Laboratory Studies
When an underlying syndrome is suggested by the physical findings and history, consultation with a geneticist and an appropriate workup are warranted. If metabolic bone problems are a concern, relevant hematologic and urine studies are warranted, along with consultation with an endocrinologist. Serum alkaline phosphatase (ALP) level has been associated with genu varum regardless of the presence of radiographic abnormalities in the growth plate. [10] ALP level may be a useful measurement in children with genu varum resulting from vitamin D deficiency. [11] In a select few patients, bone densitometry studies may be warranted.
Radiography
In most cases, plain radiography is the only diagnostic procedure required. The gold standard of radiographic documentation is the full-length weightbearing anteroposterior (AP) view of the lower extremities, taken with the patellae facing forward. In addition to the knee deformities, there may be varus of the proximal femur or the distal tibia or fibula.
The relevant anatomy, in addition to possible hip and ankle deformities, includes the distal femoral and proximal tibial physes, either or both of which may contribute to varus malalignment. A simple screening test is to view the full-length AP radiograph with the knee in a horizontal plane. When the film is oriented so that the knee is on a horizontal plane, it may be readily apparent whether the femur, tibia, or both are contributing to the deformity and therefore which level or levels should be addressed.
The best way of measuring and determining which physes are contributing to deformity is to measure the anatomic joint-shaft angles at each level. These include the lateral distal femoral angle (LDFA), which is normally 84°, and the proximal medial tibial angle (PMTA), which is normally 87° (see the image below).
Anatomic angles are measured between joint surface of each bone and its respective shaft. Lateral distal femoral angle (LDFA) is normally 84°, and proximal medial tibial angle (MPTA) is 87°. On close-up view, one can measure joint convergence angle (normally 0°); this is defined by articular surface lines of femur and tibia. Lateral ligamentous laxity can contribute to varus malalignment.
In addition, when the lateral ligaments are incompetent, measuring the joint convergence angle or obtaining a varus stress AP radiograph may demonstrate their respective contributions to the clinical deformity. It is important to remember that there may be sagittal-plane and rotational deformities that confound the analysis and treatment.
In contradistinction, scanograms are of questionable value because they are not weightbearing, do not demonstrate diaphyseal deformities, and do not show the mechanical axis.
Other Tests
Aside from a well-documented clinical examination and gait observation (repeated as necessary to document progression) and the standard radiographs already mentioned, other tests generally are not indicated. Unless a physeal bar is suspected (which is unusual), there is no need to resort to computed tomography (CT) or magnetic resonance imaging (MRI).
In select cases, gait analysis may be interesting, but it will not determine either the need for or the timing of intervention.
Histologic Findings
Depending upon the underlying etiology of genu varum, epiphyseal, physeal, or metaphyseal histologic abnormalities may be present, and bone density may be diminished. However, biopsy of the bone is rarely necessary or helpful. Such invasive procedures may have an adverse effect upon physeal growth and the outcome of treatment. [12]
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Mechanical axis is measured on full-length weightbearing radiograph by drawing line from center of femoral head to center of ankle. Normally, it should bisect knee, with joint horizontal and parallel to ground. Genu varum is defined by medial displacement of mechanical axis. Shown here is tibia vara and slight lateral ligamentous laxity contributing to deformity.
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Three factors contributing to genu varum: femur varum, ligamentous laxity, and tibia vara. Mechanical axis is further deviated medially.
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If knee is divided into quadrants and variations of normal allowed for, mechanical axis should be neutral or at least fall within medial or lateral zone 1. Deviation into zone 2 is relative indication for surgical intervention, and zone 3 is obvious call for action. If physes are open, correction may be gained by guided growth; after skeletal maturity, only choice is corrective osteotomy.
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Anatomic angles are measured between joint surface of each bone and its respective shaft. Lateral distal femoral angle (LDFA) is normally 84°, and proximal medial tibial angle (MPTA) is 87°. On close-up view, one can measure joint convergence angle (normally 0°); this is defined by articular surface lines of femur and tibia. Lateral ligamentous laxity can contribute to varus malalignment.
