Patellofemoral instability

Patellofemoral instability is a broad and complex area of knee surgery. It is characterised clinically by recurrent patellar dislocations with an association of many different underlying anatomical pathologies that can predispose patients to the condition. These can include a tear of the medial patellofemoral ligament (MPFL), trochlear dysplasia and an increased tibial tubercle – trochlear groove distance (TT-TG). Assessing for lower limb rotational malalignment of the femur and tibia is also important in the evaluation of patellofemoral instability. A meticulous and detailed clinical assessment coupled with radiological investigations allow the clinician to identify the exact causative pathology which can often be multifactorial in some patients. It can also be associated with generalised hyperligamentous laxity and other co-morbidities including connective tissue disorders (i.e. Marfan’s syndrome, Ehlers-Danlos syndrome) which also have multisystem manifestations. A degree of supratentorial overlay is also present in some patients which can further complicate the clinical assessment and indeed should be factored into the decision-making process when considering the optimal choice of treatment. In these patients, a variable degree of catastrophizing of symptoms may be apparent and the clinician’s consultation should be prudent to this. It should be noted that undertaking patellar stabilisation surgery for the symptom of anterior knee pain alone and in the absence of true patellofemoral instability yields notoriously poor results.