A knee strap, specifically an infrapatellar tendon strap, is a simple band worn just below the kneecap. This device is a conservative treatment option for managing pain in the patellar tendon, which connects the kneecap to the shinbone. The strap is designed to apply targeted pressure to the tendon, which helps to redistribute forces during movement. This article explains the mechanics behind this support and provides guidance on its application.
The Primary Function of Patellar Straps
The patellar strap is a focused compression device that works by applying a counterforce directly onto the patellar tendon. The goal of this localized pressure is to relieve the strain that accumulates at the point of pain, typically where the tendon attaches to the kneecap. By gently compressing the tendon, the strap changes the mechanics of the entire knee-extensor system during activity. This strap is distinct from a full knee sleeve or stabilizing brace, as it focuses action on a very small, specific area of the knee complex.
This device functions as a temporary mechanical aid, allowing individuals to continue activity with reduced discomfort. It is not a cure for the underlying condition but a tool for pain management during dynamic movements like running or jumping. The strap’s effectiveness comes from its ability to alter the forces applied to the tendon. The front center of the strap, usually featuring a pad or cushion, must be positioned correctly over the patellar tendon to achieve the intended counterforce.
How They Reduce Tendon Stress
The pain-relieving effect of the patellar strap is attributed to a change in the biomechanics of the knee joint’s extensor mechanism. When the strap applies pressure to the tendon, it effectively narrows the tendon and alters the angle of pull on the kneecap. Scientific analysis suggests the strap reduces strain by increasing the patella-patellar tendon angle (PPTA) and decreasing the patellar tendon length. This modification helps to reduce the maximum localized strain within the part of the tendon commonly affected by injury.
The strap functions by shifting the point of maximum stress away from the most tender, inflamed area of the tendon, typically near the attachment to the kneecap. This change in force distribution supports the counterforce mechanism. One study found that infrapatellar straps significantly decreased the predicted localized patellar tendon strain during simulated jump landings. Specifically, the localized strain was reduced by an average of over 30% in many cases.
The strap does not push the kneecap upward, as some might assume. Instead, it serves to maintain proper alignment and reduce the magnitude of force on the tendon. The degree of tightness and the precise location are significant factors influencing how much the strap can reduce the strain.
Conditions Relieved by Straps
The infrapatellar strap is most commonly used for conditions involving the patellar tendon itself, primarily Patellar Tendinopathy, often called Jumper’s Knee. This condition is characterized by pain and tenderness directly on the patellar tendon, resulting from repetitive, forceful quadriceps contractions common in sports involving jumping and running. The targeted compression helps manage the pain associated with the excessive loading of the tendon.
Another condition where these straps are frequently effective is Osgood-Schlatter disease, which affects adolescents. This involves inflammation at the growth plate where the patellar tendon attaches to the shinbone. The strap reduces the tension on this attachment point, providing relief during physical activity. The device is also sometimes used for mild cases of Patellofemoral Pain Syndrome, or Runner’s Knee, to help with pressure distribution around the kneecap.
While the strap may help improve the alignment of the kneecap’s movement in cases of Patellofemoral Pain Syndrome, it is considered most effective for true tendon issues. These include Jumper’s Knee and Osgood-Schlatter disease.
Proper Placement and Usage
Correct placement is necessary for the patellar strap to provide its intended mechanical benefit. The strap should be positioned directly over the patellar tendon, which is the thick band of tissue just below the kneecap. The center of the strap, often a padded section, should sit snugly about one inch below the bottom edge of the kneecap.
The strap needs to be adjusted to a level of tightness that is firm enough to apply pressure but not so tight that it restricts circulation or causes discomfort. Users should aim for a feeling of support without any numbness, tingling, or weakness in the lower leg. It is helpful to test the fit by bending the knee or squatting to ensure the strap stays in place and provides consistent pressure during movement.
The strap is best used only during activities that cause pain, such as running, jumping, or intense workouts, and should not be worn all day or overnight. While the strap is a helpful tool for managing symptoms, it does not replace a comprehensive rehabilitation program, including strengthening and stretching exercises. If pain persists despite proper use of the strap, consulting a physician or physical therapist is recommended to address any underlying mechanical issues.