and the elbow bent to 90 degrees the person tries to rotate outwards against resistance). A combination of tests seems to provide the most accurate diagnosis. For impingement, these tests include the Hawkins-Kennedy impingement sign in which an examiner medially rotates the injured individual's flexed arm, forcing the supraspinatus tendon against the coracoacromial ligament and so producing pain if the test is positive a positive painful arc sign, and weakness in external rotation with the arm at the side. For the diagnosis of full-thickness rotator cuff tear, the best combination appears to include once more the painful arc and weakness in external rotation, and in addition, the drop arm sign. This test is also known as Codman's test. The arm is raised to the side to 90° by the examiner. The injured individual then attempts to look to lower the arm back to neutral, palm down. If the arm drops suddenly or pain is experienced, the test is considered positive. MRI Magnetic resonance imaging (MRI) and ultrasound are comparable in efficacy and helpful in diagnosis although both have a false positive rate of 15–20%. MRI can reliably detect most full-thickness tears although very small pinpoint tears may be missed. In such situations, an MRI combined with an injection of contrast material, an MR-arthrogram, may help to confirm the diagnosis. It should be realized that a normal MRI cannot fully rule out a small tear (a false negative) while partial-thickness tears are not as reliably detected. While MRI is sensitive in identifying tendon degeneration (tendinopathy), it may not reliably distinguish between a degenerative tendon and a partially torn tendon. Again, magnetic resonance arthrography can improve the differentiation. An overall sensitivity of 91% (9% false negative rate) has been reported indicating that magnetic resonance arthrography is reliable in the detection of partial-thickness rotator cuff tears. However, its routine use is not advised, since it involves entering the joint with a needle with potential risk of infection. Consequently, the test is reserved for cases in which the diagnosis remains unclear. Ultrasound Musculoskeletal ultrasound has been advocated by experienced practitioners, avoiding the radiation of X-ray and the expense of MRI while demonstrating comparable accuracy to MRI for identifying and measuring the size of full-thickness and partial-thickness rotator cuff tears. This modality can also reveal the presence of other conditions that may mimic rotator cuff tear at clinical examination, including tendinosis, calcific tendinitis, subacromial subdeltoid