Pediatric lower extremity anomalies represent a diverse set of conditions, ranging from normal musculoskeletal development and physiologic variations to severe limb deficiencies. These may occur in isolation or be part of a more global condition. Understanding age-appropriate development and normal musculoskeletal growth is essential to proper diagnosis. A thoughtful evaluation and a patient-centered approach are critical to optimizing health-related quality of life while minimizing the cost, burden, and morbidity of management.

The internal or external positioning of the foot during gait (intoeing or out-toeing) or the foot progression angle is the summation of the torsional contributions from the lower extremity segments (femur, tibia, and foot). Deviations in foot progression are a frequent source of caregiver anxiety and reason for referral. Determining normal versus pathologic rotational abnormalities is dependent on the child’s age at the time of evaluation as norms change throughout skeletal growth.

Femoral version refers to the angle of the femoral neck relative to the transcondylar axis of the distal femur. Femoral version can be inferred clinically by assessing hip range of motion with the patient prone and the pelvis level. A hip arc of motion skewed toward internal rotation relative to external rotation suggests a greater degree of anteversion. Femoral anteversion averages approximately 40° at birth and typically decreases to an average of 10° to 15° by 8 to 10 years of age.¹

Tibial torsion is defined as the rotational relationship between the proximal and distal articular axes of the tibia around its longitudinal axis. Tibial torsion is typically quantified on physical examination by measuring a patient’s thigh-foot angle while prone with the knee flexed 90°. Using this technique, tibial torsion averages approximately 5° internal at birth, changing to approximately 10° external by 8 years of age.²

Evaluation of a perceived rotational abnormality in a child should begin with a thorough history and
physical examination. It is important to elucidate the perceived influence of the rotational abnormality on the patient’s functional status with respect to pain, balance, and function. Functional difficulties such as frequent tripping should be understood with knowledge of a typical evolution of gait. A gradual deterioration in gait over time should alert the provider to the possibility of an underlying neuromuscular condition.

Physical examination of a perceived rotational abnormality should include evaluation of the patient’s rotational profile.² This includes measuring the patient’s internal rotation and external rotation of the hip, thigh-foot angle, heel-bisector angle, and foot progression angle during gait. A neutral foot progression angle does not exclude the presence of abnormalities in multiple segments. For example, the combination of external tibial torsion with excessive femoral anteversion would result in a neutral foot progression angle but can place increased stress at the patellofemoral joint and has been termed miserable malalignment syndrome.

Radiographs are not typically required for assessment of torsional profile. CT has historically been used to quantify pathologic femoral version and tibial torsion. However, CT exposes the child to significant radiation exposure. To avoid this exposure, some institutions have switched to MRI in patients who can tolerate the procedure without sedation. In the future, EOS imaging technology may become more common for radiographic rotational profiles.³

Because most rotational abnormalities in young children improve with growth, reassurance and observation are the mainstays of management. Further, in the general adult population, persistent abnormalities in torsional profile, such as increased femoral anteversion or tibial torsion, have not been associated with long-term conditions such as osteoarthritis of the knee or hip.⁴ The parents should be counseled that nonsurgical management of benign childhood torsional abnormalities (eg, physical therapy or orthoses) has not been shown to be effective and may be associated with adverse psychological effects.

Surgical management of torsional abnormalities in otherwise healthy children can be considered for functional issues or severe cosmetic abnormalities deemed unacceptable to patients and their families in children older than 10 years. Abnormal femoral version and tibial torsion may require treatment in older patients who present with hip and/or knee pain, patellofemoral dysfunction, or deviations of gait pattern. Abnormal femoral version has been cited as contributing to symptomatic femoroacetabular impingement.⁵ Femoral anteversion is also known to exacerbate hip dysplasia. Abnormal tibial torsion negatively affects muscle lever arms and force production during gait. In patients with neuromuscular conditions, such as spina bifida and cerebral palsy, abnormal torsion can negatively affect the ability to ambulate.

Surgical management of tibial torsion generally consists of a supramalleolar osteotomy unless there is additional deformity, whereas surgical management of femoral rotational abnormalities can be considered through a variety of approaches, generally proximally or distally if there is associated proximal coronal or sagittal plane deformity at the same region, versus proximally, distally, or midshaft if there is not associated deformity.

