When performing a total hip arthroplasty, it is essential to correct any pre-existing leg-length discrepancy during surgery

Abstract

Leg-length discrepancy (LLD) in individuals experiencing total hip arthroplasty (THA) is related to a substantially higher fall risk, length of post-operative hospital in-patient stay, elevated implant-related adverse events, and earlier revision. Therefore, it is essential to try to avoid LLD when implanting a THA. Several studies focus on this issue, including the following: Accelerometer-based portable navigation system, preoperative digital templating, robot-assisted surgery, the anatomical marker positioning method (shoulder-to-shoulder) and the artificial intelligence-based three-dimensional planning software system. The aforementioned methods should be familiar to surgeons who perform THA procedures, as a fundamental objective of this surgical intervention is to avoid LLD.

Key Words: Hip; Total hip arthroplasty; Leg-length discrepancy; Implant-related complications; Risk of revision

Core Tip: Leg-length discrepancies (LLDs), often greater than 5-10 mm, may result in altered gait mechanics, low-back pain, or the perception of limb inequality. These issues can directly affect patient satisfaction and functional recovery. Several advanced methods have been developed to address LLD, including accelerometer-based portable navigation system, preoperative digital templating, robot-assisted surgery, the anatomical marker positioning method (shoulder-to-shoulder) and the artificial intelligence-based three-dimensional planning system. However, it is worth noting that no technique completely eliminates the possibility of post-surgical LLD. Complex deformities, intraoperative instability, and soft-tissue imbalances can still lead to measurable discrepancies, despite the utilization of advanced tools.

TO THE EDITOR

The article recently published by Rodriguez et al[1] on leg-length discrepancy (LLD) in total hip arthroplasty (THA) referring to pre-existing LLD before THA is of great interest. This article caused me to reflect on how important some well-known intraoperative mitigation strategies are to minimize significant LLD issues during surgery. Several advanced methods have been developed to address LLD, including accelerometer-based portable navigation system, preoperative digital templating (PDT), robot-assisted surgery, the anatomical marker positioning method (shoulder-to-shoulder) and the artificial intelligence-based three-dimensional planning (AIHIP) system[2-5].

The “shoulder-to-shoulder” method is a combined physical and digital technique which includes the following steps: Before surgery (preoperative planning) the femoral “shoulder” must be aligned with the “shoulder” of the digital template. During surgery the “femoral shoulder” must be identified. Then, the femoral stem prosthesis must be implanted after osteotomy with an osteotomy template using the “shoulder-to-shoulder” approach[5]. Unfortunately, the AIHIP system is not widely available as it remains in the third-party development and promotion stage[5]. In 2022, Anjiki et al[2] reported that an accelerometer-based transportable navigation system was valuable for the intraoperative correction of LLD during THA for patients in the supine position.

Wong et al[3] employing PDT improved the likelihood of restoring LLD to within 5 mm and significantly enhanced the probability of preventing excess lengthening > 10 mm. PDT also markedly enhanced the likelihood of accurately re-establishing femoral offset to match the preoperative native hip. Diminished offset was observed mainly in the non-digitally templated patients[3].

In patients undergoing THA due to osteonecrosis of the femoral head, Ma et al[4] encountered significant difference in postoperative LLD between a robot-assisted posterior approach and a manual posterior approach.

The novel artificial anatomical marker positioning method (shoulder-to-shoulder) and the AIHIP system demonstrated good consistency in averting LLD in THA[5]. Surgeons who perform THA procedures regularly should be aware of these developments as a fundamental objective of this surgical intervention is to avoid LLD. However, it is important to emphasize that the aforementioned techniques have some relative strengths and limitations. Robot-assisted THA can diminish the variability of LLD and improve component positioning, although questions endure regarding its cost-effectiveness and steep learning curve. Alternatively, PDT is widely available and economically cost-effective, but its accuracy can decrease in patients with atypical pelvic anatomy or more complex deformities. Portable accelerometer-based navigation systems offer an encouraging compromise, yielding intraoperative guidance without the infrastructure requirements and costs of robotic platforms.

Equally important is the clinical context. Discrepancies, often greater than 5-10 mm, may result in altered gait mechanics, low-back pain, or the perception of limb inequality. These issues can directly affect patient satisfaction and functional recovery, even if radiographic results seem acceptable. Moreover, understanding how LLD impacts long-run prosthesis survival or the risk of revision would establish whether accurate limb-length restoration is not merely a cosmetic concern but a determinant of durable results.

However, it is worth noting that no technique completely eliminates the possibility of post-surgical LLD. Complex deformities, intraoperative instability, and soft-tissue imbalances can still lead to measurable discrepancies, despite the utilization of advanced tools. At the same time, the availability and growing confidence in these technological advances raises challenges related to cost, accessibility, and the training needed for safe implementation - particularly in resource-limited settings.

CONCLUSION

Looking ahead, artificial intelligence systems such as AIHIP offer a timely and exciting direction. These platforms combine three-dimensional planning with intraoperative decision support, potentially diminishing variability across orthopedic surgeons and institutions. Future research should define whether such systems can improve not only radiographic precision but also functional recovery, complication rates, and the long-run survival of implants.

ACKNOWLEDGEMENTS

My sincere thanks to William J. Ribbans, Faculty of Health, Education and Society, University of Northampton, Northampton, United Kingdom, for editing the English of this manuscript.