Patellar tendon fiber strains: their differential responses to quadriceps tension.

This study tested the hypothesis that the posterior fibers of the patellar tendon are subjected to higher tensile strains than the anterior fibers in response to quadriceps tension. The quadriceps tendon was loaded to 1 kN in 10 human cadaver knees and the tensile strain was measured in the anterior and posterior fibers of the patellar tendon. The central third patellar tendon was divided into anterior and posterior halves which were tensile tested to failure. The mean strain at 1 kN load was 1.7% (90 degrees flexion), 2.7% (60 degrees ), and 3.9% (10 degrees ) anteriorly, and 3.2% (90 degrees ) 4.6% (60 degrees ), and 4.9% (10 degrees ) posteriorly. Quadriceps loading caused significantly greater strains in the posterior fascicles between 60 degrees and 90 degrees knee flexion. The material properties in the anterior and posterior regions were similar, except that failure strain was significantly higher posteriorly. Thus the posterior fascicles are adapted to sustain significantly greater tensile strains before failing. This suggests that the higher overall levels of tensile strain in the posterior fibers are not sufficient to explain the clinical pattern of patellar tendonitis.