The purpose of this study is to describe and compare the kinematic deficiencies specifically associated with each of the 3 main clinical phenotypes of patellofemoral pain syndrome. The prevalence of patellofemoral pain is high with a high rate of chronicity and recurrence and an overrepresentation of young, athletic and female populations. There are multiple classifications of patellofemoral pain syndrome. A pragmatic classification distinguishes 3 main clinical phenotypes of patellofemoral pain syndrome: with objectively displaceable patella, with extra-patellar alignment problems and without alignment problems.

The pathophysiology of patellofemoral pain syndrome is multifactorial involving static and dynamic dysfunctions of the hip, knee and foot, which remain incompletely elucidated to date. The links between the clinical and biomechanical aspects are still unclear and the kinematic and neuromuscular deficiencies associated with the 3 main clinical phenotypes are poorly understood. A validated non-invasive device allows the 3D evaluation of femorotibial rotations during walking.

The diagnostic process is based on clinical examination. The evolution of measuring tools like radios, RMI and kinematics device allows a more precise diagnostic of patellofemoral Pain syndrome. We still don't know what kind of gait parameters could help to categorize the different phenotypes. With a better understanding of these phenotypes the investigators will be able to propose a better personalized rehabilitation.

Patellofemoral pain syndrome is defined as an anterior knee pain in front of and around the patella. The diagnosis of patellofemoral pain syndrome is based on clinical examination and standard imaging.

The pathophysiology of the patellofemoral pain syndrome is multifactorial involving static and dynamic dysfunctions of the hip, knee and foot, which remain incompletely elucidated to date. The prevalence of patellofemoral pain is high with a high rate of chronicity and recurrence and an overrepresentation of young, athletic and female populations. A pragmatic classification distinguishes 3 main clinical phenotypes of patellofemoral pain syndrome: with objectively displaceable patella, with extra-patellar alignment problems and without alignment problems.

The links between the clinic and biomechanics are still unclear and the kinematics and neuromuscular impairments associated with the 3 main clinical phenotypes are poorly understood.

The KneeKG is an optoelectronic kinematic assessment device using non-invasive sensors and dedicated to real-time measurement of 3D femoro-tibial position and rotations. The kinematic, neuro-muscular, postural and proprioceptive assessments will allow us to better understand the pathophysiology of the patellofemoral pain syndrome, to establish a more accurate diagnosis of the disease, and provide a better understanding of its causes.

Several studies have shown that better adherence to exercise is associated with greater benefit in terms of pain and function in chronic pathologies.

Semi-structured interviews will enable the investigators to assess the impact of information derived from kinematic examination of the knees on adherence to treatment.

Inclusion Criteria:

• Medical diagnosis of SDFP :
• Anterior pain of the knee, mechanical, in front of and around the patella noted at more than 3/10 on a simple numerical scale (ligament or meniscal damage, synovial plicae, tendinopathies, apophysitis, neuromas, and osteoarthritis FT are differential diagnoses),
• Pain during any of the following activities: Going up / down stairs, squats, jumps, jogging, sitting, crouching.
• Duration of knee anterior pain greater than 1 month
• Affiliation to a social insurance
• Signature of the consent to participate

Exclusion Criteria:

• Neurological disorders affecting the lower extremities
• Radiographic FT osteoarthritis
• History of surgery or trauma to the lower limb less than 1 year old
• Intra-articular knee infiltration ≤ 2 months
• Cognitive or behavioral problems making it impossible to assess
• Participates in intervention research or is in the exclusion period following a previous research, if applicable
• Unable to speak, read and write French
• Patients under guardianship or curatorship,
• Patients receiving AME (French State Medical aid)