Genu Valgum, Pediatrics 

Genu valgum is the Latin-derived term used to describe knock-knee deformity. While many otherwise healthy children have knock-knee deformity as a passing trait, some individuals retain or develop this deformity as a result of hereditary or genetic disorders or metabolic bone disease. The typical gait pattern is circumduction, requiring that the individual swing each leg outward while walking in order to take a step without striking the planted limb with the moving limb. Not only are the mechanics of gait compromised but also, with significant angular deformity, anterior and medial knee pain are common. These symptoms reflect the pathologic strain on the knee and its patellofemoral extensor mechanism.

For persistent genu valgum, treatment recommendations have included a wide array of options, ranging from lifestyle restriction and nonsteroidal anti-inflammatory drugs to bracing, exercise programs, and physical therapy. In recalcitrant cases, surgery may be advised. No consensus exists regarding the optimal treatment. Some surgeons focus (perhaps inappropriately) on the patella itself, favoring arthroscopic or open realignment techniques. However, if valgus malalignment of the extremity is significant, corrective osteotomy or, in the skeletally immature patient, hemiepiphysiodesis may be indicated.

Osteotomy indications and techniques have been well described in standard textbooks and orthopedic journals and are not the focus of this article. Hemiepiphysiodesis can be accomplished using the classic Phemister bone block technique, the percutaneous method, hemiphyseal stapling, or, more recently, application of a single 2-hole plate and screws around the physis. The senior author, having experience in each of these techniques, has developed the later technique in order to solve 2 of the problems sometimes encountered with staples, namely hardware fatigue and migration. The rationale and versatility of this technique for managing genu valgum are the emphasis of this article.

Images of genu valgum and its treatment are provided below:

Recent studies

Wiemann et al compared the use of the 8-plate for hemiepiphysiodesis with that of physeal stapling in 63 cases of angular deformity in lower extremities between 2000 and 2007, with 39 limbs undergoing staple hemiepiphysiodesis and 24 undergoing 8-plate hemiepiphysiodesis. The authors found the 8-plate to be as effective as staple hemiepiphysiodesis in terms of the rate of correction (approximately 10º/y, P=0.48) and complications (12.8% vs. 12.5%, P=1.0). However, patients with abnormal physes (eg, Blount disease, skeletal dysplasias) did have a higher rate of complications (27.8% vs. 6.7% for patients with normal physes, P=0.04), but there was no difference between the 8-plate group and the staple group.^[1]

Koshino performed a follow-up study (10-38 y) of 57 knees in 45 patients (age 42-73 y at follow-up) who underwent corrective osteotomy for knee deformities. Supracondylar femoral osteotomy had been performed on 12 knees (11 patients), high tibial osteotomy above the tibial tuberosity on 8 knees (6 patients), and below the tuberosity on 37 knees (28 patients). The deformities at final follow-up had satisfactorily corrected, except in 9 cases. A subsequent total knee arthroplasty had been necessary in 2 knees, and 7 patients experienced dull pain after strenuous activity, with osteophytes present radiographically.^[2]

The focus of this article is the indications, techniques, complications, and outcome of guided growth using the reversible plate technique for the correction of pathologic genu valgum. Since the introduction of staples by Walter Blount in 1949, this procedure has waxed and waned in popularity and remains the subject of criticism and controversy. Indeed, some recent review articles and book chapters dismiss stapling as a historical procedure, citing unpredictability and the fear of permanent physeal arrest as results of stapling. While stapling can work well, occasional breakage or migration of staples can necessitate revision of hardware or premature abandonment of this method of treatment.

Some surgeons have reverted to osteotomy of the femur and/or tibia-fibula as the definitive means of addressing genu valgum. However, this is a very invasive method fraught with potential complications, including malunion, delayed healing, infection, neurovascular compromise, and compartment syndrome. Further complicating the picture, these deformities are often bilateral, requiring a staged correction. The aggregate hospitalization, recovery time, costs, and risks make osteotomy a last resort for angular corrections (unless the physis has already closed).

Percutaneous drilling or curettage of a portion of the physis yields only a small scar and no implant is required. However, this is a permanent, irreversible technique. Therefore, its use is necessarily restricted to adolescent patients and is predicated upon precise timing of intervention, requiring close follow-up to avoid undercorrection or (worse yet) overcorrection.

