Orthopaedic Surgery - Genu Valgum (Knock-Knee)

Basics

Genu valgum, commonly called knock-knee, describes a lower-extremity alignment in which the knees angle toward one another while the ankles remain separated.

A degree of genu valgum is a normal developmental finding in young children, particularly between approximately 2 and 4 years of age.

Normal Development

Girls normally demonstrate slightly more physiologic valgus than boys.

As growth continues, the valgus gradually decreases, and the lower extremities usually approach the typical adult alignment by approximately 6–7 years of age.

Pathologic Genu Valgum

Persistent or excessive valgus may result from disorders such as rickets, previous trauma, skeletal dysplasia, or genetic abnormalities.

Some children have persistent idiopathic genu valgum without an identifiable underlying disorder.

When substantial valgus persists beyond approximately 7 years of age, it is less likely to represent normal physiologic development.

Anatomic Location

The deformity most commonly arises from altered growth around the knee, particularly involving the distal femoral and proximal tibial physes.

The deformity may originate from the femur, tibia, or both.

Epidemiology

Pathologic genu valgum is uncommon.

The reported incidence is less than approximately 1 per 1,000 children.

Age

Patients requiring evaluation commonly present between approximately 3 and 11 years of age.

Physiologic valgus is most apparent in early childhood.

Sex

Physiologic genu valgum is somewhat more pronounced and more commonly noticed in females than males.

Risk Factors

A family history of genu valgum may increase the likelihood of persistent idiopathic deformity.

Proximal Tibial Metaphyseal Fracture

A proximal tibial metaphyseal fracture in a child, sometimes referred to as a Cozen fracture, can be followed by asymmetric overgrowth and progressive valgus deformity.

Parents should be informed of this possibility, even when the initial fracture heals uneventfully.

Genetics

Several metabolic and skeletal disorders associated with genu valgum have an inherited basis.

Certain forms of rickets are genetic, and idiopathic valgus alignment may also cluster within families.

Etiology

Potential causes include physiologic development, metabolic disease, steroid-related skeletal effects, post-traumatic growth disturbance, skeletal dysplasia, and chromosomal disorders.

Physiologic Genu Valgum

Physiologic genu valgum represents a normal stage of lower-extremity development and generally corrects spontaneously with growth.

Metabolic Disease

Rickets and renal osteodystrophy may weaken the metaphyseal bone and disturb physeal growth, resulting in progressive angular deformity.

Post-Traumatic Deformity

A proximal tibial fracture may lead to asymmetric growth and delayed valgus deformity.

The deformity can appear months after the original injury.

Skeletal Dysplasia

Conditions such as pseudoachondroplasia and metaphyseal dysplasia may produce substantial valgus because of abnormal growth around the knee.

Chromosomal Disorders

Genu valgum may also occur in association with chromosomal conditions such as Klinefelter syndrome or Down syndrome.

Associated Conditions

Important associated disorders include proximal tibial fracture, pseudoachondroplasia, renal osteodystrophy, metaphyseal dysplasia, rickets, Down syndrome, and multiple osteochondromas.

Diagnosis

Signs and Symptoms

The most common reason for presentation is parental concern regarding the appearance of the child’s legs.

Most children with physiologic genu valgum have no pain or functional limitation.

Pain

Childhood genu valgum is usually painless.

Occasionally, excessive valgus may be associated with patellofemoral discomfort or altered patellar tracking.

Adult Symptoms

Persistent severe valgus in adulthood can increase loading across the lateral compartment of the knee and may contribute to lateral compartment osteoarthritis and patellofemoral symptoms.

Physical Examination

Range of Motion

Knee range of motion should be assessed and compared bilaterally.

Associated flexion contracture, hyperextension, or rotational abnormality should be documented.

Growth Assessment

Height and weight should be measured and plotted against age-appropriate growth charts.

Short stature or abnormal growth patterns may suggest skeletal dysplasia, endocrine disease, or another systemic disorder.

