The quadriceps and patella tendons connect the muscles that straighten the knee and kick the lower leg. The thick, fibrous tissue that makes up these tendons is very resilient to injuries, but falling on a partially bent knee can cause a rupture. 

A partially severed tendon can cause severe knee swelling, while a fully severed tendon can lead to patella dislocation and the inability to walk or raise your leg straight. 

The torn tendons must be repaired surgically by cutting a small incision in the knee area. Small screws are used or holes are drilled through the patella to hold the tendon in place against the bone. The surgery usually takes about an hour. 

Afterward, the patient must wear a brace to keep the knee from bending, which could loosen the repair. Complete recovery can take 4-5 months.