Inclusion Criteria:  Patients treated with isolated dynamic (operation procedure according to Becher et al.using the gracilis tendon) or static MPFL plastic (operation procedure according to Schöttle et al. using the gracilis tendon). MPFL reconstruction will be performed in patients with preceding patella dislocation with: 1) a Patella-Instability-Severity (PIS) score ≤ 3 with concomitant flake fracture or 2) a PIS score ≥ 4 with clinical asymptomatic trochlea dysplasia (patella stability between 30°-60° knee flexion) without other clinically relevant static risk factors. Closed growth plates  Exclusion Criteria:  Combined procedures with trochleoplasty (high grade trochlea dysplasia, type Dejour C,D with clinical instability between 30° and 60° of knee flexion) combined procedures with cartilage transplantation High grade patellofemoral arthritis (Kellgren Lawrence score ≥3) combined procedures with femoral or tibial osteotomy Clinically eminent valgus axis (>15° valgus) Femoral internal rotation >20°, tibial external rotation >40° Instability of the cruciate or collateral ligaments Known significant musculoskeletal disease Cognitive impairment