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Human Evolution and Subacromial Impingement

Explore how anatomical risk factors in human scapulae may contribute to subacromial impingement and rotator cuff tears. Findings suggest these factors are not unique to humans, challenging existing theories. Discover the implications for shoulder health.

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Human Evolution and Subacromial Impingement

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  1. Human Evolution andSubacromial Impingement JD Craik, R Malina, V Ramasamay & NJ Little

  2. Subacromial Impingement & Rotator Cuff Tears • 44% to 65% of all shoulder complaints • Two main theories: • Mechanical (extrinsic) theory • Degenerative (intrinsic) theory

  3. Anatomical Risk Factors Bigliani Classification Type I Type II Type III

  4. Anatomical Risk Factors Coracoacromial Arch Height AH

  5. Anatomical Risk Factors Acromion Ventral Projection AVP

  6. Anatomical Risk Factors Acromion Tilt AT

  7. Anatomical Risk Factors Acromioglenoid Angle AGA

  8. Anatomical Risk Factors Coracoglenoid Angle CGA

  9. Anatomical Risk Factors Acromion Lateral Projection ALP

  10. Anatomical Risk Factors Coracoid Lateral Projection CLP

  11. Anatomical Risk Factors Glenoid Version GV

  12. Anatomical Risk Factors Glenoid Inclination GI

  13. 6 Mya 7 Mya 14 Mya

  14. Hypothesis • Anatomical risk factors unique or accentuated in human scapulae may play a more direct role in subacromial impingement and rotator cuff tear aetiology.

  15. Methods

  16. Methods • Dry Bone Scapulae • 22 human • 17 gorilla • 13 chimpanzee • 12 orangutan

  17. Methods

  18. Fiji Image J Software • Microsoft Excel (Mac 2008)

  19. Methods Vertebral Border Length VBL

  20. Methods Supraspinatus Area Infraspinatus Area

  21. Results Bigliani Classification Type I Type II Type III

  22. Results Coracoacromial Arch Height Increased Risk mm

  23. Results Acromion Ventral Projection Increased Risk mm

  24. Results Acromion Tilt Increased Risk Degrees

  25. Results Acromioglenoid Angle Increased Risk Degrees

  26. Results Coracoglenoid Angle Increased Risk Degrees

  27. Results Acromion Lateral Projection Increased Risk mm

  28. Results Coracoid Lateral Projection Increased Risk mm

  29. Results Glenoid Version Increased Risk Degrees

  30. Results Glenoid Inclination Increased Risk Degrees

  31. Therefore: • These anatomical risk factors are not unique to humans! • The extrinsic theory is not supported by these results as a primary aetiological factor

  32. Results Fossa Ratio ???

  33. Conclusions • This study aimed to determine if any of the risk factors associated with impingement and rotator cuff tears are accentuated in humans • The extrinsic theory is not supported by these results as a primary aetiological factor • Reduction in Supraspinatus Fossa Size • Muscle / tendon insufficiency ? • Force vector shift ?

  34. Thank You

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