Some authorities advocate using percutaneous epiphyseal transcutaneous screws as a means of achieving angular correction.^{[3, 4]} While this is performed through a small incision, the physis is violated and the potential exists for the formation of an unwanted physeal bar, with its sequelae. To date, its no potential for reversing the procedure has been documented; therefore, the only reported cases have been in adolescents.

By comparison, guided growth, using a nonlocking 2-hole plate and screws, is a reversible and minimally invasive outpatient procedure, allowing multiple and bilateral simultaneous deformity correction. A single implant (Orthofix 8-plate) is used per physis, as shown in the images below; this serves as a tension band, allowing gradual correction with growth. Because the focal hinge of correction is at or near the level of deformity, compensatory and unnecessary translational deformities are avoided.^{[5, 6]}

The previous empirical constraints related to the indications, including appropriate age group and the etiology of deformity, have been challenged successfully using this technique, with consistently good results. In a personal series of more than 100 patients, ranging in age from 19 months to 17 years, and some with pan-genu deformities, the senior author has not had a permanent physeal closure.

Normal alignment means that the lower extremity lengths are equal and the mechanical axis (center of gravity) bisects the knee when the patient is standing erect with the patellae facing forward. This position places relatively balanced forces on the medial and lateral compartments of the knee and on the collateral ligaments, while the patella remains stable and centered in the femoral sulcus.

In children younger than 6 years, physiologic genu valgum is common but is self-limiting and innocuous. In children (of any age) with pathologic valgus, when the mechanical axis deviates into or beyond the lateral compartment of the knee, regardless of the etiology, a number of clinical problems may ensue. Medial ligamentous strain may be associated with recurrent knee pain. The patellofemoral joint may become shallow, incongruous, or unstable, causing activity-related anterior knee pain. In extreme cases, frank patellar dislocation with or without osteochondral fractures may ensue.

Because patellar dislocation reflects an insidious and progressive growth disturbance, nonoperative management relying on physical therapy and bracing is of little value. During the adult years, premature and eccentric stress on the knee may result in hypoplasia of the lateral condyle, meniscal tears, articular cartilage attrition, and arthrosis of the anterior and lateral compartments.

Frequency

Adolescent idiopathic genu valgum may be familial, or it may occur sporadically. The true incidence is unknown. Certainly, it is one of the most common causes of anterior knee pain in teenagers and is a frequent reason for orthopedic consultation. Likewise, the incidence of the predisposing syndromes is difficult to ascertain. Predisposing syndromes, such as hereditary multiple exostoses, Down syndrome, and skeletal dysplasias, are more apt to manifest in patients aged 3-10 years, and valgus may become severe if untreated. Regardless of the etiology, surgical correction of significant and symptomatic malalignment is warranted, regardless of the age of the patient.

In countries where malnutrition is common and access to medical care is limited, the overall incidence of genu valgum is undoubtedly higher. While polio has been largely eradicated, other infectious diseases and mistreated (or untreated) traumatic injuries make physeal damage a frequent cause of progressive and disabling clinical deformity. Likewise, untreated congenital anomalies, genetic disorders, rheumatologic diseases, and hemophilia may cause genu valgum.

The fact that toddlers aged 2-6 years may have physiologic genu valgum is well recognized. For this age group, typical features include ligamentous laxity, symmetry, and lack of pain or functional limitations. Despite the sometimes-impressive deformities, no treatment is warranted for this self-limiting condition. Bracing is meddlesome and expensive, and shoe modifications are unwarranted. The natural history of this condition is benign; therefore, parents simply need to be educated as to what to expect and when. Annual follow-up until resolution may help to assuage their fears.

In contrast, adolescent idiopathic genu valgum is not benign or self-limiting. Teenagers may present with a circumduction gait, anterior knee pain, and, occasionally, patellofemoral instability. The natural history of this condition may culminate in premature degenerative changes in the patellofemoral joint and in the lateral compartment of the knee. Various other conditions, including postaxial limb deficiencies, genetic disorders such as Down syndrome, hereditary multiple exostoses, neurofibromatosis, and vitamin D–resistant rickets may cause persistent and symptomatic genu valgum. Some of these conditions require team management with other health care providers; however, surgical intervention is still likely to be necessary to correct the malalignment of the knees.

With normal alignment, the physes and epiphyses are shielded from pathologic stress, and balanced growth preserves straight legs and normal function. In genu valgum, as the mechanical axis shifts laterally, pathological stress is placed on the lateral femur and tibia, inhibiting growth and possibly leading to a vicious cycle. Not only is physeal growth inhibited, but also the Hueter-Volkmann effect upon the entire epiphysis prevents its normal expansion. According to the Hueter-Volkmann principle, continuous or excessive compressive forces upon the epiphysis have an inhibitory effect upon growth. Consequently, growth in the lateral condyle of the femur is suppressed globally, resulting in a shallow femoral sulcus and a propensity for the patella to tilt and subluxate laterally.

