The patella or kneecap works in conjunction with the quadriceps tendon above the kneecap and the patellar or kneecap tendon below the kneecap to enable straightening and straight leg raising of the lower leg.
The patella can dislocate or slip sideways. This can occur as a result of a trauma or in patients who are susceptible to dislocation and instability of the patella.
The patellar tendon, which attaches the patella to the tibia or shinbone, can rupture, as can the quadriceps tendon, which lies above the patella.