The Anatomy and Length Changes of the Lateral Patellofemoral Ligament and Lateral Patellotibial Ligament

Abstract

Objectives:The lateral patellar restraints (lateral patellofemoral ligament [LPFL], lateral patellotibial ligament [LPTL] and lateral patellomeniscal ligament [LPML]) are relatively poorly understood entities, which are important in patellar stability. The purpose of this study is to perform a qualitative and quantitative anatomic evaluation of the LPFL, LPML, and LPTL attachment sites, with specific attention to their relationship to pertinent osseous and soft tissue landmarks.Methods:Six non-paired, fresh frozen human cadaveric knees (n = 6) were utilized for this study. Institutional review board approval was not required for this cadaveric study. Knees were dissected and a variety of anatomic locations and the LPFL, LPTL, and LPML attachment sites and attachment centers were marked with surgical marker. The knee was placed in a custom jig and the quadriceps tendon was loaded with a 1 kg weight. Ligament area was measured with a portable coordinate measuring device (Microscribe, Solution Technologies, Oella, MD) and ligament centers were identified at 0, 15, 30, 45, 60 and 90° of flexion. The 3D location via a ‘bird’s eye view’ was calculated in Rhinoceros 5.0 software (McNeel North America, Seattle, WA). Data analysis was performed in MATLAB (MathWorks, Natick, MA) and Microsoft Excel (Microsoft, Redmond, WA). Statistical analysis was conducted with one-way repeated measure ANOVAs and Spearman Rank Correlation, which was used for non-normally distributed data, in SPSS (v26, IBM, Armonk, NY).Results:The location of the LPFL on the femur was compared to local landmarks (Fig 1). In the sagittal plane, the center, anterior, and posterior aspect of the LPFL were a mean of 17.0±1.4, 11.8±2.0, and 8.0±1.9 mm from the lateral epicondyle, respectively. Distances to the anterior, central, and posterior cartilage from these locations were 14.3±1.8, 14.6±2.9, and 14.3±3.3mm, respectively. The area of the LPFL was a mean of 31.59±20.24mm2 in the vertical plane. The location of the LPFL on the patella was then analyzed. The superior aspect of the LPFL was 8.52±2.74 mm from the superior pole of the patella, while the distance from the inferior pole to the LPFL was 14.01±4.53mm. The average length of the patella was 4.10±0.34cm and the LPFL occupied 45.09% of its sagittal length. The distance from the LPML to the anterolateral root was 7.35±2.98mm. The center of the LPTL on the tibia was a mean distance of 5.88±3.00mm from Gerdy’s tubercle. LPFL length decreased in flexion with a mean length of 40.60±3.24mm at 0°, 36.27±6.29mm at 15°, 33.77±4.93mm at 30°, 31.41±4.72 mm at 45°, 30.05±4.10mm at 60°, and 26.05±3.02mm at 90°. Significant length changes through flexion were observed (p < 0.0005), pairwise comparison found significant differences between 0° and 45° (p=0.025), 0° and 60° (p=0.012), and 0° and 90° (p=0.005). However, a significant negative correlation between degree of flexion and length was observed (r=-0.734, p < 0.0005).Conclusions:To our knowledge, this is the first study to describe the anatomy of the components of the lateral stabilizers including the LPFL, LPTL, and LPML. Reproducible locations on the femur and patella were observed for the two LPFL attachments. In addition, the attachment sites were found to have consistent distances to anatomic landmarks. Our results demonstrate that the LPFL length significantly correlates with flexion and maintains isometry through flexion, in contrast to the medial patellofemoral ligament, which has the greatest length changes in the first 20° of flexion.