Pediatric Genu Varum Workup

Updated: Nov 14, 2019
  • Author: Peter M Stevens, MD; Chief Editor: Jeffrey D Thomson, MD  more...
  • Print
Workup

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. [8] In a select few patients, bone densitometry studies may be warranted.

Next:

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 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.

Previous
Next:

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.

Previous
Next:

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. [9]

Previous