Knees Bow Out, Feet Turn In, Who Cares?

Kenneth J. Noonan, MD, MHCDS

Michelle S. Caird, MD¹

¹Guru:

At some point in their career, every pediatric orthopaedist has a portion of their practice where they are asked to help parents who are concerned about their child’s limb development. Often they aren’t sure that what they are seeing is normal development or the beginning of some horrific condition that will affect their child’s life. Our jobs are to detect the few pathologic conditions and provide appropriate treatment. Just as important, in the majority of cases, we educate and assuage the fears of young parents and tell them that their child is developing normally. The young orthopaedist will stay out of trouble if they remember a few important things about the “worried well”:

Confirm with the family what they are seeing and their concerns. Empathize with their worry. Never tell a mom not to worry; unless you want to get punched.
Educate them on the range of normal development.
Explain why braces and homeopathic treatments usually can’t change what they are seeing even if they don’t like it.
Make the families feel welcome to come back to clinic if anything changes.

ORTHOPAEDICS 101: Remember to maintain a high level of vigilance as you evaluate these apparently normal children. “You may not have seen a host of rare disorders, but they may have seen you.”

Angular Deformities of the Legs

Most children seeing an orthopaedic surgeon for angular deformities of the legs are within normal limits. To stay out of trouble, the physician must be able to pick out the “abnormal” alignment by understanding normal physiologic progression of limb alignment.¹,²

Several general rules of thumb exist:

Maximum genu varum (bowlegs) occurs at birth (Fig. 27-1A)
Legs straighten at 18 months (Fig. 27-1B)
Maximum genu valgum (knock knees) occurs around age 4 years (Fig. 27-1C)
Alignment is straight to slight valgus at maturity (Fig. 27-1D)

A few important historical questions can help guide whether you should worry that a child has pathologic limb deformity and requires further consideration. Try to assess whether the child was a product of normal pregnancy and delivery. Does the child have nutritional rickets as result of being African-American and who lives in the northern climates (little sun exposure and decrease endogenous production of vitamin D) with a mom who breastfeeds him (lower calcium)? At what age did the child begin walking (Blount disease tends to occur in early walkers)? Is there a past history of infection or trauma that could lead to growth arrest or growth stimulation? Is deformity unilateral (possibly worrisome) or bilateral (less worrisome)? How is the child growing? Is he overweight, as this is a known factor leading to Blount disease in early walkers? A good screening tool is to know the child’s height on a growth curve (Fig. 27-2). A child with abnormal angulation of the legs, whose height is more than two standard deviations below normal, should be evaluated for an underlying condition such as rickets or a skeletal dysplasia. Are there any significant past history of surgical procedures (Fig. 27-3)? Is there a family history of bent or rotated bones, such as sex-linked hypophosphatemic rickets? These questions will not only demonstrate that you are concerned but will also help to discern possible pathology from the families that are convinced that Junior won’t make the Olympics unless the legs are fixed.

Figure 27-1 A: A 6-month-old with genu varum. B: An 18-month-old with straight legs. At some point in most children, usually around 18 mo of age, the legs are perfectly straight as their developmental stage passes from genu varum to genu valgum. C: A 4-year-old with genu valgum. D: An adult with nearly straight legs, erring on the side of slight valgus.

A couple of measures can be made on physical examination when trying to detect abnormal alignment and also can be used to record progression of alignment. If you are uncertain as to whether the angulation is physiologic, measure the intermalleolar distance (for knock knees) or intercondylar distance (for bowlegs). The graph in Figure 27-4 can help you decide if this is within 2 standard
deviations. This measurement can be assessed 6 months later to provide some objective evidence regarding progression or improvement. The technique of measurement can be readily taught to the family members; they will then feel that the situation is being monitored and taken seriously. In younger children, the distances may have to be measured supine, and future measurements must occur in the same position for consistency.

Figure 27-2 Any child with abnormal angulation of the legs, whose height is more than 2 standard deviations below normal, probably has an underlying condition such as rickets or a skeletal dysplasia.

