Patella (Knee Cap) Dislocation

Patella (Knee Cap) Dislocation

Dislocation of the knee cap is a common injury in the teenage years and sometimes into the third decade. It may follow a significant twisting injury during sport or may occur following a trivial event. The dislocated patella often returns to its anatomical position (relocates) without any medical attention, leaving a painful and swollen knee. On some occasions, however, the patella does not relocate and medical attention is urgently required to place it back in position.

Body Part


The knee cap (patella) is stabilised in a groove in the thigh bone (the trochlea groove ) by ligaments on either side (patellofemoral ligaments), the depth of the groove and the alignment of the leg.


The patella usually dislocates when the foot is planted on the ground and the upper body twists away with the knee slightly bent. The first dislocation usually requires more force than subsequent events which may occur with trivial trauma.

Some individuals are more prone to dislocation than average and may have some of the following Research continues in to the understanding of the genetic and environmental factors that lead to certain individuals developing osteoarthritis.

  • General joint laxity.
  • Shallow groove for the patella (trochlea).
  • Knock knees (valhus knees).
  • Abnormal rotation of the hip and the tibia (excessive femoral anteversion and tibial torsion).
  • Symptoms

    Dislocations are painful and the knee cap normally is seen to rest on the outside of the knee. It often returns to joint when the knee is straightened but may require sedation and pain relief in a hospital to achieve this.

    The pain and swelling may remain for a few weeks. Individuals who have suffered many episodes of dislocation (chronic instability) recover much quicker from the episodes but remain apprehensive and may not fully trust their knees.


    Treatment aims at improving the patella stability. A period of rest allows the inflammation to settle down and temporary patella bracing may be helpful. It is important to start physiotherapy soon once significant cartilage injury has been excluded. Physiotherapy aims at strengthening the thigh muscles (quadriceps muscle) particularly the inside part of the muscle. Physiotherapy also aims to strengthen the hamstrings and gluteal muscles to help control the patella preventing further dislocation

    In some circumstances there is persisting instability despite good physiotherapy and these individuals normally have a structural problem which may be improved with surgery.

    If one has persisting instability a consultation with an orthopaedic surgeon is advised.