Pediatric Lower Limb Deformity
Pediatric lower limb deformity is a broad category of conditions that may be idiopathic or associated with an underlying congenital disorder. Clubfoot and other deformities of the feet are among the most common lower limb deformities and are further elaborated in separate chapters. Here, leg length discrepancy, in-toeing, and bowed legs will be reviewed as examples of longitudinal, rotational, or angular limb deformities.
Structure and Function
To identify abnormal, one first needs to identify normal. Although it might be reasonably expected that a person’s legs should be straight and of the same length, a small leg length discrepancy or angulation can be seen in more than half of the US population.
Normal limb alignment is dependent on age. Alignment deformities can either be angular or rotational. Prior to age 2 children, have a relatively varus (bow leg) alignment in the frontal plane and this gradually becomes valgus (knock knee) as they grow. Typically, by age 7, children have a final femoral-tibial alignment of 5-6 degrees of valgus. Most rotational deformities are symmetric and considered variations of normal that typically improve with age.
Femoral rotation is defined as the angle of the femoral neck in the axial plane relative to the femoral shaft. The best way to think about femoral rotation is to consider a denuded femur resting on a flat surface. If the posterior femoral condyles are lying flat, the femoral neck will form an angle with the surface, with the head rising off the surface (Figure 1).
The femur can be either anteverted (Figure 2) or retroverted.
Femoral anteversion is more common in females, greatest in infancy with an average of 40°, and gradually decreases with age to an average of 16° at maturity. When the femur is anteverted, internal rotation of the lower extremity will tend to orient the femoral head to the center of the acetabulum (Figure 3).
Tibial rotation is defined as the inward or outward rotation of the foot as it relates to the knee. Normal intrauterine packing typically leads to internal tibial torsion that steadily progresses to slight external tibial torsion at maturity.
Although bowing at the knees is considered normal up until age 2, the angulation of the leg may be due to a deformity of the tibia itself, a condition known as “infantile tibia vara” or Blount’s disease. (The term “varus” comes from a Latin word meaning “bent” but refers specifically to a bend or angulation of a bone or joint in which the distal part is more medial than it should be. In tibia vara, the foot is more medial than it would be had the tibia been straight. [When the distal part is more lateral, the deformity is denoted “valgus”.]) Blount’s disease can more readily be identified between the ages of 2-5 years old both clinically and radiographically. It is commonly seen in obese children, early walkers, as well as Hispanics and African Americans. Frequently it can be associated with in-toeing as well. Although much less common, children can present older than 10 years of age. These cases are denoted as adolescent Blount’s disease. Adolescent Blount’s disease is typically a less severe form. In addition, it is frequently associated with femoral deformity as well, and is more likely to be unilateral.
All patient’s presenting with a concern of a lower limb deformity warrant a thorough history and physical that at minimum must include a birth history, family history, developmental milestones, gait analysis, neurological exam, limb measurement, and rotational profile.
Leg Length Discrepancy
While the effects of leg length discrepancy can vary, most patients are asymptomatic. Parents are usually the first to report a discrepancy when they relay concerns about the way their child walks.
Children may present with a limp. Some report tiring easily with ambulation due to increased exertion required because of the discrepancy, and some complain of lower back pain.
A thorough gait analysis should be performed on every patient with suspected leg length discrepancy as well as clinical measurement of each limb.
Measurement can be performed using a tape measure from the anterior superior iliac spine to the medial malleolus in either supine or standing position or with block testing.
Block testing is performed with the patient standing using a series of blocks under the short leg until the iliac crests are level and then measuring the size of the block to determine the discrepancy.
In children who present with a leg length discrepancy at a very young age and are too young to ambulate, the physician must evaluate for a potential hip dislocation as the cause of the leg length discrepancy.
Parents complaining of their child walking or running with in-toeing (more commonly referred to as being “pigeon-toed”) is an extremely common presentation in both the primary care and orthopedic setting. Most children initially present shortly after they begin walking. While most children are asymptomatic, parents often report that their child falls or trips frequently.
Because of the possibility of Blount’s disease causing the angular deformity, any toddler with bowed legs should be followed closely with serial examination. However, genu varum is not likely to suggest Blount’s disease in children under the age of 18 months, unless the overall deformity is severe or there is a sharp angulation of the proximal tibia.
