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Approach to the child with knock-knees

Approach to the child with knock-knees
Literature review current through: Jan 2024.
This topic last updated: Feb 14, 2023.

INTRODUCTION — Knock-knees (genu valgum) is an angular deformity at the knee where the apex of the deformity points toward the midline (figure 1). Bow-legs (genu varum) is an angular deformity at the knee where the apex of the deformity points away from the midline.

Bow-legs and knock-knees are among the most common musculoskeletal anatomic variations encountered by pediatric primary care providers and a common reason for referral to a pediatric orthopedic surgeon. However, most children with knock-knees or bow-legs have variations of normal lower-extremity development and can be monitored by the primary care provider.

An understanding of the normal physiologic development of the lower extremity is essential in differentiating physiologic from pathologic alignment. Pathologic causes of knock-knees include posttraumatic (eg, Cozen fracture), rickets (eg, renal osteodystrophy), skeletal dysplasias, mucopolysaccharidosis, and neoplasms. Unlike physiologic knock-knees, these conditions generally do not improve over time and may require treatment with bracing or surgery.

This topic will provide an overview of normal physiologic alignment of the lower extremity, physiologic and pathologic causes of knock-knees, and an approach to the child with knock-knees. Bow-legs are discussed separately. (See "Approach to the child with bow-legs".)

NORMAL PHYSIOLOGIC ALIGNMENT — An understanding of normal physiologic development of the lower extremity is essential to differentiation of physiologic from pathologic deformities. Lower-extremity alignment goes through a predictable progression from varus (bow-legs), to neutral, to valgus (knock-knees), and back towards neutral over the first seven years of life (figure 2 and figure 3) [1]. Final adult lower-extremity alignment is slightly valgus. There is a wide range of normal values [1,2].

At birth, normal alignment is varus.

As the child begins to stand and walk, the amount of varus often increases. Children who walk at an early age may have greater varus alignment [3].

Around 18 to 24 months of age, alignment should be neutral.

After 24 months, alignment should progress to valgus until it reaches a maximum at four years.

After age four years, valgus alignment should decrease toward physiologic adult alignment of slight valgus to neutral.

By age seven years, a child usually has reached their adult lower-extremity alignment of slight valgus.

CAUSES OF KNOCK-KNEES — Causes of genu valgum include physiologic valgus (most common), posttraumatic (eg, Cozen fracture, distal femoral physeal fracture, proximal tibial physeal fracture), systemic/metabolic conditions (eg, rickets, mucopolysaccharidosis type IV), skeletal dysplasias (eg, chondroectodermal dysplasia) and neoplasms (eg, multiple hereditary exostoses) (table 1) [2,4-6]. (See "Skeletal dysplasias: Specific disorders" and "Skeletal dysplasias: Approach to evaluation" and "Nonmalignant bone lesions in children and adolescents", section on 'Osteochondroma and hereditary multiple osteochondromas'.)

Physiologic valgus — Genu valgum is part of normal development between two and five years (figure 2). In physiologic valgus, the tibiofemoral angle is within two standard deviations of the mean for age (figure 3). Maximal physiologic valgus is usually reached by age four or five years. Spontaneous correction occurs during the next few years until the child reaches the adult alignment of slight valgus to neutral.

Characteristic features of physiologic valgus include:

Age between two and five years

Symmetric valgus deformities

Normal stature

Lack of symptoms, although in severe cases the child may have difficulty running or complain of anterior knee pain

Flat feet and external tibial torsion may accompany physiologic valgus and can accentuate its appearance [5]. (See "Forefoot and midfoot pain in the active child or skeletally immature adolescent: Overview of causes", section on 'Arch abnormalities' and "Approach to the child with out-toeing", section on 'External tibial torsion'.)

Pathologic valgus — Pathologic valgus may occur after trauma, in association with a number of systemic/metabolic conditions, skeletal dysplasia, or neoplasms (table 1).

Clinical and radiographic features help to distinguish physiologic from pathologic valgus. Clues to pathologic valgus include age <2 years or >7 years, unilateral valgus, short stature, medial thrust (brief medial knee-joint protrusion during the stance phase of gait that suggests incompetence of the knee ligaments), asymmetry, and progression rather than improvement after four to five years of age (table 2) [2,5-10].

Posttraumatic — Patients with open growth plates may be at risk for developing valgus deformity following fractures. Deformities related to trauma are unilateral and alignment is asymmetric.

