Femoral anteversion describes the forward twist of the femur, the thigh bone, relative to the knee’s transcondylar axis. This angle measures the natural torsion within the bone, influencing hip joint function and overall lower limb alignment. Accurate measurement is important for identifying orthopedic conditions and guiding appropriate treatment strategies.
Physical Examination Methods
Physical examination methods offer a preliminary estimation of femoral anteversion. Craig’s Test is a commonly used clinical assessment. This test involves positioning the patient face down with the knee bent to 90 degrees. The examiner rotates the hip while feeling for the point where the greater trochanter is most prominent laterally.
At this point, the femoral neck is considered parallel with the examination table. The angle of the lower leg is then measured to estimate the anteversion angle. These tests provide an estimation rather than a precise measurement. Their subjective results can vary between examiners, making them useful as a screening tool.
Imaging Modalities
Precise measurement of femoral anteversion relies on advanced imaging techniques. These modalities provide detailed anatomical views for accurate assessment of the angle between the femoral neck and the distal femoral condyles.
Computed Tomography (CT) Scan
Computed Tomography (CT) scans are an accurate method for measuring femoral anteversion. Measurement involves identifying specific anatomical landmarks on axial images. One line is drawn along the femoral neck axis at the hip, and another connects the posterior aspects of the femoral condyles at the knee (transepicondylar axis). The angle between these lines represents the femoral anteversion.
CT offers precision and reproducibility due to its clear visualization of bony structures. A consideration with CT scans is patient exposure to ionizing radiation. Despite this, CT remains a preferred method when accurate measurements are needed for surgical planning or complex cases.
Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging (MRI) provides an alternative for measuring femoral anteversion without ionizing radiation. Axial MRI sequences identify the femoral neck axis and the transepicondylar axis of the distal femur.
MRI is useful in younger patients or when repeated measurements are necessary. While effective, MRI may present challenges in image quality or resolution for certain bony landmarks compared to CT, potentially affecting measurement consistency. MRI shows a strong correlation with CT measurements, though absolute values can differ.
Conventional Radiography (X-ray)
Conventional radiography is not suitable for direct measurement of femoral anteversion. X-rays produce two-dimensional images, making it challenging to accurately assess a three-dimensional rotational alignment. They lack the necessary detail and cross-sectional views to reliably quantify the femoral anteversion angle. For accurate rotational assessments, cross-sectional imaging modalities like CT or MRI are necessary.
Understanding Measurement Results
Interpreting femoral anteversion measurements involves understanding typical ranges and their clinical implications. The “normal” anteversion angle changes with age. At birth, it averages 30 to 40 degrees, gradually decreasing as a child grows. By skeletal maturity, the average anteversion ranges between 8 and 15 degrees.
Angles outside these ranges have clinical implications. Increased anteversion, defined as an angle greater than 15 degrees, is often associated with an in-toeing gait. This increased forward twist can contribute to hip instability and issues like patellofemoral maltracking. Individuals with increased anteversion may exhibit greater internal hip rotation and reduced external hip rotation.
Conversely, decreased anteversion occurs when the angle is less than 8 degrees. This condition can lead to an out-toeing gait. Retroversion may also play a role in certain hip pathologies, such as cam-type femoroacetabular impingement. Understanding these measurements helps healthcare professionals diagnose conditions and develop management plans.