The Unstable Kneecap - the Impact of Anatomy on Function

The principal objective of the study is to find out which everyday activities make the kneecap unstable in people with patellofemoral instability. Analysing how a patient with an unstable kneecap walks will help us to determine if surgery is successful in these patients by seeing if better scores on patient questionnaires are found in patients following surgery and whether these patients also have a better pattern of walking. The investigators aim to use cameras and pressure pads to see how patients walk before and after surgery and see how this compares to patient scores on the questionnaires. If the investigators find that patients walk better after surgery they can justify that surgery is worthwhile for the patient and cost effective for the NHS.