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I went with a friend to the doctor's for a shoulder problem. The doctor was holding a handheld device against her wrist to test for a rotator cuff tear. How does that work?

You may have seen a dynamometer used to measure maximal forces in the shoulder. It's a measure of the force of a contracting muscle. A pressure plate is held against the patient's wrist while he or she presses against it as hard as possible. This type of muscle contraction is called isometric.

The gauge reads peak force in newtons. Some dynamometers also measure the time it takes to reach peak force and the total test time. As a manual muscle tester, it's accurate, objective, and reliable.

Researchers in Australia have tested patients with rotator cuff tears using a dynamometer and compared the results with healthy adults without a rotator cuff tear. They found that the dynamometer is a useful tool when screening for rotator cuff tears. It is noninvasive, inexpensive, and easy to use.

Now muscle strength can be measured before and after surgery and before, during, and after rehab. It's not 100 percent accurate so only during surgery is the diagnosis confirmed but dynamometer testing for rotator cuff tears could replace expensive imaging such as MRIs.

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