There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
X-ray Options for Leg Length Discrepancy
- Full-length standing anteroposterior radiograph: This method is supported by several studies as a reliable and comprehensive approach for measuring limb length discrepancy 1, 2, 3.
- Scanogram: Although commonly used, scanograms have potential pitfalls and may not provide as accurate measurements as full-length standing anteroposterior radiographs 1, 2, 3.
- Pelvic radiograph: This method may not be sufficient for assessing leg length discrepancy, especially in total hip arthroplasty patients, as it does not capture all potential sources of discrepancy 4.
- EOS radiology: This is a long-limb radiology method that can provide a more reproducible and holistic measurement of leg length discrepancy, especially when using ASIS-to-ankle measurements 4.
Comparison of X-ray Methods
- Full-length standing anteroposterior radiograph vs. scanogram: Studies have shown that the measurements obtained from these two methods are highly correlated, but the full-length standing anteroposterior radiograph may be more reliable and comprehensive 1, 2.
- Weight-bearing vs. supine imaging: Research suggests that there is no significant difference in leg length discrepancy measurements between weight-bearing and supine radiographs 5.
- Pelvic radiograph vs. EOS radiology: The conventional pelvic radiograph measurement of leg length discrepancy does not correlate well with long leg measurements and may not provide a true appreciation of discrepancy 4.