Femorotibial Angle

The angle between the femoral and tibial axes can be measured clinically using a goniometer.

This provides an estimate of the degree of valgus.

Intermalleolar Distance

With the patient standing and the knees touching, the distance between the medial malleoli is measured.

An increased intermalleolar distance reflects greater valgus deformity.

Adjacent Joints

The hips and ankles should also be examined because deformity or contracture at these levels may alter apparent knee alignment.

Rotational Profile

Femoral and tibial rotation should be assessed.

Rotational abnormalities may exaggerate or mask the appearance of genu valgum.

Gait

The patient’s gait should be observed for abnormal alignment, circumduction, instability, or patellar maltracking.

Ligament Examination

The medial and lateral collateral ligaments should be tested for laxity.

Ligamentous instability may contribute to apparent or progressive valgus alignment.

Laboratory Tests

Laboratory testing is unnecessary for typical physiologic genu valgum.

It is indicated when a metabolic or endocrine disorder is suspected.

Evaluation for Rickets or Metabolic Bone Disease

Potential studies include serum calcium, phosphate, alkaline phosphatase, blood urea nitrogen, creatinine, and vitamin D levels.

Vitamin D Assessment

When evaluating rickets, measurement of 25-hydroxyvitamin D is particularly useful.

Additional studies, including 1,25-dihydroxyvitamin D and renal or endocrine investigations, may be obtained depending on the suspected cause.

Hypophosphatemic Rickets

Familial hypophosphatemic rickets is an important inherited cause of progressive lower-extremity deformity.

Serum phosphate and related metabolic studies are therefore important when this condition is suspected.

Imaging

When Imaging Is Unnecessary

Routine radiographs are generally unnecessary in children younger than approximately 6 years when the genu valgum is symmetric, painless, and clearly physiologic.

Indications for Imaging

Imaging should be obtained when the deformity is asymmetric, severe, progressive, painful, persistent beyond the expected age, associated with short stature, or accompanied by suspicion of metabolic or skeletal disease.

Standing Long-Leg Radiograph

The preferred initial study is a standing AP radiograph of the entire lower extremity from hip to ankle.

The patella should face directly forward to minimize rotational error.

Femorotibial Angle

The radiograph allows measurement of the femorotibial angle and helps determine whether the deformity arises primarily from the distal femur, proximal tibia, or both.

Mechanical Axis

The mechanical axis of the lower extremity should be assessed.

In normal alignment, a line from the center of the femoral head toward the center of the ankle passes near the central portion of the knee.

Increasing lateral displacement indicates worsening genu valgum.

Differential Diagnosis

The principal diagnostic task is distinguishing physiologic valgus from pathologic valgus.

It is also important to determine whether the deformity is developmental or acquired.

Physiologic Genu Valgum

Physiologic genu valgum occurs without evidence of rickets, skeletal dysplasia, trauma, tumor, or other disease and improves spontaneously with growth.

Skeletal Dysplasia

Important skeletal dysplasias associated with valgus include metaphyseal dysplasia, pseudoachondroplasia, and multiple osteochondromas.

Developmental Causes

Developmental causes include physiologic valgus, idiopathic persistent genu valgum, and skeletal dysplasia.

Acquired Causes

Acquired causes include metabolic disease, post-traumatic growth disturbance, and neoplastic or other physeal disorders.

Treatment

Physiologic Genu Valgum

No treatment is required for physiologic genu valgum in children younger than approximately 7 years of age when the deformity is symmetric and within normal developmental limits.

Reassurance and observation are usually sufficient.

Persistent Idiopathic Genu Valgum

If substantial deformity persists beyond approximately 7 years of age, continued observation may be appropriate until the child approaches an age at which guided growth could be considered.

Surgical treatment is generally reserved for persistent, progressive, or symptomatic deformity.

Pathologic Valgus

The underlying disorder should be addressed before or together with correction of the angular deformity.

Metabolic Disease

In patients with renal osteodystrophy, rickets, or another metabolic condition, medical control of the underlying disease is essential.

