Comparative Analysis of Sagittal Plane Radiographic Landmarks Used to Identify the Femoral Attachments of Lateral Knee Structures

Purpose: To compare previously described radiographic parameters for the localization of lateral knee (LK) structures, including the popliteus tendon (Pop), anterolateral ligament (ALL), and lateral collateral ligament (LCL) to determine which method best estimates the femoral attachment of each LK structure.

Methods: Twenty-nine human cadaveric knee specimens were carefully dissected to identify the LCL, ALL and Pop. The femoral attachment for each structure was labeled with a radiopaque bead. LK radiographic images were obtained using fluoroscopy. Two radiographic approaches were used to identify each LK structure (Pop-A, Pop-B, LCL-A, LCL-B, ALL-A, and ALL-B) using previously published methods based on radiographic landmarks including the posterior femoral cortex and Blumensaat’s line. The identification of radiographic landmarks was repeated at two different time points by two different surgeons to determine a Pearson’s correlation between values as well as inter- and intra-observer reliability and reproducibility. A paired t-test was conducted to compare the distance from the actual attachment site (as determined by the bead location) and the two radiographically identified estimations of attachment locations.

Results: For the LCL, the mean difference between the actual location and the estimated location via application of LCL-B method (5.0mm ± 2.4) was significantly less than that estimated using LCL-A (8.2mm ± 3.3), p<.0001. Likewise, methods Pop-B (5.7mm ± 2.0) and ALL-B (9.3mm ± 4.5) were shown to have a smaller difference between the actual and estimated femoral attachment site of the popliteus tendon insertion and the ALL insertion, respectively, p<0.0001. Methods for estimating the ALL femoral origin were the worst of the LK structures analyzed, with 90% of estimated values > 5 mm from its anatomic origin. Inter- and intra-observer interclass correlation coefficients were 0.785 or higher.

Conclusion: Previously described radiographic methods for localization of the femoral attachment sites of lateral knee structures resulted in estimated locations that were significantly different than the locations of the radiographic beads placed at the anatomic femoral attachment site of these structures. Therefore, radiographic methods used to localize the femoral attachments of the lateral knee structures may not be reliable.

Clinical relevance: This study demonstrates the variability of anatomy of lateral knee structures and the lack of reproducible radiographic criteria to identify these structures. As a result, there will be decreased reliance on radiographic landmarks to identify the placement femoral grafts and fixation when reconstructing these structures.