The knee straps you are referring to are a form of patellar orthotics (bracing) called infrapatellar straps or bands. They are designed to reduce knee pain, especially in athletes who experience knee pain with running and/or jumping. But they can be used by anyone with pain associated with patellar tendinopathy.
Tendinopathy refers to any tendon that has been damaged in some way but is no longer in the acute inflammatory phase (which would be called a tendinitis). Examination of tendon tissue in patients who have had chronic pain over months and sometimes even years showed scarring and fibrosis but no active fluid, swelling, or white blood cells at the site needed for healing.
There aren’t very many high-quality studies published showing the results of using this strap for knee pain. One recent publication from Michigan State University was based on healthy men who did not have knee pain. Two different brands of these infrapatellar straps were used and compared.
They found that for most (but not all) of the men, there was a significant decrease in strain on the patellar tendon using either type of strap. No known reason could be found for the few men who showed no change with the strap.
As we mentioned, the study was done on normal, healthy men without knee problems. The results may or may not be the same as if applied to patients with knee pain associated with jumper’s knee. The use of these straps to prevent patellar-tendon problems must be investigated. Likewise, the effectiveness of the straps for other kinds of knee problems should be studied.
Before using the strap, you may want to see an orthopedic surgeon and get a proper diagnosis for your knee pain. Knowing the exact cause and mechanism of knee pain is usually prescriptive — in other words, this information directs treatment based on what we know is most successful for each individual diagnosis.