From the Research
For leg length discrepancy assessment, a standing anteroposterior (AP) radiograph of both lower extremities, known as a scanogram or orthoroentgenogram, is the recommended imaging study. This X-ray captures both legs in their entirety on a single long film while the patient stands bearing weight, allowing for accurate measurement of the femur, tibia, and total leg length. The technician will typically place a radiopaque ruler or calibration device in the image to ensure precise measurements.
Key Considerations
- For more detailed evaluation, particularly in children with growth potential, a CT scanogram may be used as it reduces radiation exposure while maintaining accuracy 1.
- MRI can also be utilized in cases where radiation exposure is a concern, though it's less common.
- These imaging studies help clinicians determine the exact location and magnitude of the discrepancy, which is crucial for treatment planning whether that involves shoe lifts for minor discrepancies (less than 2 cm) or surgical intervention for more significant differences.
- The standing position is important as it reveals functional discrepancies that might not be apparent when lying down.
Evidence Support
- A study published in 2022 found that long-limb EOS radiology can provide a more reproducible and holistic measurement of leg length discrepancy compared to conventional techniques 2.
- Another study from 2006 compared the results of full-length standing anteroposterior radiographs with scanograms and found that the measurements were very similar, especially in the absence of substantial mechanical axis deviation 1.
- More recent studies, such as one from 2023, have highlighted the importance of standardizing landmarks for measuring leg length discrepancy to ensure accurate assessments 3.
- The use of computer navigation in total hip arthroplasty has also been shown to improve the accuracy of leg length restoration, minimizing discrepancies 4.