Posterosuperior displacement due to rotator cuff tears

Area of Science:

• Orthopedic biomechanics
• Shoulder joint mechanics
• Rotator cuff pathology

Background:

• Rotator cuff tears (RCTs) can lead to glenohumeral instability.
• Understanding the biomechanical role of different rotator cuff muscles and the long head of the biceps tendon (LHB) is crucial for managing RCTs.

Purpose of the Study:

• To compare the biomechanical effects of varying sizes of anterosuperior and posterosuperior rotator cuff tears (RCTs).
• To evaluate the influence of long head of the biceps tendon (LHB) loading on posterosuperior glenohumeral translation in the presence of RCTs.

Main Methods:

• Ten cadaveric shoulder specimens were used.
• Posterosuperior glenohumeral translation was measured under load with intact rotator cuffs and sequentially larger anterosuperior and posterosuperior RCTs.
• Measurements were taken with and without LHB loading.

Main Results:

• Cutting the infraspinatus resulted in significantly greater posterosuperior translation than cutting the subscapularis.
• LHB loading consistently reduced posterosuperior translation across all RCT sizes, with a greater percentage decrease observed in larger tears.
• LHB loading was more effective in reducing anterosuperior translation for anterosuperior RCTs compared to superior/posterosuperior translation.

Conclusions:

• The infraspinatus plays a critical role as a dynamic stabilizer against posterosuperior glenohumeral translation.
• LHB loading offers a stabilizing effect on glenohumeral translation in the context of RCTs.
• Understanding these biomechanical principles can inform treatment strategies for rotator cuff injuries.