Many knee injuries begin with a snap or a pop.   Turning and twisting while running puts a lot of stress on the knee.  Most of you are aware that a pop in the knee while twisting can cause an ACL tear.   What most people are not aware of is that many athletes who felt a pop in the front of their knee during sports actually had a dislocated kneecap.  The kneecap is also called the patella.  Patella or kneecap dislocations are far more common than we thought many years ago.  There are many potential issues you need to be aware of if you had a kneecap dislocation.

Anatomy of the Kneecap

dislocated kneecapThe kneecap or patella is an oval shaped bone that sits in a groove on the front of the femur.  The groove is called the trochlea.  The kneecap stays in the trochlea groove because of two ligaments which try and prevent it from slipping out.  The ligament which appears to cause the most trouble is the medial patellofemoral ligament or the MPFL.  If the MPFL is stretched or torn, then your kneecap can dislocate.


Why Did My Kneecap Dislocate?

The stability of the kneecap is determined by:

  • the quadriceps muscles
  • the anatomy of your bones
  • the quality of the ligaments(MPFL)

All of the above contribute to hold the kneecap in place.  Your quadriceps muscles need be strong and well balanced  For that matter, so do the muscles of the hip and pelvis.  If those muscles are weak, they will affect the stability of your kneecap.

Discussing the anatomy of your kneecap and the trochlea groove that it sits in is a difficult topic to understand.  Many people have a trochlea groove in the femur that isn’t very deep.  That’s how you were born.  A “shallow” trochlea can make it easier for a patella to dislocate.

The MPFL or the medial patellofemoral ligament is the most important structure when it comes to determining why your kneecap dislocated.

dislocated kneecap Torn MPFL

How did I tear my MPFL ?

The MPFL can tear because of two different types of injuries.  First, you were running and your kneecap was struck or hit by someone.  If you are struck on the inside of your kneecap then the MPFL might tear, thus creating a dislocated kneecap.  The more common injury is that your knee was bent when you twisted and tried to turn and run.  That puts a lot of stress on the MPFL, and can cause it to tear.

We know that most ACL tears in the knee occur due to non-contact twisting or pivoting injuries.  The same is true for kneecap or patella dislocations.

How Do I Treat My Dislocated Kneecap?

In most people the kneecap will reduce or snap back into place on its own.  If you felt the knee pop and your knee looks distorted or strange then your kneecap is still dislocated.  That will require a trip to the emergency room if you do not have an Athletic Trainer to put the kneecap back into place.  The sooner the kneecap is reduced the better.

After your dislocated kneecap is reduced your knee will swell.  It will usually swell a lot.  The fluid in your knee is usually blood.  Sometimes we will aspirate or remove the blood from the knee, but that is not always necessary.

kneecap painIt is very important that you see a Sports Medicine Doctor if you suspect that you had a dislocated kneecap.  Many different injuries can occur after the dislocation.  We will need to check to make sure that you did not damage the cartilage on the kneecap or the femur.  Some cartilage injuries can be severe and require treatment sooner rather than later.  We will also be able to determine if  your MPFL is torn.

An MRI is almost always necessary after a kneecap dislocation.  The MRI will show if the cartilage has been damaged.  The MRI will also show if the MPFL is torn, and it will also tell us about the anatomy of your bones.  That means that we can tell how deep the groove is that the patella sits in.  Using the information from the MRI and from our examination we can determine the risk that you might have a second or third dislocation.

Does a kneecap dislocation require surgery?

Determining if you need surgery for a patella dislocation involves many different considerations.  We need to determine:

  • Was this your first dislocation ?
  • Was the cartilage damaged?
  • Does the cartilage need to be repaired?
  • Is your MPFL torn?
  • Does your bone anatomy affect your risk?

Most people who have had only one dislocation and do not have any cartilage damage do not need surgery.  You will be rested to let the MPFL try to heal.  Then you will be placed into physical therapy to rehabilitate the knee.

If you have a repairable cartilage injury then we will likely suggest surgery to repair the cartilage, and repair the MPFL ligament at the same time.

kneecap dislocation surgery MPFL

If you have had more than one kneecap dislocation then you will need to consider surgery to repair or reconstruct the MPFL (medial patellofemoral ligament) in order to minimize the risk of another dislocation. Each time your kneecap dislocates there is a risk that you will damage the cartilage.  It is therefore a good idea to repair the kneecap to prevent further damage after your second dislocation.

We created this video which helps you understand our decision making when we consider which operation might be best for your dislocated kneecap. 

In future posts I will go into more depth about the various surgical techniques used to prevent the patella from dislocating again.   This is a very complicated process.  Be sure that you are seeing a physician who is very experienced in managing kneecap or patella dislocations.


Dr. Howard Luks, MD – Hawthorne, NY, 19 Bradhurst Avenue, Suite 1300N, Hawthorne, NY 10532 - Phone: (914) 789-2735


About the author:

Howard J. Luks, MD

Howard J. Luks, MD

A Board Certified Orthopedic Surgeon in Hawthorne, NY. Dr Luks specializes in the treatment of the shoulder, knee, elbow, and ankle. He has a very “social” patient centric approach and believes that the more you understand about your issue, the more informed your decisions will be. Ultimately your treatments and his recommendations will be based on proper communications, proper understanding, and shared decision-making principles — all geared to improve your quality of life. Please read our Disclaimer

3 comments on “The Dislocated Kneecap: It Is More Common Than You Think

  1. Dr. Luks,

    Is it reasonable to think that a mobile top college QB, like Dondre Francois, can be at 100% within 12 months following patellar tendon repair surgery? Also, would you expect there to be little difference between the recovery rate of a top NFL skill player (receiver like Victor Cruz), and a top running college QB for this specific surgery requiring injury? Would the level of play (speed, cuts, weight etc.) have much if any difference with the exact same injury on an NFL skill guy and a top college skill guy (QB) in the length of time to recover and the expected attainment of full capacity prior to the injury?

    My reason for asking is there is information online about NFL players with patellar tendon tears and much research that concludes only 50% or the surgeries are successful and it’s tough to recover to full strength.

    Thank you.

    1. It is difficult to return to 100% of prior capacity after a patella tendon repair. It is possible to get awful close and to return to elite level sports, but it will take 12+ months and a ton of work in the gym.

      The issue is not that the patella tendon surgery fails… the tendon heals well in the majority of these cases. The issue is that it sometimes isn’t possible to achieve 100% of strength and agility following a repair. There are many psychological issue which also affect an elite athlete’s ability to return to sports after a major injury. Sometimes it is hard for them to shake off the thoughts that they can be reinjured, or the thought that they are “damaged” or “brpken”. That leaves them at risk for not be able to perform due to fear, apprehension, etc.

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