Jumper's knee

An introduction

Background

The term “jumper's knee” was first used in 1973 to describe an insertional tendonopathy (disease of the tendon) seen in skeletally mature sportspeople. Jumper's knee usually affects the attachment of the patellar tendon to the inferior patellar pole. The definition was subsequently widened to include tendonopathy of the attachment of the quadriceps tendon to the superior patellar pole or tendonopathy of the attachment of the patellar tendon to the anterior tuberosity of the tibia. The term jumper's knee implies functional stress overload due to jumping.

Frequency

Jumper's knee is certainly one of the more common tendonopathies affecting skeletally mature sportspeople. One US study found that it occurred in as many as 20% of jumping athletes. With regard to bilateral tendonopathy, males and females are equally affected. With regard to unilateral tendonopathy, the male-to-female ratio is 2:1.

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 sportspeople, particularly those participating in jumping sports such as basketball, volleyball, or high or long jumping. Jumper's knee is occasionally found in football players, and in rare cases, it may be seen in athletes in non-jumping sports such as weight lifting and cycling.

Investigators have implicated sex, greater body weight, genu varum and genu valgum, an increased Q angle, patella alta and patella baja, and limb-length inequality as intrinsic risk factors. However, the only biomechanical impairment prospectively linked to jumper's knee is poor quadriceps 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 been implicated as extrinsic risk factors.

Interestingly, the patellar tendon experiences greater mechanical load during landing than during jumping, because of the eccentric muscle contraction of the quadriceps. Therefore, eccentric muscle action during landing, rather than concentric muscle contraction during jumping, may exert the tensile loads that lead to injury.

Symptoms

History

Jumper's knee commonly occurs in sportspeople involved in jumping sports such as basketball and volleyball. Patients report anterior knee pain, often with an aching quality. Symptom onset is insidious. Rarely is a discrete injury described.

Depending on the duration of symptoms, jumper's knee can be classified into 1 of 4 stages:

• Stage 1 - Pain only after activity, without functional impairment
• Stage 2 - Pain during and after activity, although the patient is still able to perform satisfactorily in their sport
• Stage 3 - Prolonged pain during and after activity, with increasing difficulty in performing at a satisfactory level
• Stage 4 - Complete tendon tear requiring surgical repair

Physical

Physical examination may reveal the following findings:

• Point tenderness at the inferior patellar pole, superior patellar pole, or tibial tuberosity
• Hamstring and quadriceps tightness
• Normal ligamentous stability of the knee during testing
• Normal knee range of motion
• Normal neurovascular examination
• Normal hip and ankle examination
• Intra-articular effusion of the knee (rare).