Management often requires coordination with an endocrinologist or nephrologist.

Bracing

Bracing has not been shown to reliably correct or prevent progression of structural genu valgum.

Osteotomy

Severe deformity associated with skeletal dysplasia or metabolic disease may require one or more corrective osteotomies once the underlying disease has been adequately controlled.

Post-Traumatic Valgus

Children with proximal tibial metaphyseal fractures should be followed for several years because valgus deformity can develop after apparent fracture healing.

Early Osteotomy

Early corrective tibial osteotomy is generally avoided because post-traumatic valgus may spontaneously improve and early osteotomy has historically been associated with recurrence.

Persistent Deformity

If unacceptable valgus remains after approximately 1–2 years of observation, guided growth or corrective osteotomy may be considered depending on remaining growth and severity.

Skeletal Dysplasia

Children with pseudoachondroplasia or metaphyseal dysplasia may develop progressive valgus.

Corrective osteotomy or guided growth may be required when the deformity becomes substantial or symptomatic.

Activity

No routine activity restrictions are required for physiologic genu valgum.

Children may participate in normal play and sports unless another underlying disorder requires limitation.

Physical Therapy

Physical therapy does not alter physeal growth or correct structural genu valgum.

Exercises therefore do not change the natural history of the deformity.

Therapy may still be useful for associated weakness or postoperative rehabilitation.

Surgery

The two principal surgical strategies are hemiepiphysiodesis and corrective varus osteotomy.

Hemiepiphysiodesis

Hemiepiphysiodesis is a guided-growth procedure used in skeletally immature children with sufficient growth remaining.

Principle

Growth on the medial side of the distal femoral or proximal tibial physis is temporarily slowed, allowing continued growth on the lateral side to gradually correct the valgus.

Techniques

Guided growth may be achieved using staples, transphyseal screws, or plate-and-screw tension-band devices.

Indications

Hemiepiphysiodesis may be considered when the mechanical axis passes markedly lateral to the knee, particularly into the lateral-most zones of the tibial plateau.

Pain combined with significant mechanical-axis deviation may also support intervention.

Advantages

The procedure is relatively minimally invasive, does not substantially weaken the bone, and usually allows early weight bearing.

Goal

The objective is to achieve satisfactory mechanical alignment by the time skeletal growth is completed.

Careful timing and follow-up are necessary to avoid overcorrection.

Corrective Osteotomy

Osteotomy is preferred when immediate correction is required or insufficient growth remains for guided growth to work effectively.

Procedure

The involved bone is divided, realigned into a more neutral or varus position, and stabilized with internal fixation.

The osteotomy may be performed at the distal femur, proximal tibia, or both depending on the site of deformity.

Recovery

Recovery is more demanding than after hemiepiphysiodesis because the bone is completely divided and must heal before unrestricted activity.

Surgical Success

Appropriately selected surgical correction has an overall success rate greater than approximately 90%.

Follow-Up

Prognosis

Physiologic genu valgum has an excellent prognosis and usually resolves as growth continues.

Mild deformity, particularly valgus less than approximately 15°, often improves by approximately 7–10 years of age when no metabolic or skeletal disorder is present.

Complications of Untreated Genu Valgum

Severe persistent valgus may cause patellofemoral pain, abnormal patellar tracking, gait disturbance, and increased loading of the lateral compartment of the knee.

Over many years, this can contribute to degenerative arthritis.

Surgical Complications

Potential complications include infection, compartment syndrome, neurovascular injury, recurrent deformity, and overcorrection into genu varum.

Guided-growth procedures additionally require careful monitoring to prevent excessive correction.

Patient Monitoring

Children with idiopathic genu valgum can generally be followed at approximately 12–24-month intervals while spontaneous improvement is expected.

Follow-up should document intermalleolar distance, femorotibial angle, gait, mechanical-axis alignment, symmetry, pain, growth, and progression or improvement of the deformity.