ANGULAR DEFORMITIES OF THE LOWER LIMBS IN CHILDREN Robert N. Hensinger, M.D. Section of Orthopaedic Surgery University of Michigan Hospital TC 2914/0328 Ann Arbor, MI 48109 INTRODUCTION thrust (genu varum) or medial thrust (genu valgum) occurs Angular malalignments, bow legs and knock knees, are (Fig. 1). Children with physiologic varus or valgus angu- a common concern in the early years of life. For the lation at the knees typically do not exhibit a thrust. How- majority of children, the problem represents a normal ever, in pathologic conditions a thrust is often present physiologic variation, and spontaneously corrects12'27'32. suggesting incompetence of the knee ligaments. Ligament A few will have pathologic malalignment leading to cos- incompetence increases the potential for continued pro- metic or functional problems requiring bracing or surgery. gression of the deformity37. Familiarity with the natural history of angular deformities The natural history of physiologic genu varum and genu and familiarity with normal growth patterns are necessary valgum has been defined by Salenius and Vankka32. They to evaluate malalignment. studied the development of the tibiofemoral angle in 1480 normal children (Fig. 2). The tibiofemoral angle within the PHYSIOLOGIC BOW LEGS AND KNOCK KNEES first year is 150 of varus. As the child approaches 18 months, the angle gradually increases to neutral, and the Clinical evaluation of angular deformities should include lower extremities appear straight. During the second and family history, any description of onset and information third years, the tibiofemoral angle increases to an average about progression of the deformity. A child who has of 12° of valgus. During the following years, the valgus assymptomatic findings or a brief history of rapid progres- alignment slowly decreases to that of the adult, 70 in male sion is particularly suspect because these suggest a seri- and 80 in females. When obtaining an AP roentgenogram ous condition such as a neurologic disorder, congenital of the knees to measure the tibiofemoral angle, the legs anomaly, tumor or infection. must be positioned in neutral rotation; external rotation The normal infant usually stands with the legs apart, will decrease valgus deformity and internal rotation will and the subcutaneous fat may mask early physiologic varus increase valgus angulation18. angulation. Internal tibial torsion often accompanies phys- iologic genu varum, and accentuates the bow-leg appear- +.15 ance while standing or walking. Pes planus and external tibial torsion may accompany genu valgum and similarly VARUS +10°F accentuate the appearance of knock knees. The child should be observed walking, with attention to + 5o the knees the stance phase to determine if lateral during 2 3 4 6 7-13 AA (YFRq-- L I * MM t T LSU% )r I1 - 50 VALGUS -101- Figure 1 Child with unilateral bow leg, dem- - 151_ onstrates the lateral thrust at stance phase. The weightbearing Figure 2 force is transmitted through the Development of the tibiofemoral angle during growth. Repro- medial tibiofemoral compartment, duced with permission from J. Bone and Joint Surg., 75A:259- slowing the growth of the medial 261, 1975. tibial physis. In the past, authors have recommended using the dis- tance between the femoral condyles to measure genu varum and the distance between the malleoli of the ankles to measure genu valgum27,30. These measurements have never been shown as accurate or reproducible and do not allow for the normal variation in leg length. 16 The Iowa Orthopaedic Journal Angular Deformities of the Lower Limbs in Children DIFFERENTIAL DIAGNOSIS OF GENU VARUM BLOUNT'S DISEASE In the young child, Blount's disease is the most common Blount's disease, osteochondrosis deformans tibia, was cause of pathologic genu varum. However, the child should initially described by Erlacher in 1922 and the first large be evaluated to exclude other causes such as metaphyseal series was reported by Blount in 19375,13. Blount described dysplasia (Fig. 3), osteochondromatosis, hemihypertro- both an infantile and an adolescent form. The infantile form phy, fibular or tibial hemimelia, multiple epiphyseal dyspla- is usually bilateral, progressive, associated with internal sia, osteochondrodystrophy, achondroplasia and fibrous tibial torsion, and appears as a pathologic continuation of dysplasia16. Trauma or infection involving the physis or physiologic genu varum. The adolescent form is less com- epiphysis and fracture of the adjacent metaphysis can also mon, occurring in older children (9-14 years of age), typ- result in varus deformity. Bone softening conditions such ically unilateral and less often associated with internal tibial as rickets can cause varus or valgus knee deformities. torsion. Both