Joints are so interesting in how they can move and how
different joints work together to create certain actions, and with injury to
one of those joints how it affects that motion altogether. Take the shoulder,
for example. A simple ball and socket joint called the glenohumeral joint, but
in order for you to reach over head for something or for an activity like
volleyball you also have to have a joint in conjunction with this one in order
to reach full range of motion. This joint is called the scapulothoracic joint.
When these joints are paired together, this is called scapulohumeral rhythm. They
work in a 2:1 ratio, where the glenohumeral (GH) joint works in 2 degrees of
motion, while the scapulothoracic (SC) joint works in 1 degree of motion. When
these joints are working together synchronously, it protects the contents
within the subacromial space. However, if the scapula is injured or not
rotating upward properly, this can cause impingement to the subacromial space
resulting in pain. Also, the humeral head must rotate laterally in order to
complete full ROM, along with rolling and gliding in the glenoid fossa which is
a decrease in shear forces. So, it is imperative that these joints stay in
conjunction with each other in order to have full functioning capacity, so… stay
healthy, stay strong, and stay educated!
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