During gait, medial thrust of the tibia relative to the femur may compromise the integrity of the restraining medial collateral ligaments, resulting in localized pain and progressive joint laxity.

In addition to knee pain and laxity, patients may develop a circumduction gait, swinging each leg outward to avoid knocking their knees together. This gait pattern is awkward and laborious; the patient is unable to run, ride a bicycle, or participate safely and effectively in play or sports activities, potentially leading to social isolation and possible ridicule. Left untreated, the natural history for this condition is likely to be that of inexorable progression and deterioration.

The lifelong valgus knee presents a daunting challenge to the adult reconstructive orthopedist. Total knee arthroplasty may be fraught with complications, including persistent malalignment, neurovascular compromise, patellar instability, and premature loosening of the prosthetic components. Therefore, it is in the best interest of the patient for the clinician to try to prevent such an outcome. Correction of genu valgum and neutralization of the forces across the knee are the goals of early and, if necessary, repeated intervention, which forestalls the need for more invasive adult reconstructive procedures.

The history of the deformity is important to ascertain and document. On rare occasions, genu valgum may be noted in the nursery, indicating the presence of some type of localized or generalized skeletal malformation or dysplasia. Congenital lateral dislocation of the patella has been described. The extensor mechanism of the knee is displaced laterally so that every time the child contracts the quadriceps, the knee is flexed (rather than extended) and rotates outward, accentuating the valgus deformity. More commonly, genu valgum does not become apparent until after the child reaches walking age. A normal variant of the disorder in toddlers (physiologic valgus) typically is symmetrical and pain free, but it should resolve spontaneously by the time the child is aged 6 years. If the valgus is unilateral or symptomatic, referral to an orthopedist and radiographic evaluation are warranted.

Family history may be important because certain heritable conditions, such as hereditary multiple exostoses, Marfan syndrome, osteogenesis imperfecta, or vitamin D–resistant rickets may predispose a patient to this condition.

The physical examination should include assessment of the gait pattern, including the propensity for circumduction, and evaluation of lower extremity lengths. Stature, craniofacial features, the spine, and the upper extremities should be evaluated. Various genetic conditions and skeletal dysplasias may be documented in this manner; consultation with a geneticist may be warranted.

With the child standing, compare the relative limb lengths by leveling the pelvis with blocks and measuring and recording the intermalleolar distance (IMD). Torsional deformities of the femur and/or tibia should be documented. Often, genu valgum is observed in association with outward torsion of the femur, tibia, or both. Look for retropatellar crepitus and tenderness and note patellar tilt, tracking, and stability. For situations other than the aforementioned physiologic genu valgum, medical imaging is warranted.

Physiologic genu valgum should be treated expectantly. The family should be educated to avert unnecessary concerns and inappropriate treatment. Bracing and corrective shoes are ineffective, and physical therapy is of no benefit. Pathologic genu valgum warrants aggressive treatment to alleviate symptoms and prevent progression. Bracing and therapy are inadequate to meet these goals. Surgical intervention is the only successful intervention for correcting the problem. Surgical options include osteotomy or growth manipulation (hemiepiphysiodesis).

The radiographic parameters relevant to defining genu valgum are best measured on a full length, standing, anteroposterior (AP) radiograph of the legs. The angle is measured between the femoral shaft and its condyles (the normal angle is 84°); this is referred to as the lateral distal femoral angle. The other relevant angle is the proximal medial tibial angle; this is the angle between the tibial shaft and its plateaus (the normal angle is 87°). The mechanical axis is a straight line drawn from the center of the femoral head to the center of the ankle; this should bisect the knee. Allowing for variations of normal, an axis within the 2 central quadrants of the knee is deemed acceptable.

Physeal closure, whether it be due to local trauma or to maturity, is the sole contraindication to using guided growth for deformity correction. Obviously, this technique cannot be used after skeletal maturity, when the only option is a corrective osteotomy. In some cases, malrotation actually improves or is resolved as the mechanical axis is restored to neutral; therefore, rotational osteotomies may be reserved for patients who are still troubled by unresolved malrotation. Likewise, lengthening (along the anatomic axis) may be reserved for children who ultimately require limb length equalization.