Tensile characteristics of the acromioclavicular joint: a systematic review and meta-analysis.

BACKGROUND: Understanding the biomechanical roles of the acromioclavicular and coracoclavicular ligaments is essential for optimizing surgical treatment of acromioclavicular joint injuries. This systematic review and meta-analysis investigates the tensile characteristics of the acromioclavicular joint to identify the ligamentous structures contributing to stability. METHODS: A comprehensive search of the Cochrane, Scopus, and PubMed databases was conducted through January 2025 to identify cadaveric studies reporting tensile characteristics of the intact acromioclavicular joint ligaments; studies of repaired or reconstructed joints were excluded. Twenty-six studies involving 374 shoulders met the inclusion criteria. Data on failure load, deformation, energy absorption, and stiffness were extracted, pooled, and compared between ligament groups with Welch t-tests (significance P < 0.05). FINDINGS: The combined acromioclavicular and coracoclavicular complex and the isolated coracoclavicular ligaments demonstrated significantly higher ultimate failure loads than the isolated acromioclavicular, conoid, or trapezoid ligaments (P < 0.05). Failure load did not differ significantly between the combined complex and the isolated coracoclavicular ligaments, but the combined complex and the isolated acromioclavicular ligament exhibited significantly greater deformation and energy absorption at failure than the isolated coracoclavicular group (P < 0.05). Midsubstance tears were the most common failure mode. INTERPRETATION: This review reinforces the coracoclavicular ligaments as the primary stabilizers against superior displacement in high-energy conditions. However, the acromioclavicular ligament contributes significantly to energy absorption and deformation capacity, suggesting that surgical techniques should address all ligamentous structures to effectively restore native stability. CLINICAL TRIAL REGISTRATION: Not applicable (review article).