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BIOMECHANICS OF THE FROZEN SHOULDER

What is biomechanics?

Biomechanics is an interdisciplinary science that studies the application of mechanical principles to a living organism using knowledge of anatomy, physiology, physics, and pathophysiology. Kinematics studies the movement of bones and joints, and kinetics studies the forces that cause or stop the movement.

The human body is affected by numerous internal and external forces. Internal forces are a product of the structure of the body itself and can be active (muscle force) and passive (tension of connective tissue). External forces are the product of the interaction of the body and forces outside the body, such as gravitational force and the reaction force of the substrate.

Good biomechanics of movement is one of the important tools, and understanding it gives us a better insight into the process of pain emergence and rehabilitation.

Kinesiologist Marko Drašković and football player
Shoulder joint

Biomechanics of the shoulder joint

The shoulder joint is a very mobile joint with less stability at the same time. Injury to just one joint, tendon or muscle can impair overall shoulder function. Muscles do not work in isolation but in synergy. It is the synergy of joints with muscles that ensures a wide range of movement and stability.

4 joints are responsible for shoulder movements:

  1. sternoclavicular (SC) joint
  2. acromioclavicular (AC) joint
  3. glenohumeral (GH) joint
  4. scapulothoracic joint
 
We will give an example of shoulder abduction performed primarily by the deltoid muscle with stabilizing the rotator cuff muscles that require coactivation of 2 muscles, serratus anterior and trapezius to stabilize the scapula and collarbone. Good positioning of the chest and pelvis conditions any movement of the extremities, including in the shoulder joint.
 
A number of studies have shown that people with subacromial impingement syndrome can generally be expected to decrease the following movements:
  • downward rotation of the scapula
  • upward rotation of the scapula
  • external rotation of the scapula

Biomechanics of the frozen shoulder

The glenohumeral (GH) joint is located distally and is the most mobile part of the shoulder. At the same time, it is more susceptible to instability, especially due to a large number of repetitive movements with inadequate muscle control.

It is the GH joint that is often affected by pathologies of a degenerative nature, for example, adhesive capsulitis, known as "frozen shoulder". The characteristics are stiffness, reduced passive and active mobility, and pain in the shoulder.

If the cause is trauma (secondary form) then in particular we need to ensure the variability of movement. When we align this with the movements of the chest and good positioning of the body then we are talking about good biomechanics of movement.

Load progression is also an important component of rehabilitation and it is often very neglected.

In order to reduce the risk of Frozen Shoulder syndrome, it is necessary to ensure good biomechanics of the shoulder, good chest movements, and good positioning of the body. 

See what is exactly Frozen Shoulder Syndrome , how it is diagnosed and treated. 

Biomechanics of the shoulder
Picture of Mag. Cin. Marko Drašković

Mag.Cin. Marko Drasković

Marko is a kinesiologist, kinesiotherapist and lecturer in biomechanics education, working on rehabilitation and recovery of top athletes within his clinic in Velika Gorica.

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