A dislocation of the kneecap or patella occurs when the knee is dislodged or knocked out of alignment from its correct position.

How happens when you have a kneecap dislocation?

Patella dislocations generally result from an inward twisting motion of the knee while the foot is on the ground/floor, or from a direct blow to the knee.The most common direction of dislocation is outward, or what we term clinically as ’lateral’.  2-3% of knee injuries are patella dislocations and most commonly occur in active young adults between the ages of fifteen to nineteen.

illustration of a kneecap dislocation

How the kneecap area is made up

A sesamoid bone is a floating bone that is held in place by a multi-layered system of connective tissue. The patella is a sesamoid bone which sits in the groove at the end of the femur. This groove is known as the ‘trochlear groove’. The knee has many layers of connective tissue and is made up of ligaments; tendons and muscles. The most important part of this system is the medial or inner part of the knee.

On this inner side, you will find the medial patella femoral ligament (MPFL) and your vastus medialis oblique (VMO) muscle that both play an important role in the controlling the position of the knee when it is at rest and during movement.

What are other causes kneecap dislocation?

The patella position is also determined by external factors, such as the alignment of the lower leg, strength around the pelvis and the structure of the groove itself.
Risk factors for dislocations have also been identified as:

  1. a history of previous dislocation;
  2. soft tissue problems i.e. weakness of VMO or tears of ligaments of the MPFL;
  3. issues with the groove itself;
  4. lower limb alignment;
  5. being a female and lastly
  6. a family history.

How to treat knee dislocations

Patella dislocations are generally treated conservatively when it’s the first time it happens, but thereafter you may need surgery if they happen again. Patients with an acute dislocation are often sent for an MRI where bone bruising can be seen. It is possible for you to put your kneecap back in place the moment it mis-aligns, but unless you are confident about doing this, a doctor should do this for you.

Once the kneecap is back in place, you need to be seen by a physiotherapist. Physiotherapy for the knee injury involves strengthening the VMO and muscles around the pelvis and correcting any external factors that may have contributed to the dislocation in the first place, such as an incorrect lower limb alignment.

If you have previously had a dislocation, or if you suspect that your leg is not aligning properly, then please book an appointment with your Physio to be evaluated.

References:

  1. Patellar Dislocation in the United States:Role of Sex,Age ,Race, and Athletic Participation.
  2. The Journal of Knee Surgery 2012; 25(01):051-058
  3. Anatomy and Biomechanics of Patellar Instability: Operative Techniques in Sports Medicine.Griewe,M.,Saifi,C.,Ahmad,C.,Gardener,T.June 2010,18(2),62-67.
  4. http://physioworks.com.au/injuries-conditions-1/patella-dislocation