Knee Extensor Apparatus
The extensor apparatus of the knee is composed mainly of the patellar tendon, quadriceps tendon, the patella, and its retinacula.
The quadriceps tendon. In MRI, it is mostly of low signal intensity with an anterior–posterior (a.p.) cross-sectional diameter of 5 mm. Chronic overuse can lead to repetitive episodes of inflammation and degeneration of the patellar tendon, termed “jumper’s knee” (Khan 1996). MRI shows an increase of the thickness of the patellar tendon to more than 7 mm in the a.p. direction together with signal intensity increase, obtuse (especially posterior) margins, and adjacent signal alterations in Hoffa’s fat pad (Sonin 1995).
Rupture of the patellar tendon exhibits lack of continuity on MRI and the remaining fragments of the tendon show a wavy course.
There is patella alta.
In Osgood- Schlatter disease, there is thickening and signal intensity increase in T2-weighted sequences in the distal portion of the patellar tendon close to insertion at the tibial tuberosity.
In Sinding-Larsen-Johansson disease, corresponding signal intensity alterations are present at the lower pole of the patella (Sonin 1995).