Figure 27-3 A 13-year-old boy presented to clinic with concerns about how his knees look and with activity-related knee pain. He was shorter than his peers but otherwise healthy except for a remote history of “bladder surgery” at age 2. A: His alignment film demonstrated valgus with mechanical axis falling outside his knees. B, C: The careful clinician looked closely at the growth plates and noticed widening and cupping of the epiphysis (red arrows). A quick general chemistry test revealed a creatinine of 10.3. Unfortunately, he came to clinic with knee problems but left with a diagnosis of renal failure as a result of failed reconstruction for past ureter-pelvic junction obstruction. D: Nine months after renal transplantation, his knees are finally corrected with guided growth.

Figure 27-4 For each of the 12 age groups, mean values (solid circles) and 2 standard deviations (pen circles) were plotted for knee angle (A) and intercondylar or intermalleolar distance (B). Lines and shaded areas show general trends. (From Heath CH, Staheli LT. Normal limits of knee angle in white children—genu varum and genu valgum. J Pediatr Orthop. 1993;13(2):259-262.)

Figure 27-5 A: This radiograph was taken of a child with clinical unilateral genu valgum of the left leg, but the leg was externally rotated and the genu valgum is not evident. B: After the doctor drew an X on the patella and instructed the radiology technician to take the radiograph with the X pointing forward, the true genu valgum was evident radiographically.

Figure 27-6 A: Child demonstrating the apparent genu varum of tibial torsion. The chief complaint of this child’s parents was bowed legs. With the feet pointing forward the legs have the appearance of genu varum when the child is supine or walking. The apparent “bowing” is a product of the knees pointing laterally, so knee flexion gives the appearance of bowing. B: When the child’s patellas point anteriorly, it is clear that there is no significant genu varum present. This demonstration often helps alleviate parental anxiety.

Radiographs may be obtained for documentation and could be used for longitudinal comparison, provided they are of similar technique. Comparing a supine radiograph at 9 months with a weight-bearing film at 15 months is like comparing apples to oranges. The weight-bearing status of the radiographs has to be the same, or differences in deformity may be falsely attributed to progression or improvement. While taking radiographs, it is important that the patellas (not feet) are pointing forward (Fig. 27-5). In the case of a child with tibial torsion, if the feet point forward, the patellas point laterally and may give a false impression of genu varum radiographically and clinically (Fig. 27-6A). Clinically, the parents (and even clinician) may mistakenly think a child with tibial torsion is bowlegged. As Figure 27-6B demonstrates, turning the legs inward so the patella points straight anterior allows assessment and demonstration of varus/valgus alignment.

GENU VARUM

Here is the classic scenario: 18-month-old boy named Babe Ruth with bilateral bowlegs is accompanied to clinic with mom, dad (wearing his tattered Major League baseball jersey), and both grandmothers who have menacing looks for the “young-looking” doctor. The first step is to determine whether Babe is growing well; if he is of normal stature and height, you can rule out skeletal dysplasia and metabolic bone disease. Now you have to differentiate between physiologic
genu varum (>95% likely) and Blount disease, which at this age is often quite difficult. On physical examination, you cover up the foot and rotate the knee until the patella is pointing to the ceiling. If he has valgus knees, he has internal tibial torsion that looks like varus when he walks and not Blount disease. If the knee “might be” in a bit of varus, the child could still have either diagnosis. Radiographs are unlikely to show “definitive” signs of Blount disease (metaphyseal beaking and epiphyseal fragmentation) until after 2 years of age. This may be problematic with respect to confirming the diagnosis and selecting the optimal timing and method of treatment (Fig. 27-7). Radiographs at 18 months of age may be “predictive” for developing Blount disease. A metaphyseal-diaphyseal angle greater than 16° increases the likelihood of a diagnosis of Blount disease but is by no means definitive. Stay out of trouble by not relying too heavily on a radiographic diagnosis of Blount disease in children less than 2 years of age. Radiographs do still have value at this time point; a standing alignment film could be taken as the child leaves clinic and could be compared to future films should Babe fail to straighten out. NEWSFLASH! Today’s smartphones are a useful tool for parents to follow their children. Have them take a frontal picture of the child standing in a diaper and set the alarm for 6 months. When the alarm goes off, they can pull up the picture and compare to the child. If the kid is worse, they should come back for comparative X-rays.

