How do patellar dislocations occur?

Patellar (i.e. knee cap) dislocations have a higher incidence rate in younger athletes. This is because they usually occur as a result of a pre-existing ligamentous laxity. The ligaments, particularly the medial patellofemoral ligament, hold the patella in the femoral/trochlear groove. As such, acute impact combined with pre-existing laxity can cause ligaments to rupture and subsequently enable the patella to dislocate. An uneven or shallow femoral groove can also increase the risk of a patellar dislocation.


What do patellar dislocations look and feel like?

Sometimes, the patella only partially dislocates. This is termed a ‘subluxation’, and is characterised by the patella slipping and immediately going back into place. A complete patella dislocation should not be confused with a knee dislocation (which involves ligament tears). It is characterised by a complete movement of the patella out of the trochlear groove. The patella usually moves back into place upon straightening the knee. The image below provides a good visualisation of the differences between a healthy patella, partial patella dislocation and complete patella dislocation.

patellar and dislocation

Symptoms that may suggest a patellar dislocation include:

  • Rapid, acute swelling
  • A sense of instability
  • Discolouration around the medial (i.e. inside) knee
  • Extreme pain until relocation occurs
  • Persistent pain at the site of the medial (i.e. inside) knee ligaments.


What are my treatment options?

Patellar dislocations can be treated both surgically and non-surgically, depending on individual factors. If non-surgical treatment is sufficient for your particular situation, your surgeon will primarily focus on strengthening your quadriceps muscle of the injured knee. The quadriceps muscle is located on the front of the thigh. Alternatively, non-surgical treatment could also involve orthotics use or stretching the structures on the outside of the knee.


If, however, you are a better candidate for surgical treatment, there are a number of different procedures that may be considered. Common procedures include tibial tubercle osteotomies (TTOs), medial patellofemoral ligament (MPFL) reconstructions and trochleoplasties. The particular operation that is selected for you will of course depend on the alignment of your knee and patella, as well as your age. Your surgeon may need CT scans, x-rays or MRIs to determine this.


Most patella stabilisation procedures will involve an additional procedure known as an arthroscopy. The role of the arthroscopy is to clean up any damage to the bone surfaces and to remove any loose fragments that may be within the joint.


References (2019). Patellar Dislocation | Orthopedics & Sports Medicine. [online] Available at: [Accessed 8 Aug. 2019]. (2019). Unstable Kneecap - OrthoInfo - AAOS. [online] Available at: [Accessed 8 Aug. 2019].