Kneecap Dislocation (MPFL Injury)

Knee Conditions

Kneecap Dislocation (MPFL Injury) 

Many a kneecap dislocation (MPFL injury) has happened on the sports field, but it can also happen during other activities, and as a result of an accident or mishap. The injury is painful and limits your mobility, but treatment for it is available at Sports Med London.  


The Kneecap And The MPFL 

The kneecap (patella) is one of the major bones in your knee, and it plays an important role in how your leg muscles bend the knee. The medial patellofemoral ligament (MPFL) connects your kneecap and thighbone, and it keeps the kneecap stable. Your kneecap usually glides over a groove when you bend your knee. 


Dislocation – What Happens 

Kneecap dislocation and MPFL injuries are common in the UK and further afield. It should take about 6 weeks for the injury to heal properly. 

The usual causes of the injury include suddenly changing direction when the foot is planted firmly on the ground, and a heavy blow to the knee. When your kneecap dislocates, it pops out of its groove and the tissues that keep it in place stretch or tear. 

Your kneecap might stay in a strange new position, or it might pop back into its usual place. Along with the popping sensation that you feel when that happens, you may also experience: 

  • Intense pain in your knee 
  • Not being able to straighten your knee 
  • Sudden swelling 
  • Difficulty walking 



Kneecap Dislocation Page

Diagnosing And Treating Kneecap Dislocation  

Our specialist will examine your knee and, if you experience kneecap dislocation frequently, will send you for an MRI scan or an X-ray. The scan and X-ray can help confirm the diagnosis; the latter especially in cases where the ligament has detached from the kneecap’s inner edge. 

If you are diagnosed with kneecap dislocation and MPFL injury, the treatment you are likely to be recommended is MPFL reconstruction. The procedure is performed via keyhole surgery, which means the surgeon makes small cuts. 

During the procedure, the surgeon will use a hamstring tendon taken from your body or from a donor and will pass it through a small tunnel in the kneecap and the thighbone. The surgeon then attaches the tendon to the bone using a mechanical device. 

Patients generally go home after some post-surgical monitoring, although your specialist may require you to spend the night at our clinic. You will need to use crutches for 2 to 4 weeks after your surgery. You can expect to return to your normal activities approximately 3 months after surgery. 

Find more detailed information about kneecap dislocation and MPFL injury below. 


Technical Information:

What is the MPFL (Medial patella-femoral ligament)?

The medial patellofemoral ligament is a broad structure located on the medial side (inside) of the knee joint. It connects the patella (kneecap) to the femur (thigh bone). It provides stability to the patella by acting as a restraint to any lateral displacement (outward directed force) to the patella during the early parts of knee flexion (the knee bending a few degrees from a straight position). 


How is MPFL injury diagnosed?

For patients suffering with recurrent dislocations of the patella or subluxations (almost dislocating) an MRI scan helps in confirming the diagnosis. An Xray may be useful to confirm an avulsion fracture of the medial edge of the patella (where the ligament has pulled of its bone attachment to the inner border of the kneecap). 


How is an MPFL injury treated?

An MPFL reconstruction is performed through a combination of arthroscopic (keyhole) surgery and small incisions to pass a single tendon graft (usually a single hamstring tendon ) either taken from the same patient or from a donor through a small bone tunnel in the patella and the femur where it is secured with a special mechanical device. In most cases, patients may be able to go home the same or next day partial weight bearing for between 2-4 weeks (taking some of their body weight but using crutches ) before progressing onto full weight bearing . Many patients return to their usual activities around three months after surgery.