Cozen fractures – Children younger than 10 years of age who sustain a fracture of the proximal tibial metaphysis are at risk for developing valgus deformity secondary to selective medial physeal overgrowth in response to the fracture or the healing response [2,11,12].

This posttraumatic valgus deformity may occur even in minimally displaced fractures that maintain good alignment and heal successfully (image 1). Thus, all proximal tibial fractures in children younger than 10 years should be followed over time to ensure maintenance of alignment. Deformity usually develops within one year of injury [13]. (See "Proximal tibial fractures in children".)

Growth arrest from physeal fractures – Fractures involving the distal femoral or proximal tibial physis may result in growth arrest. If the lateral aspect of the physis is damaged, a valgus deformity may develop (image 2). (See "Distal femoral fractures in children".)

Other causes — Knock-knees also may be caused by [5,14,15]:

Rickets and other systemic/metabolic medical problems (eg, mucopolysaccharidosis) (see "Overview of rickets in children" and "Mucopolysaccharidoses: Complications", section on 'Genu valgum' and "Pediatric chronic kidney disease-mineral and bone disorder (CKD-MBD)")

Skeletal dysplasia (eg, multiple epiphyseal dysplasia, pseudoachondroplasia) (see "Skeletal dysplasias: Specific disorders")

Neoplasms (eg, multiple hereditary exostoses) (see "Nonmalignant bone lesions in children and adolescents", section on 'Osteochondroma and hereditary multiple osteochondromas')

Significant valgus deformity (ie, intermalleolar distance >8 cm [approximately 3 inches] with patellas facing straight ahead and the femoral condyles touching (figure 4)) and short stature are clues to these pathologic causes of knock-knees. (See 'Evaluation' below.)

CLINICAL PRESENTATION — Presenting complaints for children with knock-knees may include concerns about the appearance of the legs, clumsiness, falling, flat feet, and medial foot or knee pain.

EVALUATION — The physical examination is the most important component of the evaluation of the child with knock-knees. Radiographs are necessary in a minority of cases. (See 'Radiographs' below.)

History — Important aspects of the history in a child with knock-knees include [5-8,10]:

Growth and development

Onset (ie, before or after birth? Before or after walking?)

Progression (physiologic valgus typically progresses between ages two and four years and improves between age four and seven years; pathologic valgus worsens after age four years)

Associated complaints (pain, limp, tripping, falling)

Previous treatment (if any) and treatment response

History of lower-extremity infection, trauma, or fracture (that may have caused asymmetric growth retardation or stimulation)

History of joint swelling/warmth (suggestive of infectious or inflammatory arthritis)

Family history (short stature, skeletal dysplasia)

It is also important to ascertain the caregivers' perceptions of the deformity and concerns regarding gait, appearance, and function.

Physical examination — Important aspects of the physical examination of the child with knock-knees include [5-7,10]:

Length/height – The child's length or height should be plotted on the standardized growth curve ( (figure 5A-B) [for males] and (figure 6A-B) [for females]). Length/height less than the 3rd percentile in a child with knock-knees is a potential clue to a pathologic condition (eg, renal osteodystrophy, skeletal dysplasia) [16]. Less severe short stature (eg, 10th or 25th percentile) may be cause for concern if the child has other manifestations of a pathologic condition associated with knock-knees (table 1). (See 'Other causes' above.)

Weight – The child's weight should be measured and body mass index calculated ((calculator 1) [for males] and (calculator 2) [for females]). Obese children may develop idiopathic genu valgum [2,5]. (See "Clinical evaluation of the child or adolescent with obesity".)

Focused examination of the lower extremities – Focused examination of the lower extremities in young children may be easier if performed with the child sitting on the caregiver's lap. With the child in the seated position, the knees should be extended and the legs rotated so that the patellas are pointed straight ahead. This maneuver is necessary to accurately estimate lower-extremity angular alignment because it removes any apparent varus or valgus that may be caused by tibial torsion or femoral anteversion. Flat feet and external tibial torsion may accompany knock-knees and accentuate its appearance [5].

With the knees extended, the patellas pointed straight ahead, and the femoral condyles touching, a gross estimate of the amount of valgus can be measured (figure 4). Greater than 8 cm (approximately 3 inches) between the medial malleoli is considered abnormal at any age [17]. This measurement provides a reproducible, objective, nonradiographic method of monitoring progression or improvement of the deformity over multiple clinic visits.

