52 y/o man was running and tripped over a metal stake in the ground. Had severe knee pain and was unable to walk afterwards.

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.

Torn Patellar Tendon

Tear of the patellar tendon can occur after intense exercise or spontaneously in patients with underlying systemic disease such as lupus, chronic renal failure and rheumatoid arthritis. Tear of the proximal end is most common as in this case. Tear of the distal tendon is the second common site of tear. Plain films can be highly suggestive when an elevated position of the patella is seen on the lateral view (patella alta).