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Tibia vara (Blount disease) is growth disturbance of proximal medial tibia that can present any time from infancy to adolescence. Natural history is one of inexorable progression, premature closure of upper medial tibial physis, lateral thrust, ligamentous laxity, and, ultimately, joint instability and degeneration. At age 5, guided growth would have been sufficient. After physeal closure, complex osteotomies are required.
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Hypophosphatemic rickets is disturbance in vitamin D metabolism that weakens physes through delayed ossification. Consequent deformities may progress despite careful medical management and bracing. Deformities are typically bilateral, involving both femur and tibia.
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Child wore her braces religiously, only to experience steady progression of deformities.
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At 2 years after guided growth of distal lateral femora and proximal lateral tibiae (and without further bracing), patient's legs are straight. She will be monitored as she continues to grow.
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This 7-year-old boy with Ollier disease presented with complex deformity including varus and outward torsional deformity of right tibia and progressive limb length discrepancy. Whereas guided growth could improve varus, it could not address other two issues. Therefore, he underwent osteotomy and callotasis with Taylor Spatial Frame.
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External fixator in place.
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This 4-year-old girl with Job syndrome, which includes immunoglobulin deficiency, had osteopenia and developed pathologic fracture of proximal tibia. She then drifted into progressive genu varum. It was felt that guided growth might not work in mechanically compromised environment.
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Patient underwent corrective osteotomy of upper tibia and fibula, supplemented with cast.
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Follow-up at age 10.
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Follow-up at age 12.
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At age 5, this boy presented with asymmetrical tibia vara (Blount disease). Treating surgeon employed guided growth on right and osteotomy of tibia/fibula on left.
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At 14-month follow-up, mechanical axis is neutral on right, and plate was removed. Mechanical axis was in medial zone 2; this was addressed by insertion of lateral eight-Plate.
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After additional 8 months of guided growth, leg straightened out, and plate was removed. Patient's limb lengths remain equal, and there has been no recurrence of angular deformity. Annual monitoring will continue until maturity: if there is any drift of mechanical axis, guided growth will be repeated.
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At 1 year after proximal tibial stapling to correct limb length inequality, this scanogram shows loosening of lateral staples with consequent iatrogenic varus of tibia. Physes are still open.
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Full-length view shows mechanical axis deviation into medial zone 2; this was not demonstrable on scanogram. Staples were removed and lateral ones replaced with eight-Plate.
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At 1 year after guided growth with eight-Plate, mechanical axis has been restored to neutral. At that time, eight-Plates were employed to accomplish pan-genu epiphysiodesis to correct patient's residual limb length inequality.
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This 20-month-old boy presented with waddling gait and hip pain. His father has same condition and had osteotomies of his tibias, femora, and hips during childhood. He anticipated similar treatment for his son.
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Standing anteroposterior (AP) radiograph demonstrates varus deformities at hips, knees, and ankles, with mechanical axis in medial zone 3 bilaterally. Traditional treatment would have included staged osteotomies of proximal and distal femora and of proximal and distal tibiae and fibulae, requiring x number of casts and hospitalizations.
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Presenting AIR (abduction, inward rotation) view of pelvis shows "triangular defect," which is essentially stress fracture, of each femoral neck. This would explain his hip pain and Trendelenburg gait.
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Sequential radiographs demonstrate neutralization of mechanical axis during 13 months following guided growth. This was performed as outpatient procedure, requiring no immobilization.
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Upon removal of pan-genu eight-Plates (2/07), additional plates were applied to greater trochanter in hope of gradually increasing neck-shaft angle and obviating need for proximal femoral osteotomies.
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Clinical photographs taken at age 20 months and at age 2 years 9 months.
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Whereas complication rate of guided growth with eight-Plates remains low, there have been isolated cases of broken screws. Each broken screw has been distal (metaphyseal) screw in heavy-set patient with Blount disease. Potential solutions are to insert solid 4.5-mm screw or to add second eight-Plate.