Additional components of the lower-extremity examination include [5,7]:

Assessment of symmetry, including leg-length discrepancy (asymmetry or unilateral involvement is suggestive of pathologic genu valgum)

Assessment of leg length (shortening of the legs may suggest skeletal dysplasia) (table 1) (see "Skeletal dysplasias: Approach to evaluation", section on 'Physical examination')

Determination of the site of angulation:

-Proximal tibia – Cozen fracture

-Knee – Ligamentous hyperlaxity, arthritis

-Distal femur or distal femur and distal tibia – Metabolic bone disease, skeletal dysplasia

Assessment of the iliotibial band for tightness with the Ober test (picture 1)

Palpation of the epiphysis and metaphysis for exostoses (a clue to hereditary multiple osteochondromas) [18]. (See "Nonmalignant bone lesions in children and adolescents", section on 'Osteochondroma and hereditary multiple osteochondromas'.)

Observation of gait – If the child is ambulatory, the child's gait should be observed as the child walks toward and away from the examiner [2]. The foot progression and patellar progression angles should be noted. These angles describe the alignment of the foot and patella, respectively, as they relate to the direction that the patient is moving. For example, an internal foot progression angle describes a foot that points toward the midline as the patient walks forward. An external patellar progression angle describes a patella that points laterally as the patient walks forward.

The presence or absence of a medial thrust during ambulation also should be noted [5]. A medial thrust is a brief medial knee-joint protrusion during the stance phase of gait that suggests incompetence of the knee ligaments. A medial thrust may be characteristic of pathologic genu valgum.

Radiographs — Patients who fit within the age-appropriate progression of valgus rarely need radiographs (figure 2 and figure 3). (See 'Normal physiologic alignment' above.)

Indications – We suggest that radiographs be obtained in children with clinical features suggestive of pathologic valgus (table 2) [5-10].

Technique – Proper radiographic technique is essential to obtaining useful images. If possible, teleograms (the entire lower extremity from the hips to the feet of both lower extremities) should be obtained with the patient standing (image 3). Whether the child is standing, it is paramount that the patellas (not the feet) are pointing straight ahead. Otherwise, the amount of valgus cannot be accurately assessed. Proper positioning permits serial comparison if necessary [2].

Findings – The radiographs are reviewed to [6,7,10]:

Determine which bones are affected (eg, femur, tibia, or both)

Determine which aspects of the bone are involved: bony diaphysis (trauma), metaphysis (skeletal dysplasia, Cozen fracture), physis (rickets, skeletal dysplasia, growth arrest from physeal fracture), epiphysis (skeletal dysplasia)

Measure the tibiofemoral angle (the angle between the long axis of the tibia and the long axis of the femur)

Assess the width of the physis (growth plate) and height of the epiphysis

Look for characteristic features of skeletal dysplasias (eg, flattening of the distal and proximal femoral epiphyses in multiple epiphyseal dysplasia) (see "Skeletal dysplasias: Specific disorders")

Additional evaluation — Additional evaluation may be necessary if radiographs are suggestive of metabolic bone disease or skeletal dysplasia (table 1). The evaluation varies depending upon the suspected condition. (See "Pediatric chronic kidney disease-mineral and bone disorder (CKD-MBD)" and "Overview of rickets in children" and "Mucopolysaccharidoses: Clinical features and diagnosis" and "Skeletal dysplasias: Approach to evaluation".)

INDICATIONS FOR REFERRAL — We suggest that children with clinical features suggestive of pathologic valgus (table 2) be referred to an orthopedic surgeon and/or other specialist as indicated by the suspected underlying condition (eg, nephrologist, endocrinologist, geneticist, rheumatologist) [8,10].

MANAGEMENT

Physiologic knock-knees — The natural history of physiologic valgus is spontaneous improvement between four and seven years of age (figure 2 and figure 3) [1]. Excessive asymmetric genu valgum also may resolve spontaneously if there are no physeal or bony abnormalities on radiographs [6].

We recommend that children younger than 10 years of age with physiologic valgus (see 'Physiologic valgus' above) be managed with observation and caregiver reassurance [5,8,10]. Patients can be followed at four- to six-month intervals to ensure resolution [9]. Bracing is ineffective, unnecessary, poorly tolerated, and may have negative psychosocial sequelae [6,19,20]. (See 'Physiologic valgus' above.)

