Patellar Instability

Every time the knee bends, the patella (knee cap) glides in a groove of the femur (thigh bone) called the trochlear groove. Several soft tissue structures attach to the patella and contribute to patellar stability, including the quadriceps tendon (at the top), patellar tendon (at the bottom), and an important ligament called the medial patellofemoral ligament (MPFL) on the inside of the knee. The MPFL acts as a checkrein to guide the knee cap into the groove as the knee bends.

  • Symptoms

  • Treatment


  • Knee pain
  • Feeling of apprehension when pressure is applied to the knee cap
  • Patellar dislocations or subluxations
  • Sensation of catching under the knee cap
  • Obvious deformity in the front of the knee

Frequently Asked


How do I know if I have patellar instability?

The knee cap pops out of joint and can often pop back in on its own, but frequently the knee cap needs to be put back in place by a medical provider. After reviewing the history of the injury and a thorough physical exam, x-rays will be obtained in the office to evaluate several factors that can contribute to patella instability. Often, an MRI is ordered to ensure there are no cartilage injuries or loose bodies in the knee. An MRI allows for the evaluation of the soft tissue structures such as ligaments that stabilize the knee cap.

How do I know if I need surgery or can just manage with conservative treatment?

If a patient has only dislocated their patella one time, the injury can usually be treated without surgery unless a loose body is noted on the MRI. In cases of recurrent instability, surgery is recommended to stabilize the knee cap. Other factors that are considered when evaluating a patient for surgery are their age, activity level, and goals.

What are the risks associated with not treating my patellar instability?

The most common risks are stiffness, persistent pain, weakness, and recurrent instability. Patients who have dislocated their knee cap once have a high chance of dislocating again. These dislocation events can lead to irreversible changes to the cartilage in the knee, causing arthritis as well as fractures of the knee cap and/or thigh bone.