The lateral plain film shows the patella to be riding abnormally high in position. The saggital MRI images show avulsion of the patellar tendon from it's origin on the patella. Note the wavy appearance and surrounding soft tissue edema and joint effusion that is well seen on the T2-weighted image.

http://www.mritutor.org/mriteach/5201/5201.html

Findings
1-The Achilles tendon is the largest tendon in the body. It is formed from the conjoined tendons of the gastrocnemius and soleus muscles. It inserts on the posterior calcaneus.
2-The Achilles tendon contributes to plantar flexion of the foot.
3-Tears occur at the vulnerable zone of avascularity, 2-6 centimeters above the calcaneal insertion.
4-This patient’s plain film shows edema in the Kagers fat pad suggesting Achilles tendon pathology. Kager's fat pad normally presents as a lucent triangle above the superior calcaneus. The region shows abnormal soft tissue density in this patient.
5-The T2 weighted Sagittal MRI shows discontinuity of the Achilles tendon with fluid at the myotendinous junction.


http://eradiology.bidmc.harvard.edu/Classics/item.aspx?section=Emergency+Radiology&labelpk=33f0adab-853f-4010-a0e2-0756b3f1eac5&pk=37363e43-d4af-4d51-b254-632023ada1e6

Jumper's Knee refers to a spectrum of disorders that occur in patients with degeneration and/or tearing of the patellar tendon. It is one of the most common tendon abnormalities in athletically active individuals, and as the name implies, is most common in jumping athletes such as basketball and volleyball players. In the non-athlete, rheumatoid arthritis, the seronegative arthropathies, and treatment with exogenous steroids are known to predispose to this condition.

fat-suppressed proton density-weighted sagittal images in a basketball player who sustained an acute injury reveal marked edema about the patellar tendon with a fluid filled gap (arrows) at the central tendon, compatible with a complete rupture. The retracted proximal and distal ends (arrowheads) are markedly thickened, indicating severe tendinosis. The vast majority of patellar tendon ruptures occur in patients with pre-existing patellar tendinosis.

http://www.radsource.us/clinic/0612

The fat-suppressed proton density weighted sagittal view confirms the abnormally thickened and edematous tendon (arrow). Mild adjacent edema is seen within the surrounding subcutaneous and infrapatellar fat, and small interstitial splits (arrowheads) are present within the proximal tendon.
The T1-weighted sagittal images reveals marked thickening and increased signal intensity (arrow) within the patellar tendon.

http://www.radsource.us/clinic/0612

Patellar tendon tear

Normal patellar tendon

The patellar tendon is torn. It should be a smooth black stripe, as in the normal image

Here is a magnified view of the abnormality, at the front of the knee just below the patella (kneecap)