Patellar tendinopathy (jumper's knee) is an overuse tendinopathy of the patellar tendon at its proximal attachment to the inferior pole of the patella.
It is common in jumping and sprinting sports: in a study of elite athletes, prevalence was about 45% in volleyball and 32% in basketball, and higher in men than women. Peak incidence is at ages 15 to 30.
Recovery takes months rather than weeks, and relapse is common if energy-storage loading is reintroduced too quickly.
The patellar tendon runs from the patella to the tibial tubercle and transmits quadriceps force to extend the knee. It stores and releases energy in the stretch-shortening cycle of landing, jumping, sprinting and cutting, with landing forces of up to 8 times body weight.
Patellar tendinopathy is an energy-storage tendinopathy, driven by repetitive high-magnitude tensile load. This distinguishes it from compressive tendinopathies such as insertional Achilles, proximal hamstring and gluteal tendinopathy. Pathology sits in the proximal posterior tendon at the inferior pole, and the adjacent, richly innervated Hoffa fat pad can become irritated alongside it.
Tendinopathy is failed healing rather than inflammation. The continuum model (Cook and Purdam) describes 3 stages: reactive (reversible), tendon dysrepair (partly reversible) and degenerative (little capacity to reverse). Loading works through mechanotransduction, which drives collagen remodelling.
Risk factors include jumping and sprinting sports, rapid increases in training load, reduced calf capacity, reduced ankle dorsiflexion and stiff landing mechanics.
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