Zusammenfassung Der „AGA Therapiealgorithmus der Patellainstabilität“ (ATAPI) basiert auf der klinischen Untersuchung, der Bildgebung und dem daraus resultierenden Risikoprofil. Im ersten Schritt wird eine mögliche Flake-Fraktur mittels Bildgebung detektiert. Im zweiten Schritt wird das individuelle Risiko einer Reluxation in Abhängigkeit der vorliegenden anatomischen und epidemiologischen Parameter erfasst. Bei niedrigem Risikoprofil ohne Flake-Fraktur wird primär die konservative Therapie empfohlen. Bei vorhandener Flake-Fraktur wird eine Refixation des Fragments angestrebt. Eine zusätzliche Rekonstruktion des medialen patellofemoralen Ligaments (MPFL) senkt das Reluxationsrisiko deutlich und wird auch als Grundpfeiler der operativen Therapie gesehen. Je nach Risikoprofil werden weitere Zusatzeingriffe in Erwägung gezogen. Somit besteht auch bei Patellaluxation ohne Flake-Fraktur aber hohem Risikoprofil die Indikation zur Operation.

Background Patellar instability has a high incidence and occurs particularly in young and female patients. If the patella dislocates for the first time, treatment is usually conservative. However, this cautious approach carries the risk of recurrence and of secondary pathologies such as osteochondral fractures. Moreover, there is also risk of continuous symptoms apparent, as recurrent patella dislocation is related to patellofemoral osteoarthritis as well. An initial surgical treatment could possibly avoid these consequences of recurrent patella dislocation. Methods A prospective, randomized-controlled trial design is applied. Patients with unilateral first-time patella dislocation will be considered for participation. Study participants will be randomized to either conservative treatment or to a tailored patella stabilizing treatment. In the conservative group, patients will use a knee brace and will be prescribed outpatient physical therapy. The surgical treatment will be performed in a tailored manner, addressing the pathologic anatomy that predisposes to patella dislocation. The Banff Patellofemoral Instability-Instrument 2.0, recurrence rate, apprehension test, joint degeneration, and the Patella Instability Severity Score will serve as outcome parameters. The main analysis will focus on the difference in change of the scores between the two groups within a 2-year follow-up. Statistical analysis will use linear mixed models. Power analysis was done for the comparison of the two study arms at 2-year follow-up with regard to the BPII Score. A sample size of N = 64 per study arm (128 overall) provides 80% power (alpha = 0.05, two-tailed) to detect a difference of 0.5 standard deviations in a t-test for independent samples. Discussion Although several studies have already dealt with this issue, there is still no consensus on the ideal treatment concept for primary patellar dislocation. Moreover, most of these studies show a unified surgical group, which means that all patients were treated with the same surgical procedure. This is regarded as a major limitation as surgical treatment of patella dislocation should depend on the patient’s anatomic pathologies leading to patellar instability. To our knowledge, this is the first study investigating whether patients with primary patella dislocation are better treated conservatively or operatively with tailored surgery to stabilize the patella. Trial registration The study will be prospectively registered in the publicly accessible database www.ClinicalTrials.gov .