history of the onset, progression, functional limitations, previous treatment, evidence of neuromuscular disorder, and any significant family history.

The examination should assess the exact torsional profile and include (1) foot progression angle, (2) femoral anteversion, (3) tibial version with thigh-foot angle, and (4) assessment of foot adduction and abduction.

Foot Progression Angle

Limb position during gait is expressed as the foot progression angle (FPA) and represents the angular difference between the axis of the foot with the direction in which the child is walking. Its value is usually estimated by asking the child to walk in the clinic hallway (Fig. 667-3). Inward rotation of the foot is assigned a negative value, and outward rotation is designated with positive value. The normal FPA in children and adolescents is 10 degrees (range, −3 to 20 degrees). The FPA serves only to define whether there is an in-toeing or out-toeing gait.

Femoral Anteversion

Measuring the hip rotation with the child in prone position, the hip in neutral flexion or extension, thighs together, and the knees flexed 90 degrees indirectly assesses the anteversion (Fig. 667-4). Both hips are assessed at the same time. As the lower leg is rotated ipsilaterally, this produces internal rotation of the hip, whereas contralateral rotation produces external rotation. Excessive anteversion increases internal rotation, and, retroversion increases the external rotation.

Tibial Rotation

Tibial rotation is measured using the transmalleolar angle (TMA). The TMA is the angle between the longitudinal axis of the thigh with a line perpendicular to the axis of the medial and lateral malleolus (Fig. 667-5). In the absence of foot deformity, the thigh foot angle (TFA) is preferred (Fig. 667-6). It is measured with the child lying prone. The angle is formed between the longitudinal axis of the thigh and the longitudinal axis of the foot. It measures the tibial and hindfoot rotational status. Inward rotation is assigned a negative value, and outward rotation is designated a positive value. Inward rotation indicates internal tibial torsion, whereas outward rotation represents external tibial torsion. Infants have a mean angle of −5 degrees (range, −35 to 40 degrees) as a consequence of normal in utero position. In mid-childhood through adult life, the mean TFA is 10 degrees (range, −5 to 30 degrees).

667.3 Torsional Deformities

Metatarsus Adductus

Metatarsus adductus (Chapter 666.01) manifests with forefoot adduction and inversion of all metatarsals. Ten to 15% are associated with hip dysplasia. The prognosis is good, because the majority get better with nonoperative intervention. The feet, which are flexible and correctable up to neutral, are treated with stretching exercises. Those that are not completely correctable are treated with serial casting. Rigid deformities, which are not correctable by stretching, are treated with medial capsulotomy of the 1st metatarsal cuneiform joint and soft-tissue release by 2 yr of age. Osteotomies of the base of the metatarsal are usually done after 6 yr of age.

667.4 Coronal Plane Deformities

Genu varum and genu valgum are common pediatric deformities of the knee. The age-appropriate normal values for knee angle are presented in Figure 667-2. Tibial bowing is common during the 1st year, bowlegs are common during the 2nd year, and knock-knees are most prominent between 3 and 4 yr of age.

Genu Varum

Physiologic bowleg is a common torsional combination that is secondary to normal in utero positioning (Fig. 667-8). Spontaneous resolution with normal growth and development can be anticipated. Persistence of varus beyond 2 yr of age may be pathologic. The different causes are metabolic bone disease (vitamin D deficiency, rickets, hypophosphatasia), asymmetric growth arrest (trauma, infection, tumor, Blount), bone dysplasia (dwarfism, metaphyseal dysplasia), and congenital and neuromuscular disorders (Table 667-1). It is prudent to differentiate physiologic bowing from Blount disease (Table 667-2). Physiologic bowing should also be differentiated from rickets and skeletal dysplasia. Rickets has classic bone changes with trumpeting widening and fraying of the metaphysis and widening of the physis (Chapter 48).