Leg Length Discrepancy
The most accurate method of assessing leg length discrepancy is full length (hip to ankle) radiographs, radiographic scanography or computerized tomography (CT).
Radiographic scanography (Figure 4) is a series of images of both legs with a ruler that are stitched together to allow measurement of the limb. CT scanography can be used similarly but additionally can assess for limb alignment and rotation. Newer imaging technologies also exist which utilize a low dose biplanar radiograph which can give accurate limb length measurements with less radiation than conventional XR (EOS Imaging). Bone age should additionally be assessed to determine the estimation of progression.
When evaluating patients with in-toeing, radiographic evaluation is not usually required.
The exam should begin with a gait analysis. The “foot progression angle” (FPA) should be observed: this is the angle made by the long axis of the foot and the line of progression of gait (“straight ahead” as the patient walks). A negative FPA indicates in-toeing and a positive FPA out-toeing. A normal range is typically -5 degrees to +20 degrees, but can be variable with age. Once the FPA is determined to be abnormal, the next step is to localize the source of the deformity, i.e. hip, tibia, or foot.
Assessment of femoral rotation, or hip version, is performed with the patient prone on the exam table, knees bent to 90 degrees, and the legs maximally internally and externally rotated (Figure 5 Left and Center). Significantly greater internal rotation (typically greater than 70 degrees) with a decreased amount of external rotation (typically less than 20 degrees) is often indicative of increased femoral anteversion or internal rotation of the femur.
From the prone position, the thigh-foot angle (Figure 5, right) and transmalleolar axis can be examined to assess for tibial torsion. The thigh-foot angle is the angle formed by the axis bisecting the foot and the axis bisecting the thigh. The transmalleolar axis is the angle formed by axis of the malleoli of the ankle with the coronal plane of the tibia. Similar to FPA, inward rotation is designated a negative value and external rotation a positive value. Infants typically present with a negative thigh-foot angle and transmalleolar axis and progress to a more neutral or positive angle as they get older.
Lastly, a thorough foot exam should be performed. Patients who in-toe may have an apex or curve to their lateral foot rather than a straight lateral border, a sign indicative of possible metatarsus adductus. Additionally, this will often present with a medial plantar crease. The heel bisector line can be examined, which is the axis of the heel exiting at the level of the toes. If the line exits through the 2nd and 3rd toe, this is considered normal, as the line exits more laterally from the toes this is a demonstration of forefoot adductus. Examiners should determine if such a deformity is rigid or flexible (passively correctable to neutral or beyond).
True infantile and adolescent Blount’s disease bowing will generally be grossly evident on exam or with ambulation.
For patients over the age of 18 months, varus alignment of the tibia on exam should prompt an x-ray. (It is generally not recommended to perform radiographs prior to this age regardless of the exam.)
The metaphyseal-diaphyseal angle of the tibia should be measured on all radiographs ordered to rule out tibia vara (Figure 6). An angle less than 10 degrees is considered normal and likely to resolve with time. Any angle greater than 10 degrees is considered abnormal and should be followed closely with serial exams and radiographs.
In more severe cases, metaphyseal beaking of the tibia as well as inferior and posterior sloping of the proximal epiphysis can be seen (Figure 7). Additionally, radiographic standing alignment films can be used to assess for angular deformity and determine the mechanical axis of the lower extremity.
Leg Length Discrepancy
Leg length discrepancy can present as a result or combination of the following:
- Trauma: Long bone fractures are one of the most common causes of leg length discrepancy. A shaft fracture in a growing child can often times lead to accelerated growth in that extremity causing it to become longer than the contralateral leg. Alternatively, a fracture that heals in a shortened position or a fracture through the growth plate of a long bone can lead to a shortened extremity.
- Infection: Bone infections in pediatric patients, especially when involving the growth plate.
- Congenital disorders or dysplasias:Includes hemihypertrophy, proximal femoral focal deficiency, developmental dysplasia of the hip, fibular and tibial hemimelia, unilateral clubfoot, neurofibromatosis, multiple hereditary exostoses, idiopathic or neuromuscular scoliosis.
- Paralytic disorders: Includes cerebral palsy (due to spasticity and contractures) and polio.
