A 58-year-old male mason presents with a 3-month history of progressive right shoulder pain and weakness. He reports difficulty lifting objects overhead and pain radiating down the lateral arm. On examination, he has positive Neer's impingement sign, Hawkins-Kennedy test, and a positive 'drop arm' sign. Passive range of motion is preserved. MRI shows a full-thickness tear of the supraspinatus tendon with mild retraction. What is the primary anatomical consequence of this injury?