Recurrent patella Dislocation

What is Recurrent Patella Dislocation?

Recurrent patella dislocation occurs when the patella (knee cap) frequently moves sideways out of the patella groove.  The patella often moves back into the patella groove spontaneously. This can occur in one or both knees.

What is the normal structure and function of a knee joint?

The patella (knee cap) sits within a groove of the thigh bone. As the knee straightens and bends, the patella moves up and down in this groove.  This movement is called “patella tracking”. The muscle that controls this movement is the quadriceps muscle.

The quadriceps muscle is the large muscle at the front of the thigh. It is made up of four parts which attach to the patella and form a common tendon to attach to the shin bone (tibia). Contraction of the quadriceps muscle straightens the knee and moves the patella within the patella groove. One part of the quadriceps inserts into the inside of the patella and acts as a restraint to patella dislocation.

Normal tracking of the patella is a complex interplay of lower limb alignment, muscle balance, tendon and ligament attachments and patella morphology or shape.

Sometimes there is an imbalance between the structures that control the patella movement within the patella groove resulting in mal tracking or dislocation.

Patella dislocations cause weakness to the VMO and causes injury to the inner (medial) structures of the knee. This may cause the patella to track laterally (move outwards) as the knee bends and straightens and lead to increased risk of recurrent patella dislocations.

Who is more at risk of a Recurrent Patella Dislocation?

Adolescent females are more at risk of recurrent patella dislocations. Other features which also put a child more at risk of experiencing recurrent patella dislocations are:

  • Joint hypermobility (ligamentous laxity)
  • Tight lateral structures of the knee
  • Shallow patella groove
  • High sitting or small patella
  • Knock knees (genu valgum)
  • Inset Hips (femoral anteversion)

How does the injury present?

Recurrent patella dislocation is usually associated with pain, swelling and weakness.

What tests will need to be done?

MRI (Magnetic Resonance Imaging) is used to assess the anatomy of the knee in a child who experiences recurrent patella dislocations. The MRI provides detailed information about the underlying anatomy of the knee and patella. It is used to identify the child’s individual anatomy that may be putting the child more at risk of recurrent dislocation.

What is the TT – TG distance?

The TT-TG distance is a measurement taken on a MRI to assess the bony alignment of the knee in a child who experiences recurrent patella dislocations.  The Orthopaedic Surgeon uses the MRI to measure the distance between the Tibial Tuberosity and Trochlear Groove. A measurement of 20mm or greater indicates that a patients bony structure puts them at higher risk of recurrent patella dislocations.

What is the Treatment for Recurrent Patella Dislocations?

The initial treatment for recurrent patella dislocations is physiotherapy. Physiotherapy will focus on strengthening the VMO muscle using exercises. These exercises will need to be performed very consistently to effectively reduce the risk of recurrent dislocation. Ongoing VMO weakness will put a child at risk of further patella dislocations.

If your child fails to respond to appropriate physiotherapy treatment and experiences ongoing pain or patella dislocations, surgical intervention may be required.