Table 667-1 CLASSIFICATION OF GENU VARUM (BOWLEGS)

PHYSIOLOGIC

ASYMMETRIC GROWTH

METABOLIC DISORDERS

SKELETAL DYSPLASIA

Modified from Thompson GH: Angular deformities of the lower extremities. In Chapman MW, editor: Operative orthopedics, ed 2, Philadelphia, 1993, JB Lippincott, pp 3131–3164.

Table 667-2 DIFFERENTIATION OF LEG BOWING

PHYSIOLOGIC BOWING BLOUNT DISEASE
Gentle and symmetric deformity Asymmetric, abrupt, and sharp angulation
Metaphyseal-diaphyseal angle <11 degrees Metaphyseal-diaphyseal angle >11 degrees
Normal appearance of the proximal tibial growth plate Medial sloping of the epiphysis
Widening of the physis
Fragmentation of the metaphysis
No significant lateral thrust Significant lateral thrust

Tibia Vara

Idiopathic tibia vara, or Blount disease, is a developmental deformity resulting from abnormal endochondral ossification of the medial aspect of the proximal tibial physis leading to varus angulation and medial rotation of the tibia (Fig. 667-9). The incidence is greater in African-Americans and in toddlers who are overweight, have an affected family member, or started walking early in life. It has been classified into three types depending on the age at onset: infantile (1-3 yr), juvenile (4-10 yr), and adolescent (11 yr or older). The juvenile and adolescent forms are commonly combined as late-onset tibia vara. The exact cause of tibia vara remains unknown.

The infantile form of tibia vara is the most common; its characteristics include predominance in black girls, approximately 80% bilateral involvement, a prominent medial metaphyseal beak, internal tibial torsion, and leg-length discrepancy (LLD). The characteristics of the juvenile and adolescent forms (late onset) include predominance in black boys, normal or greater than normal height, approximately 50% bilateral involvement, slowly progressive genu varum deformity, pain rather than deformity as the primary initial complaint, no palpable proximal medial metaphyseal beak, minimal internal tibial torsion, mild medial collateral ligament laxity, and mild lower extremity length discrepancy. The infantile group has the greatest potential for progression.

An anteroposterior standing radiograph of both lower extremities with patellas facing forward and a lateral radiograph of the involved extremity should be obtained (Fig. 667-10). Weight-bearing radiographs are preferred and allow maximal presentation of the clinical deformity. The metaphyseal-diaphyseal angle can be measured and is useful in distinguishing between physiologic genu varum and early tibia vara (Fig. 667-11). Langenskiöld has six stages on radiographs (Fig. 667-12). The differentiation is based on fragmentation of the epiphysis, beaking of the medial tibial epiphysis, depression of the medial tibial plateau, and formation of a bony bar. Occasionally, CT with three-dimensional reconstructions, or MRI, may be necessary to assess the meniscus, the articular surface of the proximal tibia including the posteromedial slope, or the integrity of the proximal tibial physis.

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Figure 667-12 Depiction of the stages of infantile Blount disease.

(From Langeskiöld A: Tibia vara [osteochondrosis deformans tibiae]: a survey of 23 cases, Acta Chir Scand 103:1, 1952.)

Management is based on the stage of the disease, the age of the child, and nature of presentation (primary or recurrent deformity). In children younger than 3 yr and Langenskiöld stage <3, bracing is effective and can prevent progression in 50% of these children. A maximal trial of 1 yr of orthotic management is recommended. If complete correction is not obtained after 1 yr or if progression occurs during this time, a corrective osteotomy may be indicated. Surgical treatment is also indicated in children >4 yr of age, those at Langenskiöld stage >3, and those with severe deformities. A proximal tibial valgus osteotomy and associated fibular diaphyseal osteotomy are usually the procedures of choice. In late-onset tibia vara, correction is also necessary to restore the mechanical axis of the knee. Hemiplateau elevation with correction of posteromedial slope has also been established as a treatment modality in relapsed cases.

667.5 Congenital Angular Deformities of the Tibia and Fibula