This cadaveric study used strain gauges to measure tension in all the major static restraints of the shoulder across different positions. It asked how the glenohumeral ligaments, posterior capsule, and coracohumeral ligament share the job of stabilizing the joint. Earlier work had focused mainly on the anterior glenohumeral ligaments.
The core mental model: shoulder stability is a distributed job, not a single-ligament job. At any position, the restraints share load, and the one under greatest tension is the one that fails. Combine the position of the arm with the direction of force, and you can predict which structure is injured.
Apply it directly. Abduction, extension, and external rotation loads the anterior inferior glenohumeral ligament to 84%, which is the anterior-inferior dislocation and Bankart lesion. Flexion, adduction, and internal rotation loads the posterior capsule, which is posterior dislocation.
The study also explains frozen shoulder as a state where all restraints tense at once, eliminating coupled motion and "freezing" the joint. Remember the limits: this is a cadaveric model with no muscle or inertial forces, and calibration introduced roughly a 10% bias. The value is the framework, not the exact percentages.
This cadaveric study used strain gauges to measure tension in all the major static restraints of the shoulder across different positions. It asked how the glenohumeral ligaments, posterior capsule, and coracohumeral ligament share the job of stabilizing the joint. Earlier work had focused mainly on the anterior glenohumeral ligaments.
The core mental model: shoulder stability is a distributed job, not a single-ligament job. At any position, the restraints share load, and the one under greatest tension is the one that fails. Combine the position of the arm with the direction of force, and you can predict which structure is injured.
Apply it directly. Abduction, extension, and external rotation loads the anterior inferior glenohumeral ligament to 84%, which is the anterior-inferior dislocation and Bankart lesion. Flexion, adduction, and internal rotation loads the posterior capsule, which is posterior dislocation.
The study also explains frozen shoulder as a state where all restraints tense at once, eliminating coupled motion and "freezing" the joint. Remember the limits: this is a cadaveric model with no muscle or inertial forces, and calibration introduced roughly a 10% bias. The value is the framework, not the exact percentages.