The term jumper's knee was first used in 1973 to describe an insertional tendinopathy. That's a tendon injury or inflammation seen in athletes with mature skeletons at the point where the tendon attaches to bone. Jumper's knee usually involves the attachment of the kneecap tendon to the lower kneecap pole. The term also applies to injury or inflammation where the thigh muscles tendon attach to the upper kneecap pole or where the kneecap tendon attaches to the lower leg bone. Jumper's knee refers to functional stress overload due to jumping.
Jumper's knee is one of the more common tendinopathies affecting athletes with mature skeletons. It occurs in as many as 20% of jumping athletes. With regard to bilateral tendinopathy (both sides), males and females are equally affected. With regard to unilateral tendinopathy (one side), twice as many males as females are affected.
Sport Specific Biomechanics
Jumper's knee is believed to be caused by repetitive stress placed on the patellar or quadriceps tendon during jumping. It is an injury specific to athletes, particularly those participating in jumping sports such as basketball, volleyball, or high or long jumping. Jumper's knee is occasionally found in soccer players, and in rare cases, it may be seen in athletes in nonjumping sports such as weight lifting and cycling.
Risk factors include gender, greater body weight, being bow-legged or knock-kneed, having an increased angle of the knee, having an abnormally high kneecap or an abnormally low kneecap, and limb-length inequality. Impairment linked to jumper's knee includes poor quadricep and hamstring flexibility. Vertical jump ability, as well as jumping and landing technique, are believed to influence tendon loading.
Overtraining and playing on hard surfaces have also been implicated as risk factors.
Interestingly, the kneecap tendon experiences greater mechanical load during landing than during jumping, because of the eccentric (off center) muscle contraction of the quadriceps. Therefore, eccentric muscle action during landing, rather than concentric (symmetrical) muscle contraction during jumping, may exert the mechanical and tension loads that lead to injury.