What Is the Anatomic Footprint of the Anterolateral Ligament of the Knee? A Race- and Sex-based MRI Analysis.

BACKGROUND The anatomic location of the anterolateral ligament (ALL) of the knee is critical to ALL reconstruction, but there is not a clear consensus about the location of its footprint. Knowledge of the anatomic footprint is necessary to assess intraoperative positioning and postoperative functional outcomes of ALL reconstruction. Furthermore, while racial and sex-related variations in the ACL have been well documented, it remains unknown whether such differences extend to the ALL, as well as whether these differences influence surgical strategies. QUESTIONS/PURPOSES We generated three-dimensional (3D) models based on MRI scans to (1) describe the differences in the ALL position between Chinese and White patient groups by establishing its anatomic footprint relative to adjacent anatomic structures, (2) assess the length of the ALL and the correlation between the ALL sagittal plane orientation and the position of its footprints, and (3) simulate the risk of injury to the lateral collateral ligament (LCL) while reconstructing the ALL by the use of drills of various diameters. METHODS In our institution, patients' information was systematically gathered through a prospective database framework. Participants independently provided demographic details via a structured survey questionnaire, which were then recorded by our team of well-trained researchers. The collected data encompassed age, sex (female and male), ethnic background (White and Chinese), height (centimeters), weight (kilograms), and BMI (kg/m2). This study involved 120 volunteers, including 60 Chinese and 60 age-, sex-, and BMI-matched White participants, whose normal knees were scanned with MRI to generate 3D models. ALL femoral and tibial footprints were identified and digitally delineated on MRI images by two board-certified orthopaedic surgeons. Subsequently, the locations of the ALL femoral and tibial footprints were identified in relation to adjacent anatomic structures. The length of the ALL from the femoral footprint to tibial footprint was then measured, together with the angle formed by the ALL in the sagittal plane relative to a line parallel to the anatomic axis of the femur. Through regression analysis, we explored the correlation between the sagittal orientation of the ALL and the position of the footprint. Finally, simulations of ALL femoral tunnel drilling were performed to assess damage to the LCL footprint center caused by the use of drills of varying diameter. RESULTS The ALL femoral footprint was adjacent to both the lateral epicondyle and the LCL, positioned anterior and distal to the LCL attachment, while the ALL tibial footprint was located between the Gerdy tubercle and the fibular head. The mean ± SD femoral footprint of the ALL in the Chinese population was more distal and anterior compared with the White population, which was located posterior to the lateral epicondyle (4 ± 2 mm versus 5 ± 2 mm, mean difference 1 [95% confidence interval (CI) 0 to 2]; normalized p value = 0.03) and distal to the lateral epicondyle (8 ± 3 mm versus 6 ± 2 mm, mean difference 2 [95% CI 1 to 2]; normalized p value = 0.005). There were differences between Chinese patients and White patients at ALL tibial footprint locations, where the distance from the fibular head was 21 ± 3 mm versus 22 ± 4 mm (mean difference 1 [95% CI 0 to 2]; normalized p value = 0.02), and the distance from the lateral tibial plateau was 7 ± 1 mm versus 8 ± 2 mm (mean difference 1 [95% CI 0 to 1]; normalized p value = 0.004). The ALL length was longer in White patients than in Chinese patients (33 ± 4 mm versus 29 ± 3 mm, mean difference 4 [95% CI 3 to 5]; normalized p < 0.001). Multiple linear relationships were observed between the ALL sagittal plane angle and the normalized locations of the ALL femoral and tibial footprints (R = 0.32, mostly correlated). In the posterior directions relative to the lateral epicondyle, the femoral footprint location exhibited an effect on the sagittal angle (p = 0.001). With every 4 mm of posterior movement of the ALL femoral footprint relative to the lateral epicondyle, the sagittal plane angle decreases by about 3.2°. Based on the distance between the ALL and LCL, when simulating femoral tunnel drilling using drill diameters > 8 mm in the Chinese group and > 7 mm in the White group, the LCL footprint center would be substantially damaged in more than one-half of the patients. CONCLUSION Minor differences were observed in the ALL footprints between Chinese and White populations, although no sex-related variations were found. These race-specific discrepancies highlight the need for personalized surgical approaches. In tunnel positioning, the ALL femoral footprint in Chinese populations was located more distal and anterior relative to the lateral epicondyle compared with the White populations. Regarding graft length, White individuals exhibited longer ALL dimensions than Chinese individuals, necessitating prioritization of longer grafts. For graft diameter, in the White group, the ALL footprint distance to the LCL footprint was closer compared with the Chinese group, indicating higher risks of LCL injury during ALL reconstruction. Notably, a linear association existed between the ALL sagittal angle and femoral footprint, offering quantitative guidance for intraoperative precision. CLINICAL RELEVANCE For patients with ALL injuries of the knee or revision surgeries where the native footprint cannot be identified, 3D MRI reconstruction technology enables precise 3D reconstruction of the ALL footprint using anatomic landmarks from the healthy side. This provides surgeons with effective preoperative planning guidance, intraoperative navigation support, and postoperative clinical function assessment. The established relationship between ligament sagittal angles and footprint positioning assists in real-time intraoperative evaluation of tunnel placement and postoperative accuracy verification. Additionally, our data revealed that the distance between the ALL footprint and LCL footprint was shorter in the White group compared with the Chinese group. Based on this anatomic variation, it is recommended to set the upper limit of ALL femoral tunnel diameter at 8 mm for the Chinese group and 7 mm for the White group. Further biomechanical studies are required to precisely define the safety threshold for graft diameter, ensuring graft stability while minimizing the risk of iatrogenic LCL injury.