In a normal knee, the kneecap slides up and down a groove (femoral groove) as the knee bends and straightens. However, this is not the case in some individuals, who may complain of a sensation of the kneecap slipping or moving out of place when the knee is in certain positions.
Abnormal sliding of the kneecap is known as ‘patellar maltracking’ and leads to pain and swelling of the knee. Patellar maltracking is more common if you are a woman but can occur in men as well. It tends to affect young adults. Two types have been described:
Primary patellofemoral instability – arises with no obvious injury. It is usually result of a combination of factors including lax ligaments, high-riding patella, a shallow groove for the kneecap to run in, or a ‘lateralized tibial tuberosity’ (The tibial tuberosity is the knobbley bit at the top of the shin bone where the tendon from the knee cap is attatched, and in some individuals it is not in line with the groove, resulting in the kneecap being pulled sideways).
Secondary patellofemoral instability - results as a complication of traumatic kneecap dislocation, usually due to rupture of the medial patellofemoral ligament.
The management of patellofemoral instability should in the first instance be nonoperative. It focuses on reducing pain and swelling, followed by a rehabilitation programme designed to treat any muscle imbalances around the knee joint. This may include retraining of the quadriceps muscles in the thigh.
Surgery may be required if there are ongoing symptoms after exhausting a non-operative approach. Further investigations will be required in order to establish factors contributing to the instability (for example a shallow groove, unbalanced ligaments, or a tibial tuberosity which is out of line with the groove). Surgery will be directed at addressing the cause of instability.
The video below shows a detailed explanation of the causes and presentation of Patellofemoral Instability. They show a basic outline of the procedures used by Amir Qureshi and after care required in order that you, the patient, may recover to your full fitness once again.