**Question:** A 45-year-old man has a fall from his motorcycle and is complaining of shoulder pain. Radiographs are negative for fracture and dislocation. On examination, you noticed positive lift-off test. What is the most likely diagnosis?

A. Rotator cuff tear
B. Glenohumeral dislocation
C. Supraspinatus tendonitis
D. Acromioclavicular joint injury

**Correct Answer:** .

**Core Concept:**
The correct answer is **A. Rotator cuff tear**. The rotator cuff is a group of four muscles and their tendons that stabilize and move the humerus within the glenohumeral joint. Injuries to the rotator cuff can occur due to trauma or repetitive strain, leading to pain and dysfunction in the shoulder.

**Why the Correct Answer is Right:**
In this case, the patient's history of a motorcycle fall and positive lift-off test suggest a traumatic mechanism, making a rotator cuff tear the most likely diagnosis. The positive lift-off test indicates instability at the glenohumeral joint, which can be caused by a rotator cuff tear. Radiographs being negative for fracture and dislocation further supports the diagnosis as trauma-related injuries would likely be detected on X-rays.

**Why Each Wrong Option is Incorrect:**

**A. Rotator cuff tear:** Although the patient has a history of trauma and positive lift-off test, the mechanism is not explicitly motorcycle fall, so it is less likely compared to rotator cuff tear.

**B. Glenohumeral dislocation:** Dislocation can have positive lift-off test, but in this case, the radiographs are negative, making it less likely. Additionally, a dislocation would usually be accompanied by other findings like swelling, deformity, and instability.

**C. Supraspinatus tendonitis:** Tendonitis is inflammation of a tendon, whereas the case presents a tear. Also, tendonitis is usually caused by repetitive strain, while the patient has a recent history of trauma.

**D. Acromioclavicular joint injury:** The radiographs being negative and lift-off test positive narrow down the diagnosis to rotator cuff tear or instability of the glenohumeral joint. The acromioclavicular joint injury would typically present with different clinical findings and may show abnormalities on radiographs.

**Clinical Pearl:** The lift-off test is a positive clinical finding for glenohumeral joint instability. In the context of this case, it is a positive finding for a rotator cuff tear or instability. It is essential to consider this test in the differential diagnosis of shoulder pain and instability, especially after a trauma like the patient's motorcycle fall.