An understanding of the normal coronal or frontal plane lower extremity development is critical in differentiating normal variations from pathologic conditions. Infants are born with mild genu varum (approximately 10° to 15° of varus). This typically decreases to neutral tibial-femoral alignment by 18 to 24 months of age and progresses to genu valgum thereafter. Knee valgus reaches a maximum at approximately 3 years of age (10° to 15° of valgus), after which knee valgus generally decreases to adult norms (approximately 7° to 8°) by age 6 years.⁶ Further changes in coronal plane knee alignment are uncommon in late childhood or adolescence in the absence of physeal disturbance.

Evaluation of coronal plane abnormalities of the knee begins with a detailed history and physical examination. History should focus on the perceived change in alignment with growth, underlying medical conditions, nutrition (eg, vitamin D deficiency in babies who are breastfed exclusively), and potential prior insults to the physis (eg, trauma or infection). Physical examination should be performed with the patient non-weight bearing and in both static and dynamic weight bearing if possible. The patient’s growth and stature should be scrutinized for any evidence of skeletal dysplasia. It is important to assess for the presence of concomitant rotational and/or sagittal plane abnormalities, ligamentous laxity, and leg-length discrepancy.

When pathologic coronal plane variations are suspected, radiographic evaluation should include full-length lower extremity radiographs with the patient standing (if possible). Imaging is obtained with the patella facing forward to minimize distortion caused by rotational abnormalities. Radiographs allow the provider to evaluate mechanical axis deviation (MAD), location of deformity, physeal disturbance,
and limb-length discrepancy. Any identified deformity should also undergo imaging in an orthogonal plane to look for potential sagittal plane deformity.

The mechanical axis of the limb is measured with a line connecting the center points of the hip and ankle, with the normal range from 1 to 15 mm relative to the center of the joint and the ideal being 0 ± 3 mm. Medial MAD greater than 15 mm is considered varus and any lateral MAD is considered valgus. The knee can also be categorized into zones to help describe the degree of deformity (Figure 1).

Surgical techniques to correct valgus and varus deformities are similar. Growth modulation can be performed for functional physes with sufficient growth remaining with either tension band plating or transphyseal screws.⁷ In patients presenting closer to skeletal maturity, osteotomy with acute or gradual correction may be indicated.

Genu valgum is considered physiologic until age 8 years. Persistence of moderate to severe valgus past this age is pathologic and may be idiopathic in nature or may be secondary to metabolic disorders, skeletal dysplasias, congenital limb deficiency associated with hypoplasia of the lateral femoral condyle, or injury to the lateral femoral and/or tibial physes.

A 2019 study has demonstrated that although Cozen phenomenon does occur in metaphyseal proximal tibial fractures, patients are at low risk of having persistent clinically significant genu valgum and therefore do not all need regular clinical follow-up or radiographic screening. Patients with an initial valgus deformity of greater than 4° with an ipsilateral fibular fracture or with a medial metaphyseal gap are at a higher risk of the development of deformity and should be followed more closely.⁸

Nonsurgical modalities such as orthoses or physical therapy have not been demonstrated to change the natural history of genu valgum. Typical indications for surgical intervention include a clinically unacceptable deformity and/or lateral deviation of the mechanical axis lateral to the tibial plateau. Surgical intervention with mild MAD (zone 2) can also be considered but is mainly an aesthetic indication because there is no evidence of increased risk of future arthritis.⁹ For patients with this degree of deformity, treatment should be deferred unless it is paired with pain or functional issues.

Surgical options for pathologic genu valgum include medial hemiepiphysiodesis (temporary or permanent) or acute osteotomy, with careful attention paid to any stretching of the peroneal nerve with acute correction. Goals of surgical management for pathologic genu valgum include restoration of a normal mechanical axis and joint orientation while minimizing complications. Guided growth is dependent on sufficient growth potential of the lateral-side physes to correct deformity with time. Therefore, it is not a reliable option for patients who are at (or near) skeletal maturity or in patients with pathologic lateral physes.

Genu varum is considered normal until age 2 years. Physiologic genu varum frequently demonstrates gradual bowing in the distal femur and proximal tibia without physeal abnormalities on radiographs and often resolves spontaneously with growth. Therefore, observation and reassurance are recommended.¹⁰ Persistence of genu varum beyond age 2 years is abnormal and warrants further evaluation.⁷ Etiologies of pediatric pathologic genu varum include metabolic bone diseases, skeletal dysplasias, and physeal growth disturbances.

