Mechanical Properties of the Shoulder Ligaments under Dynamic Loading

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Human Anatomy

Background:

• Understanding the mechanical properties of shoulder joints is crucial for diagnosing injuries and developing effective treatments.
• Previous research has primarily focused on quasi-static loading, with limited data on high-speed impact responses.

Purpose of the Study:

• To evaluate the biomechanical properties and failure modes of human shoulder joints (acromioclavicular, coracoclavicular, sternoclavicular) under quasi-static and high-speed loading conditions.
• To compare failure patterns and mechanical characteristics across different loading rates.

Main Methods:

• Bone-ligament-bone specimens from 33 human cadaver shoulders were tested.
• Mechanical testing was performed using a high-speed Instron machine at one quasi-static rate (0.1%/sec) and two high rates (15,000%/sec and 40,000%/sec).
• Failure modes, load at failure, stress at failure, strain at failure, and Young's modulus were recorded.

Main Results:

• Ligament failure was common in acromioclavicular and coracoclavicular joints, while sternoclavicular joints predominantly failed at the bone.
• Bone fractures occurred more frequently at the clavicle (acromioclavicular) and coracoid (coracoclavicular).
• Quasi-static and high rate 2 (15,000%/sec) tests showed more bone fractures than high rate 1 (40,000%/sec).
• Young's modulus, ultimate stress, and ultimate load were significantly lower in quasi-static tests compared to high rate 2 tests.
• No significant correlation was found between specimen dimensions (cross-sectional area) or demographic data (age, height, weight) and mechanical properties.

Conclusions:

• Shoulder joint failure modes and mechanical responses are rate-dependent.
• High-speed impacts may lead to different injury patterns compared to slower loading.
• Age, height, and weight do not appear to be significant predictors of shoulder joint mechanical properties in this cohort.