Measurement of femoral neck anteversion in 3D. Part 1: 3D imaging method

Abstract

Femoral neck anteversion is the torsion of the femoral head with reference to the distal femur. Conventional methods that use cross-sectional computed tomography (CT), magnetic resonance or ultrasound images to estimate femoral anteversion have met with several problems owing to the complex, three-dimensional (3D) structure of the femur. These problems include not only the difficulty of defining the direction of the femoral neck axis and condylar line but also the dependency upon patient positioning. In particular, the femoral neck axis, the direction of the femoral head, known as the major source of error, is difficult to determine from either a single or several two-dimensional (2D) cross-sectional images. A new method has been devised for the measurement of femoral anteversion using the 3D imaging technique. 3D reconstructed CT images from the femoral head and trochanter to the distal femur are used to measure the anteversion. It is necessary to remove the soft tissue from the CT images and extract just the bone part. Then, the femoral anteversion is measured from a computer-rendered femur image. The 3D imaging method is compared with both the conventional 2D method and the physical method using 20 dried femurs. For the physical method, which is used as a reference value, a special apparatus is devised. The average difference between the results of the physical method and those of the 2D CT method is 5.33 degrees. The average difference between the results of the physical method and those of the 3D imaging method is 0.45 degrees. Seventy-four patients, who suffer from toe-in-gait disease, are tested to compare the 3D imaging method with the conventional 2D CT method. The average difference between the 2D and 3D methods is 8.6 degrees, and the standard is 7.43 degrees. This method provides a very accurate and reliable measurement of femoral anteversion, as it is virtually equivalent to the direct measurement of bisected dried femur in vitro.

CORR Insights®: Can Femoral Rotation Be Localized and Quantified Using Standard CT Measures?

“…In contrast to previous reports [7,11], the accuracy of all three techniques, including the traditional single neck axis cut, was equally high with a deviation from the true torsion of only 1 ± 4 degrees. Previously published studies [1,9] have questioned the influence of the bony anatomical torsional deformity on the resulting gait pattern.…”

“…Many articles focus on the accuracy and reliability of CT measurements; these show that the localization and level of the CT cuts on the distal and especially on the proximal femur appear to influence the accuracy of the measurements made [7,8,11]. Proximal femoral anatomy introduces bias when taking measurements from a simple transverse plane cut.…”

“…Proximal femoral anatomy introduces bias when taking measurements from a simple transverse plane cut. Therefore, techniques have been proposed to incline the plane and to reconstruct the intertrochanteric and neck region using three-dimensional CT [7,11].…”

Determinants of Hip Displacement in Children With Cerebral Palsy

“…Another problem is that measurement of femoral deformities, as seen on radiographs, could be affected by profound contracture and malposture in children with cerebral palsy who are nonambulatory [8,16]. With advancements in computerized image processing techniques, three-dimensional (3-D) CT has been proposed as a superior method to measure femoral deformities in children with cerebral palsy [1,4,7,11,13,18,23,32,34,35]. Davids et al [11] reported the accuracy of measuring femoral anteversion was significantly compromised when the femoral models were placed in cerebral palsy alignment (flexion, adduction, and internal rotation), and 3-D assessment was significantly better than two-dimensional assessment.…”

Total Hip Replacement in Developmental Dysplasia of the Hip: Pitfalls and Challenges

“…Lateral views of the hip and Judet views can be helpful to determine the acetabular bone stock. CT scan can be useful to evaluate acetabular bone stock and femoral version [8].…”