The Anterolateral Ligament of the Knee Is a Nonisometric Thin Ligament With High Prevalence and Almost Constant Attachment to the Lateral Meniscus: A Systematic Review With Meta-analysis

Purpose: To provide comprehensive information about the anterolateral ligament (ALL) prevalence, morphometry, isometry, insertions, histology, and its relationship with the lateral meniscus (LM). Methods: The study was performed, according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Eligible cadaveric studies investigating the frequency of the ALL presence, and anatomical features were identified through an online search of the PubMed, Scopus, and Cochrane Central databases from inception to June 2022. Statistical analysis was conducted with the open-source R programming language using the "meta" package. The Higgins I2 statistic was used for quantifying heterogeneity. Results: Thirty-three studies (1,478 cadaveric knees) were included. The ALL had a 79% prevalence. It was attached to the LM periphery in 97% of studies. Most studies reported a femoral insertion of the ALL, just proximal and posterior to the lateral epicondyle. Tibial attachment is constant at the midpoint between Gerdy's tubercle and fibular head. The mean ALL thickness at the joint line was 1.6 [1.2; 2.0] mm. The ALL length was found to significantly change across the knee flexion (P < .01). It was increased from 0 degrees to 60 degrees and decreased after 60 degrees flexion. Seven histological studies demonstrated a typical ligamentous microstructure. Conclusion: The ALL is a thin ligament, distinct to the knee capsule, which may be found in 79% of the knees having an almost constant attachment to the LM. The ALL is not isometric. It becomes tense during internal rotation and between 30 degrees and 60 degrees knee flexion. Pooled results should be interpreted with caution due to the high heterogeneity among the included studies. Clinical Relevance: This study sheds light on controversial issues and provides comprehensive and accurate information about the essential anatomical knowledge on ALL, which may contribute to optimizing ALL reconstruction surgical techniques and biomechanical settings.