Idiopathic tibia vara (Blount disease) is characterized by an abrupt varus deformity at the proximal tibia. Although defined primarily based on the coronal plane deformity, Blount disease is frequently associated with internal rotation and flexion of the proximal tibia. The specific etiology of Blount disease is unknown, but it is thought to be related to deceleration of growth in
the posteromedial proximal tibial physis secondary to genetic predisposition, obesity, early walking, and other nutritional factors. Left untreated, Blount disease is associated with progressive coronal deformity, leg-length discrepancy (in unilateral cases), gait abnormality, and premature arthritis.

Blount disease is classified based on the age of onset; two forms are most common: infantile (onset before age 5 years) and adolescent (onset after age 10 years). A third form, juvenile, has been described for patients aged 5 to 10 years at diagnosis with intermediate findings.

Infantile Blount disease is bilateral in approximately 50% of patients. Imaging findings of infantile Blount disease include physeal changes and medial metaphyseal beaking. The metaphyseal-diaphyseal angle, defined as the angle between the proximal tibial metaphysis and a line perpendicular to the long axis of the tibial diaphysis, can help distinguish between physiologic and pathologic genu valgum¹¹ (Figure 2). An angle of up to 9° is associated with a 95% chance of spontaneous resolution, whereas angles of 9° or greater have a 95% likelihood of pathologic and progressive tibia vara.¹² Infantile Blount disease has historically been classified according to the Langenskiöld classification.¹³ A modified classification that correlates extreme sloping of the medial metaphyseal defect to a poor prognosis has been proposed in a 2019 study.¹⁴

Orthotic management with the goal of unloading the medial tibial physis can be considered for a young patient (age 3 years or younger), although the evidence for this is poor. For children older than 3 years and with progressive deformity, surgical intervention is recommended. Surgical options include growth modulation and/or physeal bar resection if there is skeletal growth remaining. In patients with little growth remaining, proximal tibial osteotomy with or without a midshaft fibular osteotomy is used for acute versus gradual deformity correction.

Adolescent Blount disease typically is less severe than infantile forms and is more often unilateral. Adolescent Blount disease may be associated with varus deformities of the distal femur and/or valgus deformities of the distal tibia. Recognition and concomitant management of these deformities are important to successful outcomes. Adolescent Blount disease is strongly associated with obesity and has been associated with increased rates of hypertension and obstructive sleep apnea.¹⁵,¹⁶ Because of the limited growth potential and a frequent association of obesity, nonsurgical management has no role in the management of adolescent Blount disease. Surgical options include growth modulation or a proximal tibial osteotomy with either acute or gradual correction. Skeletal age is frequently advanced in patients with adolescent Blount disease, so bone age should be assessed before attempted guided growth.

Congenital limb deficiencies are rare conditions that are challenging to treat. Treatment of these patients is best done using a multidisciplinary approach with the goal
of creating a functional lower extremity for the patient. Care should be taken to minimize physical and emotional morbidity during this process.

Congenital femoral deficiency (CFD) is a comprehensive term that encompasses both the diagnosis of proximal femoral focal deficiency as well as a congenitally short femur. The incidence of CFD is approximately 1 in 50,000 to 200,000 births.¹⁷ The severity of CFD can be widely variable, ranging from a modest limb-length difference because of a short femur to a limb that has no discernible hip joint and complete absence of the femur. A constellation of limb anomalies may be associated with CFD, including acetabular dysplasia, femoral retroversion, a complex coxa vara, hypoplasia of the lateral distal femoral condyle, knee and patellar instability, as well as fibular hemimelia and its associated findings. The Paley classification of CFD is helpful in understanding the underlying pathology and dictating treatment options¹⁷ (Figure 3). A patient with less severe CFD (Paley type 1 and 2) is most likely to be a candidate for reconstruction, which consists of joint reconstruction followed by femoral and possibly tibial lengthening (Figure 4). Although tibial lengthening in patients with CFD can be associated with more complications than in patients with other etiologies, good outcomes can still be achieved.¹⁸,¹⁹ For patients with more severe CFD, other reconstruction options include rotationplasty or a Syme amputation with knee fusion.

Fibular hemimelia is the most common long bone deficiency with an incidence of 1 to 2 per 100,000 live births.²⁰,²¹ These patients present with a short limb, commonly with anteromedial tibial bowing, valgus at the knee, tarsal coalitions, a ball-and-socket ankle joint, cruciate deficiencies, femoral deficiencies, and possible absent lateral rays²⁰,²¹ (Figure 5).