Patellofemoral Pain Syndrome, pain under the knee cap, is the most common diagnosis of knee pain affecting both sedentary and active individuals. Muscle weakness in the hip and knee are often present in individuals with this diagnosis, but a cause and effect relationship between strength and knee pain has been difficult to established. In short, the research is divided on this relationship especially within the variable of hip weakness. Thus questions remain on which muscle imbalances may predispose an otherwise pain free individual for future patellofemoral pain.
A recent systematic review of the available evidence on the development of patellofemoral pain syndrome reviewed 18 studies of 4818 research participants (Neal et al. Br J Sp Med. 2019). Authors found three common groups of research subjects including military recruits, adolescents, and runners. They reported moderate to strong evidence body mass index, age, and leg alignment were not predictive of future knee pain. Interestingly, although common in clinical patients, moderate evidence reported hip weakness was not predictive of future knee pain. Authors reported quadricep weakness, especially among military recruits, was associated with future onset of knee pain.