Kneecap dislocation
(Patellofemoral instability)

What is patellofemoral instability?

Patellofemoral instability is a condition where the kneecap dislocates from its bony groove in the front of the knee.

What can cause it?

Dislocations or subluxations can occur for a number of reasons.

  • Traumatic – Often the result of an injury. No underlying bony, soft tissue issues
  • Bony or soft tissue issues
  • Hypermobility/ Increased tissue laxity

What are the symptoms and signs?

  • Recurrent dislocations
  • Loss of confidence in the knee
  • Associated pain at the front of the knee
  • Composite dynamic functional assessment often reveals issues with trunk and buttock muscles along with inhibition of quadriceps musculature
  • Thigh muscle wasting/ knock knees
  • Beighton’s score may be elevated

What investigations may be required?

  • Full rotational profile assessment
  • Full-length weight-bearing X-rays with skyline patella views
  • X-rays with knee in thirty degrees of flexion
  • CT scan
  • MRI scan

These investigations are necessary to quantify the following key Patellofemoral indices:

  • Patella Alta
  • Tibial tuberosity and trochlea groove distance
  • Trochlear dysplasia
  • MPFL integrity
  • Chondral surface assessment

Click here for more information on knee dislocation surgery.

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