Patellar tendon injury

Last night while attempting to cover first base, Angels pitcher Garrett Richards planted his left leg and then went down in a great deal of pain.  The video of the injury can be seen here, around the 1:20 mark.  If you watch closely, you will notice that when he plants his left leg, his knee is in an extreme amount of flexion (when the knee bends).  The increased amount of range of motion likely led to the significant tear or rupture of his patellar tendon.

The patellar tendon is located on the anterior (front) side of the knee.  It runs from the patella down to the tibial tuberosity, which is the bump on the anterior side of the tibia.  It's transmits force from the quadriceps to the tibia, causing the knee to extend (straighten).  Most muscle/tendon injuries occur when the structure is placed under a great deal of tension, which occurs when the muscle/tendon is being lengthened and loaded. Imagine taking a rubber band and stretching it.  As you stretch it more and more, it starts to develop small tears, and if you keep stretching it, it will eventually rupture.  Muscles and tendons behave very similarly when loaded under tension (stretching).  As the knee moves further and further into flexion, the patellar tendon continues to lengthen, and it some level of stress (or load), the tendon will start to tear and eventually rupture.  The amount of tension the patellar tendon can sustain is different for every person, but if you watch the video, you can see that his knee goes into an extreme amount of flexion in a very short period of time, which indicates a very high rate of loading.  If the patellar tendon is completely torn, it will have to be repaired surgically, and the recovery/rehab time is close to a year.  It's a devastating injury for one of the best pitcher's for the team that currently has the best record in baseball.