Biology
Kinematics of the Scapulothoracic Joint in Shoulder Pathology
Quick fact
In many shoulder problems, like impingement or rotator cuff tears, the scapula doesn't move normally—often showing less upward rotation and posterior tilt, which can narrow the space for tendons and lead to pain.
Why this is interesting
When you raise your arm overhead, your shoulder blade is doing a hidden dance. But what happens when that dance goes wrong?
Read the full explanation
Understanding Kinematics of the Scapulothoracic Joint in Shoulder Pathology
The scapulothoracic joint isn't a typical joint with bones meeting; it's a 'functional' joint where the scapula (shoulder blade) glides over the ribcage. It moves in several ways: elevation/depression, protraction/retraction, upward/downward rotation, and anterior/posterior tilt. When you lift your arm, your scapula must rotate upward to keep the arm in a good position. Think of the scapula as a platform: if it's tilted the wrong way, the arm's ball (humeral head) can hit against the roof (acromion), causing pain. In shoulder pathologies, this coordinated motion breaks down, a condition called scapular dyskinesis.
A deeper explanation
The scapulothoracic joint works via muscles like the serratus anterior, trapezius, and rhomboids. In a healthy shoulder, the scapula upwardly rotates about 60 degrees during full arm elevation, contributing to a smooth 'scapulohumeral rhythm.' In pathologies, muscle imbalances or pain alter this rhythm. For example, reduced upward rotation or posterior tilt can decrease the subacromial space, impinging the supraspinatus tendon. Rotator cuff tears can further disrupt force couples, leading to compensatory movements. Understanding these kinematics helps clinicians identify why pain occurs and design exercises to correct muscle activation patterns, improving function and reducing symptoms.