Surgical treatment may be indicated for children older than 10 years with symptoms (eg, difficulty running, knee or foot pain) or those with significant deformity (>8 cm [approximately 3 inches] between the medial malleoli when the patellas are facing forward and the femoral condyles touching (figure 4)) [21]. Surgical treatment is usually deferred until the child is at least 10 years old to determine whether the alignment will correct spontaneously.

Surgical procedures for correction of genu valgum include guided growth through hemiepiphysiodesis (arrest of the growth plate on the apical side of the deformity) and tibial or femoral osteotomy.

Pathologic knock-knees — The management of pathologic knock-knees depends upon the underlying problem.

Posttraumatic

Posttraumatic valgus deformity (Cozen fracture) is more likely to resolve spontaneously in children younger than five years than in older children [22]. Children younger than five years can be managed with observation. Older children, and children whose deformities do not fully correct spontaneously, may benefit from surgical correction with hemiepiphysiodesis (arrest of the growth plate on the apical side of the deformity) [23].

Posttraumatic valgus deformity resulting from a distal femoral or proximal tibial physeal fracture and subsequent growth arrest typically does not resolve spontaneously. Such deformities may worsen over time as the patient grows. Worsening or symptomatic deformity may be treated with physeal bar excision or corrective osteotomy.

Systemic conditions – Once a diagnosis is made, medical therapy for the primary disease should be optimized (if effective medical therapy is available) [10]. Medical management may result in some improvement in lower-extremity alignment.

Surgical treatment should be reserved for patients with residual deformity after medical optimization [9]. Surgical treatment for pathologic knock-knees may include guided growth by performing hemiepiphysiodesis (arrest of the growth plate on the apical side of the deformity) or tibial or femoral osteotomy.

OUTCOME — The natural history of physiologic valgus is spontaneous improvement between four and seven years of age (figure 2 and figure 3).

Pathologic genu valgum can affect knee function, leading to abnormal tracking of the patella, increased load on the lateral compartment of the knee, and stress on the medial collateral ligament [24]. Long-term sequelae may include meniscal tears (medial, lateral, or both), patellofemoral pain or subluxation, and increased risk of osteoarthritis.

SUMMARY AND RECOMMENDATIONS

Normal physiologic alignment – Lower-extremity alignment goes through a predictable progression from varus (bow-legs) to valgus (knock-knees) over the first seven years of life (figure 2 and figure 3). (See 'Normal physiologic alignment' above.)

Causes of knock-knees

Physiologic valgus – Most young children with knock-knees have physiologic valgus. Physiologic valgus is defined by a tibiofemoral angle within two standard deviations of the mean for age. Characteristic features of physiologic valgus include age between two and five years, symmetric valgus, normal stature, and lack of symptoms. (See 'Physiologic valgus' above.)

Pathologic valgus – Pathologic causes of knock-knees in children include posttraumatic (eg, Cozen fracture, distal femoral or proximal tibial physeal fractures), rickets, skeletal dysplasia, mucopolysaccharidosis, and neoplasms (table 1) [4]. Clinical features suggestive of pathologic valgus are listed in the table (table 2). (See 'Pathologic valgus' above.)

Imaging – We suggest that radiographs be obtained in children with clinical features suggestive of pathologic valgus (table 2). Radiographs should include both legs from the hips to the feet, with the child standing and the patellas pointing straight ahead (image 3). (See 'Radiographs' above.)

Indications for referral – We suggest that children with clinical features suggestive of pathologic valgus (table 2) be referred to an orthopedic surgeon and/or other specialist as indicated by the suspected underlying condition (eg, nephrologist, endocrinologist, geneticist, rheumatologist). (See 'Indications for referral' above.)

Management

Physiologic valgus – The natural history of physiologic knock-knees is spontaneous improvement between age four and seven years. We manage children younger than 10 years with physiologic valgus with observation and caregiver reassurance. Orthotics (braces, splints, shoe inserts) are ineffective and unnecessary, and may have negative psychosocial sequelae. (See 'Physiologic valgus' above and 'Physiologic knock-knees' above.)

Pathologic valgus – The management of pathologic valgus depends upon the underlying problem. Medical therapy for the primary disease should be optimized (if effective medical therapy is available). Surgical treatment should be reserved for patients with residual deformity after medical optimization. (See 'Pathologic valgus' above.)

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