The effect of scapular position on subacromial contact behavior: a cadaver study

Area of Science:

• Biomechanics
• Orthopedics
• Shoulder Anatomy

Background:

• Subacromial impingement is associated with abnormal scapular positioning during shoulder elevation.
• The precise relationship between scapular position and subacromial impingement remains unclear.

Purpose of the Study:

• To biomechanically investigate the effect of scapular position on subacromial contact pressure.
• To clarify the role of scapular positioning in subacromial impingement.

Main Methods:

• Utilized 9 fresh frozen cadaver shoulders to measure peak contact pressure on the coracoacromial arch using a tactile force sensor.
• Simulated various scapular positions, including downward rotation, internal rotation, and anterior tilt, during passive glenohumeral elevation.

Main Results:

• Peak contact pressure significantly decreased with increasing anterior tilt of the scapula.
• Anterior tilt by 20° resulted in a significant reduction in peak contact pressure compared to the neutral position.
• Other scapular rotations (downward, internal) and combined abnormal positions did not significantly alter peak contact pressure.

Conclusions:

• Scapular anterior tilt effectively reduces subacromial contact pressure during shoulder elevation.
• Scapular downward and internal rotations have minimal impact on contact pressure.
• Observed abnormal scapular motions in patients may not be the primary cause of subacromial impingement symptoms.