Genu Varum: Suspect Blount Disease When…

Child is older than 2 years
There is lateral thrust (as weight is placed on a leg during the stance phase of gait, the knee abruptly translates laterally) (Fig. 27-8A)
Focal angulation on examination and radiograph at proximal tibia is observed (Fig. 27-8B)
There is medial beaking and downward slope of the proximal tibial metaphysis on radiographs. These radiographic changes cannot be detected before 2 years of age (Fig. 27-8C)
Parents report it is not improving

These Associations Raise Level of Suspicion

Obesity
African-American ethnicity
Early walker
Unilateral occurrence

TREATMENT OF INFANTILE BLOUNT DISEASE

The use of orthotics to unload medial compressive forces may, according to some investigators, alter the natural history of infantile Blount disease. Others recognize that these straight leg braces (no knee joint) are very challenging for parents and children as they are hard to fit on obese children and that have to be worn during the day. While many aspects of orthotic treatment are controversial, bracing proponents feel that this should be started before the age of 3 years.³

Two surgical options exist for the child older than 3 years with progressive varus and radiographic changes consistent with infantile Blount disease—growth
plate modulation and osteotomy. The choice requires shared decision-making with the family. Guided growth with temporary hemiepiphysiodesis of the lateral (Fig. 27-9) may correct the deformity.

Figure 27-7 A: A 3-year-old with bowed legs next to his older brother. The mother reported the older brother had bowed legs just as bad as his younger brother but grew out of it without any treatment. B: Radiograph of the 3-year-old shows generalized bowing of the femurs and tibia. There is not a focal deformity of the proximal tibia that would be expected with Blount disease, and the physes appear normal. Given the child’s severity of bowing and age, treatment would generally be indicated for genu varum. In the context of the family history and radiographs suggestive of physiologic bowing, however, the child was followed up with close observation only. C: Radiograph of the same child at age 5 y demonstrates resolution of the genu varum without treatment. (Courtesy of John T. Killian, MD.)

To stay out of trouble, the patient should be less than 4 years of age, and no bony bar should be present in the medial physis. Modular screw and side plate constructs are preferred as standard Blount staples don’t get as good as purchase in the immature tibia and its preponderance of unossified cartilage (Fig. 27-10).
The child with infantile proximal tibia vara and excessive internal tibial torsion may not be a good candidate for guided growth as it is debated that guided growth actually changes rotation.

Figure 27-8 Signs of Blount disease. A: During weight bearing, a lateral thrust of the knee is suggestive. B: Focal angulation at the proximal tibia and medial beaking of the tibia are suggestive. C: Medial tibial beaking and downward sloping of the metaphysis are characteristic.

Figure 27-9 A, B: A 3½-year-old boy with bilateral infantile Blount disease. C: He underwent guided growth after MRI demonstrated no bony bar, even though the right growth plate (yellow arrow) looks more affected than the left growth plate (red arrow). Modular plate and screw implants were placed. D, E: Follow-up at 22 and 31 months reveals asymmetric improvement. To stay out of trouble, the surgeon must continue to follow the patient until full correction and consider implant removal versus complete epiphysiodesis to avoid the high chance of recurrence, especially on the right.

When contemplating osteotomy, there are some common areas of potential trouble that the surgeon should be aware of. The best outcomes from osteotomy are found in children who are younger than 4 years to minimize the risk of recurrence of deformity.⁴,⁵ To stay out of trouble in children who are older than 4 years; obtain an MRI to rule out a bony bar (Fig. 27-11). A child with deformity and a bony bar could be treated with bar excision in addition to osteotomy. Proximal tibia and fibula osteotomies have significant risk of compartment syndrome. The anterior tibial artery passes through the interosseous membrane near the level of the osteotomy. Acute correction through the osteotomy site is believed to cause occlusion of the artery and lead to compartment syndrome at times. Acutely lessening the degree of correction has relieved signs of ischemia in some cases.⁶ Anterior compartment release at time of correction should be performed, and careful postoperative monitoring is essential. It may be wise to avoid an epidural catheter because it might mask symptoms of compartment syndrome.

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