Have you ever felt a pop in your knee only to look down and see your knee cap on the outside of your knee? If so, this post is for you. Learn all you need about a patella dislocation.
Guide to a Patella Dislocation
- How it happens
- How is it Diagnosed
Patella Dislocation Anatomy
Brief anatomy terms regarding the patella
- A dislocation is when the patella fully comes out of the joint and must be manually put back in
- A subluxation is a temporary event. The knee cap comes out and goes back in spontaneously
Both of these result in trauma to the same structure; the MPFL (medial patella femoral ligament0 but a dislocation usually results in more severe trauma
The primary function of the MPFL is to hold the kneecap in place and resist lateral (to the side of the body) movement
How Does A Patella Dislocation Happen?
The most common mechanism for a patella injury is rotation. In a non contact injury, the foot is planted in the ground and the rest of the body rotates away from the knee. This places force on the MPFL and the tissue fails (source). Valgus force to the knee can also cause a patellar dislocation.
In a contact injury, there is direct force to the outside of the knee. This stresses the MPFL and, like in a non contact injury, the tissue fails and the knee cap pops out.
How Is A Patella Dislocation Diagnosed?
The main diagnostic tool for a patellar dislocation is your eyes. Pretty hard to miss when your knee cap is on the side of your knee
After a patella dislocation has occurred, an MRI is the next step. This will determine the degree of damage to the MPFL and additional structures. The main concern in an isolated dislocation is damage to the cartilage underneath the knee cap.
Patella Dislocation Treatment
The initial treatment is going to be getting the patella back in place (reduction). This is a very easy technique as the patella “wants” to go back
- Apply a lateral to medial pressure to the knee
- Contract the quads
- That’s generally all it takes
The early care for any knee injury remains constant regardless of the damaged tissue
- Regain all ROM
- Restore quad function
- Restore strength
The early care guide for a knee injury can be found here.
The next step would be to restore quad function. The quads (especially the VMO) help to keep the patella in place and supplement the MPFL. The guide for some quad strengthening exercises can be found here.
Once you have restored ROM and quad function, proper rehab can be completed. This should look very similar to weight room strength training. If you have a leg strengthening program, do that.
If not, see the rehab program below
When it comes to the discussion of surgery, conservative management should ALWAYS be the first step in an isolated MPFL injury. Rehab is always sufficient to take care of an MPFL injury.
The textbook answer for when a recurring patella dislocation warrants surgery is after 2 events. The MPFL is too chronically damaged to provide any true support. This leads to repetitive trauma to the underlying cartilage under the knee cap which has long term effects
When it comes to surgery, the MPFL is artificially tightened up to restore the tensile capacity and keep the patella where it should be. See the video below