Patellar tendinosis as an adaptive process: a new hypothesis.

BACKGROUND Patellar tendinosis (PT), or "jumper's knee" is a common condition in athletes participating in jumping sports, and is characterised by proximal patellar tendon pain and focal tenderness to palpation. Hypoechoic lesions observed in the proximal patellar tendon associated with the tendinosis are typically described as being a result of degenerative change or "failed healing". We propose a new model for the development of the hypoechoic lesion observed in PT, in which the aetiology is an adaptive response to differential forces within the tendon. METHODS We assessed the clinical, histopathological, and biomechanical literature surrounding the patellar tendon and integrated this with research into the response of tendons to differential forces. RESULTS AND CONCLUSIONS We propose that the hypoechoic lesion commonly described in PT is the result of adaptation or partial adaptation of the proximal patellar tendon to a compressive load. We postulate that the biomechanics of the patellar-patellar tendon interface creates this compressive environment. Secondary failure of the surrounding tensile adapted tendon tissue may result in tissue overload and failure, with resultant stimulation of nociceptors. We believe that this "adaptive model" of patellar tendinosis is consistent with the clinical and histological findings.