If you've watched any amount of sports, you may have wondered what those black or white straps around the athletes' knees are for. Those 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.
Do they work? And if so, how do they work? In other words, what's the mechanism behind their success? This is the first study to really take a look at the effect of infrapatellar straps in the treatment of patellar tendinopathy.
The patellar tendon is part of the quadriceps mechanism. The quadriceps muscle is the large, four-part muscle that covers the front of the thigh. Contraction of the quadriceps muscle straightens the knee.
The muscle becomes tendinous around the patella (knee cap) and has its final attachment or insertion point just below the knee cap. The tendon and connective tissue around the tendon act on the patella like a pulley system to pull the tibia (lower leg bone). The final result of a strong contraction is a straight leg.
Repetitive contraction of the patellar tendon/quadriceps muscle can create local mini-trauma at the patellar tendon insertion point below the patella. This type of chronic strain may result in a condition of knee pain referred to as jumper's knee.
As you might have guessed, it's most common among athletes who are engaged in squatting, jumping, and running activities that require moving from knee flexion to knee extension. These are the folks most likely to be seen wearing an infrapatellar tendon strap.
The strap puts pressure on the patellar tendon with the hope of reducing the strain or tension at the point of pain. Despite how the strap looks, it's not designed to actually push the knee cap up.
This study was done to find out what's really going on with these straps. They also used this opportunity to compare one brand of strap to another (e.g., the Cho-Pat Knee Strap and the DonJoy Cross Strap).
Twenty healthy young men with no known knee problems participated in the study. X-rays of the knees were taken with and without each strap and with the knee in a position of flexion (60 degrees of flexion to be exact).
Measurements taken from the X-rays included one angle of the patella called patellar tilt, the angle between the patella and patellar tendon called the patella-patellar tendon angle or PPTA, and the thickness of the patellar tendon in three places. X-rays also showed any changes in the patella's pressure against the femur (thigh bone).
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.
The authors suggested perhaps there were differences in strap tightness or the level of strap placement. An alternate theory proposed was that there may have been some differences in tissue compliance (how much "give" there is in the soft tissue when the strap was applied).
It appears that the decrease in tissue strain is directly linked to the decrease in pain when using these straps. The X-rays confirmed that the patella was not pushed against the femur. The straps do increase the patella-patellar tendon angle (PPTA) and decrease the patellar tendon length.
One additional note about this study. Remember it 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.
Before making any final conclusions, this same type of study must be done on symptomatic athletes. Likewise, the use of these straps to prevent patellar-tendon problems must be investigated. But finding out how the straps work on normal, healthy adults is the place to start!
Reference: Michael Lavagnino, PhD, et al. Infrapatellar Straps Decrease Patellar Tendon Strain as the Site of the Jumper's Knee Lesion: A Computational Analysis Based on Radiographic Measurements. In Sports Health. May/June 2011. Vol. 3. No. 3. Pp. 296-302.