The role of muscle dysfunction in patellofemoral pain : influence of different treatment approaches

Patellofemoral pain (PFP) is the most frequently diagnosed condition in patients with knee complaints and is particularly prevalent in young physically active individuals. Studies revealed that despite receiving treatment, the majority of individuals with PFP suffer from persistent complaints, indicating that current treatments fail to prevent the chronicity of symptoms. The failing long-term outcomes reflect the need to provide an update on the evidence of underlying muscular dysfunctional factors of PFP, as well as the investigation of different treatment approaches. As part of this PhD, a literature and a systematic review were conducted, which discussed the definition, risk factors, prognosis, pathophysiology and treatment of PFP. The meta-analysis showed that the majority of studies analysed muscle strength or muscular activity. Whereas, muscular dysfunctional factors such as atrophy, muscular inhibition, fatigue and flexibility remained understudied in individuals with PFP. To develop a robust and reliable test protocol for the investigation of muscular dysfunctional factors in individuals with PFP, a reliability study was performed, which enabled the development of a protocol that was applied in the following studies of the thesis. Knee braces are recommended in the acute phase of PFP. However, research on knee braces analysing the effect on stabilising the sagittal and coronal plane of the knee joint demonstrated conflicting results. Thus, the effect on lower limb biomechanics and pain of the Powers TM strap was investigated in 24 individuals with PFP and 22 healthy individuals and revealed that the Powers TM strap reduced pain and was able to modify lower limb biomechanics during functional tasks. Furthermore, a six week exercise programme for individuals with PFP was developed and investigated in 25 individuals with PFP. It could be shown that the treatment was effective to reduce pain, improve function and the functional performance of individuals with PFP. The final study of this PhD focused on the influence of acute pain on the functional performance, strength and quadriceps inhibition in 21 individuals with PFP. It was found that acute pain caused an increase of quadriceps inhibition in individuals with PFP, but did not affect functional performance or quadriceps strength. Thus, this thesis investigated the role of muscle dysfunction in PFP, explored the link to pain and showed how different treatment approaches were able to influence muscle dysfunction in individuals with PFP.