The kneecap or patella floats in position in the front of your knee.  It travels up and down in the femoral groove and is held in place by muscles and ligaments.  A pop felt during sports could mean that you dislocated your patella.  Many knee injuries cause a snap or a pop.   A dislocation of the kneecap is no different.  Turning and twisting during sports puts a lot of stress on the kneecap.  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.  A patella dislocation occurs when the bone slides out of a groove which normally holds the kneecap in place. Patella or kneecap dislocations are far more common than we thought many years ago.  A dislocation of the kneecap can lead to long term issues such as recurrent dislocations, cartilage injury or arthritic change.  The treatment of a kneecap dislocation will depend on many variables which we will review.

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:

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  • the quadriceps muscles
  • the anatomy of your bones – specifically the femoral (trochlea) groove
  • the quality of the ligaments(MPFL) that hold the patella in place.

All of the above contribute to hold the kneecap in place.

1.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.

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

3. 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 allowing the patella to slide out of place 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.  Most people who have a patella dislocation will not notice that the patella is out of place.  That is because the kneecap will often reduce or move back into place right after the dislocation.  Some of you may notice that the kneecap is out of place.  In those cases your Athletic Trainer or an Emergency Room physician will put the kneecap back into position.

How Do I Treat My Dislocated Kneecap?

The treatment for a dislocated kneecap will depend on what parts of the knee were injured when the patella came out of place.  When you dislocate the kneecap you usually tear a ligament (MPFL) which holds the patella in place (Read below for MPFL reconstruction discussion).  Many will also injure the cartilage on the patella. For some of you this is your first kneecap dislocation… for others you may have had two or three dislocations.  Depending on what structures you have injured and how many dislocations you have had will determine what your doctor will tell you regarding your treatment options.

When you dislocate your 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 pain

It 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.

Dislocated kneecap recovery time

The recovery time from a kneecap dislocation will depend on whether or not this was your first dislocation or your second or third.  Your recovery time will also depend on whether or not you have injured the cartilage on your kneecap or patella.

  • If this was your first patella dislocation and you do not have an injury to the cartilage then we usually start your physical therapy soon after the injury.  Many people will be able to return to sports in 6-12 weeks after therapy has started.
  • If this was your first dislocation and you did have a cartilage injury then you may require surgery to repair the cartilage.  That recovery process will take 4-6 months to allow the cartilage to heal.
  • If you have now had more than one dislocation then you will need to consider surgery to repair or reconstruct the MPFL ligament which holds the kneecap in place (see below).  Recovery from MPFL ligament surgery can take 6-10 months before considering a return to sports.

Does a kneecap dislocation require surgery?

Surgery for patella or kneecap dislocations can be tricky. After you have had more than one dislocation you will likely need surgery to stop the kneecap from dislocating again.  The type of surgery you need will depend on your physical examination and it will depend on your xray and MRI findings.  Many unstable kneecaps can be repaired with surgery to fix or reconstruct the MPFL ligament alone.  If you have other issues which show up on your MRI then we may need to consider additional procedures to repair your kneecap to prevent it from dislocating again.

Just to review.  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.

MPFL Reconstruction

The MPFL is the ligament in the knee which holds the patella or kneecap in its proper position.  It is the ligament which prevents the kneecap from sliding out laterally and dislocating.  If you have had recurrent patella instability, eg. you have dislocated your patella more than one time, then your MPFL is not working or has stretched out too much to function well.  In order to restore stability to your kneecap we need to consider an MPFL reconstruction.  During an MPFL reconstruction we will recreate the ligament which will stop the patella from dislocating.

In the picture below you will notice that the MPFL is attached to the kneecap and it is attached to the thigh bone or femur.

kneecap dislocation surgery MPFL

During surgery for an  MPFL reconstruction we will create a small hole in the femur.  That hole will be in a very specific place and we determine where that place is by using a special x ray machine during the surgery.  Once I determine where the hole it I will place a new ligament into that hole and secure it there with a screw.  Now that the new ligament is attached to the femur we need to attach it to the patella.  The new MPFL should have at least two attachment points on the patella.  We will usually stitch or suture that new ligament against the patella.  Overtime that new ligament will heal to the femur and the patella.

For those of you considering surgery for a patella dislocation your choice of surgeon is very important.  Not many surgeons have the experience necessary to maximize your chance of success. This can be a very challenging surgery for many people.

MPFL Reconstruction Recovery Time

After your MPFL surgery you will need time to allow for the pain and swelling to diminish.  We will brace your knee for a few weeks to limit how much you can bend it.  Within two weeks we will start your physical therapy.  You will not be able to bend the knee beyond 90 degrees for two-three weeks.  We will then allow your physical therapist to start more aggressive rehabilitation.

It will take 6-10 months to recover from an MPFL reconstruction and be able to consider a return to sports.

Take Home Message: 

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