In-toeing conditions are considered packing disorders caused by intrauterine positioning but may carry some hereditary component as they frequently run in families. They can present as a result or combination of the following:
- Metatarsus adductus: Most commonly presents in infants. Must additionally rule out skewfoot, congenital hallux varus, and clubfoot.
- Internal tibial torsion: Most commonly presents from 1-3 years of age.
- Femoral anteversion: Most commonly presents in children greater than 2 years of age.
Bowed legs most commonly present as physiologic tibia vara that resolves by 2 years of age. Persistent bowed legs beyond the age of 18 months are considered pathologic and can be a result of or associated with any of the following:
- Infantile tibia vara (Blount’s): pathologic genu varum in children 2-5 years old
- Adolescent tibia vara (Blount’s): pathologic genu varum in children greater than 10 years old. More often unilateral than infantile tibia varum which is most commonly bilateral (Figure 8).
- Congenital disorders or dysplasias: Multiple epiphyseal dysplasia, spinal epiphyseal dysplasia, focal fibrocartilaginous dysplasia, osteogenesis imperfecta, multiple hereditary exostosis, Maffucci syndrome, Ollier disease, congenital pseudarthrosis of the tibia (anterolateral bowing).
- Metabolic bone disease: Rickets (Figure 9), renal osteodystrophy.
- Acquired: Trauma, radiation, infection.
Treatment Options and Outcomes
If a congenital disorder/dysplasia or metabolic bone disease is suspected, a referral to a geneticist for formal testing might be helpful (though for some condition congenital disorders, e.g. fibula hemimelia, a genetics workup is fairly uncommon).
Leg Length Discrepancy
Treatment of leg length discrepancy in the pediatric patient is dependent on the cause and the projected discrepancy at skeletal maturity. If an underlying condition such as scoliosis, infection, or hip dysplasia is the cause of the leg length discrepancy, the condition should be addressed first and then the leg length discrepancy if still present.
In general, if the projected leg length discrepancy (based on future growth) is 2 cm or less, the best treatment approach is observation with shoe lifts if needed.
A projected leg length discrepancy of 2 to 5 cm has usually been treated with shortening procedures of the longer limb, such as an epiphysiodesis (i.e., surgical ablation of a physis to arrest growth).
A leg length discrepancy expected to be 5 cm to 20 cm is treated with lengthening procedures such as distraction osteogenesis. A lengthening procedure can sometimes be combined with a shortening procedure on the contralateral “long” leg.
Note that the precise cutoff at which a lengthening procedure should be used is evolving, as surgical techniques have improved. After a shared decision making process in which the family considers the risks and benefits, it may be reasonable to employ a lengthening procedure for a discrepancy of 4 cm or less.
If the projected leg length discrepancy is 20 cm or more, amputation is highly recommended.
A majority of children with bowed legs can be treated with observation alone with spontaneous resolution expected between the ages of 2-3 years old. Mild bowing that persists beyond this age can be treated with a Knee-Ankle-Foot-Orthosis (KAFO), though this has had mixed results. More severe bowing or persistent bowing beyond the age of 4 should warrant a consideration of surgery. Surgical options include proximal tibia-fibula osteotomies, guided growth with lateral hemiepiphysiodesis, or medial epiphysiolysis (bar resection). Oftentimes these surgeries are performed in combination.
(Additional information about this rare condition is provided in this excellent review: Congenital Pseudarthrosis of the Tibia, Journal of the American Academy of Orthopaedic Surgeons: April 2008 - Volume 16 - Issue 4 - p 228-236)
In the vast majority of cases, in-toeing is treated non-operatively, coupled with parental reassurance and education. Most children will grow out of in-toeing as they age. These children should not have restrictions and should participate in activities similar to their peers.
In cases of rigid metatarsus adductus (that is, if the foot does not passively correct to neutral) serial casting can be performed. In even rarer cases of severe femoral anteversion or internal tibial torsion that do not improve by the age of 8 years old leading to significant cosmetic and functional disability, correctional osteotomy can be considered.
Create a differential diagnosis for in-toeing. Understand clinical test to assess rotational profile of lower extremities. Know how to image for a leg length assessment. Understand the natural history of lower extremity alignment with age.
anteversion, in-toeing, valgus, varus, retroversion