Instability

With a torn anterior cruciate ligament, even after all pain and swelling have settled, the patient may still experience abnormal feelings of shifting of the bones when bearing weight, and a need to taughten the thigh muscles to improve stability.

An avulsed meniscotibial ligament may leave the patient with an unstable feeling when performing twisting activities, and the knee may suddenly buckle.

Tibiofemoral instability

Knee instability (as opposed to kneecap instability) is the uncomfortable subjective experience of the knee catching, buckling (giving way), moving abnormally front-to-back, rotationally or sideways. It may be challenging to describe. The cause may be found to be -

• a problem with one or more of the soft-tissue stabilising structures of the knee
  • a torn or avulsed cruciate ligament
  • a torn anterolateral ligament
  • a torn collateral ligament
  • a torn or avulsed meniscus or meniscus root
  • an avulsed meniscotibial or meniscofemoral ligament
  • a popliteus tendon tear




• osteoarthritis with damage to the joint cartilage or the presence of cysts and spurs at the edges of the joint cartilage
  • the articular cartilage may be worn down
  • bits of joint cartilage may be floating in the joint and get caught between the bones
  • there may be a joint effusion with excessive fluid in the joint
  • bony deformity may include cysts and spurs that distort the joint anatomy
  • pain and stiffness may lead to weak muscles




• musculoskeletal imbalance such as weak quadriceps muscle or weak hip muscles

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Patello-femoral instability

A number of conditions may cause the kneecap to feel untrustworthy, where it might suddenly catch painfully or feel as if it is jumping out from its usual position, or even dislocate. These include both injury to the stabilising structure of the kneecap and abnormal anatomy between the patella and its underlying groove, including -

• torn medial patellofemoral ligament (MPFL)
• patella alta
• trochlear dysplasia
• patellar dysplasia
• poor position of attachment of patellar tendon

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