forms are more common in blacks2'3"10'15. Usually the direction of the deformity is dependent on the Infantile tibia vara is a developmental problem charac- child's alignment at the onset of the condition. Thus, the terized as an abrupt angulation of the medial tibia, due to various forms of rickets can be associated with either genu a disturbance in growth of the posterior medial portion of varum or genu valgum. Onset of vitamin D deficiency or the proximal tibial epiphysis. In the advanced stages of vitamin D resistant rickets during the "bow-leg phase" will this condition there is an associated depression in the lead to more pathologic bowing. Genu valgum is typically posterior medial portion of the proximal tibia36. Pathologic associated with renal osteodystrophy because the onset reports are sparse but demonstrate irregular cartilage of chronic renal disease generally occurs while children are columns, scattered areas of hypertrophic chondrocytes, in the valgus phase. Metabolic conditions such as rickets hypocellular fibrocartilage and delayed irregular ossification. affect the entire epiphyseal plate, while Blount's disease There is disagreement as to the etiology of the condi- involves only the medial aspect of the proximal tibia. tion. Langenskiold and Riska, and Blount all believed that it is caused by disturbance in growth and ossification of the medial part of the proximal tibial epiphysis and metaphysis5'6'24. However, it is not due to avascular necro- sis, infection or nutritional factors6"14'21'24. There are only scattered reports of familial bowing33'34'41. Others suggest that the problem develops as a result of early walking Three year old with meta- when physiologic genu varum is maximal. The weight physeal dysplasia. Findings bearing force is then transmitted across the medial tibiofe- inthe proximal tibia are sim- ilar to Blount's disease, moral compartment slowing the growth of the medial tibial however, similar changes are physis1 2'3'4'9"6' 19 If a lateral thrust has developed with found in the other meta- weight bearing (Fig. 1) in a child with genu varum, the physes of the lower extrem- ity, suggesting a generalized prognosis for improvement is poor37. Burke developed a condition. biomechanical model that demonstrates that in the 2 year old, 20 degrees of varus results in sufficient force to retard epiphyseal growth. In the 5 year old, only 10 degrees is needed to retard epiphyseal growth7. Langenskiold and Riska described six stages of roent- genographically visible progression based on epiphyseal Hypophosphatasia is an inborn error of metabolism depression and metaphyseal fragmentation of the proximal characterized by low alkaline phosphatase activity. There medial tibia24. The children were grouped by radiographic are many forms of this condition, and the severely involved appearance (stage I through VI), depending on the degree child is not likely to survive infancy. Less severely involved of epiphyseal depression and metaphyseal fragmentation chdren have radiographic findings siinlar to vitamin D (Fig. 4). Medial fragmentation of the proximal tibial meta- resistant rickets. Children with hypophosphatasia, renal physis is the minimal finding for stage I (Fig. 5A). Isolated rickets and nutritional rickets have osteopenic bone while tibial bowing or beaking of the metaphysis is not consid- patients with vitamin D resistant rickets are likely to have ered diagnostic3 9. As the condition progresses, an increased normal bone density. varus angulation is noted just distal to the proximal tibial The radiographic appearance of the epiphyseal plate in epiphyseal plate (Fig. 5B). The epiphyseal line medially metaphyseal dysplasia is similar to rickets (Fig. 3). These becomes irregular and the epiphysis slopes medially (Figs. children have varying degrees of involvement from mark- 6A-B, 7A-B). As tensile forces increase laterally, there is edly disturbed metaphyses, to mild involvement of the often an accompanying widening of the epiphyseal plate distal femur or proximal tibia. and tilting of the epiphysis7. Volume 9 17 R. N. Hensinger IV Ii III I v v Figure 4 Schematic drawing of the Langenskiold classification, depicting the six stages of progressive radiologic change of tibia vara from mild to severe. The higher stages have more medial deformity and fragmentation. age II Figure 6A-B (A) Langenskiold stage III. Note the sloping of the medial epi- physis. The metaphysis demonstrates further dissolution, frag- mentation and collapse. (B) Langenskiold stage IV. Sloping and further fragmentation of the proximal tibial metaphysis. Note the disappearance of the medial portion of the tibial epiphysis. Figure 5A-B (A) Radiograph of Langenskiold stage I demonstrating mild blunting of the medial