Human evolution and tears of the rotator cuff

Area of Science:

• Comparative anatomy
• Primatology
• Orthopedic research

Background:

• Humans exhibit a higher incidence of rotator cuff tears than other great apes.
• Understanding anatomical differences may elucidate the etiology of these tears.

Purpose of the Study:

• To compare anatomical risk factors for subacromial impingement and rotator cuff tears across great ape species.
• To identify features accentuated in humans contributing to disease aetiology.

Main Methods:

• Digital photographs of scapulae from humans, gorillas, chimpanzees, and orangutans were analyzed.
• Calibrated digital imaging measured anatomical features, scaled by scapula vertebral border length.

Main Results:

• No anatomical features associated with impingement/tears were significantly accentuated in humans compared to other apes.
• The human supraspinatus fossa was found to be significantly smaller than in other species.

Conclusions:

• The smaller human supraspinatus fossa suggests structural insufficiency or altered rotator cuff force vectors as primary factors.
• An alternative primary etiological factor for rotator cuff tears in humans must exist beyond currently studied anatomical features.