**Core Concept**
Painful arc syndrome is a clinical condition characterized by pain experienced during abduction of the arm between 60° to 120°, caused by mechanical impingement of soft tissues beneath the acromion. This condition is often associated with rotator cuff pathology and subacromial impingement.

**Why the Correct Answer is Right**
A complete tear of the supraspinatus tendon would likely lead to instability and malalignment of the shoulder joint, rather than mechanical impingement, which is the primary cause of painful arc syndrome. In cases of complete tears, the tendon is often retracted, and the subacromial space may be widened, reducing the likelihood of impingement. The supraspinatus tendon plays a crucial role in stabilizing the humeral head within the glenoid cavity, and its complete tear would alter the normal biomechanics of the shoulder joint.

**Why Each Wrong Option is Incorrect**
**Option B:** A fracture of the greater tuberosity would disrupt the normal anatomy of the proximal humerus, potentially leading to painful arc syndrome due to mechanical impingement of surrounding soft tissues.

**Option C:** Subacromial bursitis involves inflammation of the bursa between the acromion and the rotator cuff tendons, leading to pain and mechanical impingement, which are hallmarks of painful arc syndrome.

**Option D:** Supraspinatus tendinitis involves inflammation of the tendon, which can lead to mechanical impingement and painful arc syndrome.

**Clinical Pearl / High-Yield Fact**
Painful arc syndrome is often associated with rotator cuff tendinitis and subacromial impingement, which can be managed conservatively with physical therapy, corticosteroid injections, and activity modification.

**✓ Correct Answer: A. Complete tear of supraspinatus**