MRT nach Patellaluxation: Quantifizierung der Risikofaktoren und Beschreibung der Folgeschäden

Zusammenfassung

Bei der Patellaluxation handelt es sich um ein Herausspringen der Kniescheibe aus dem trochlearen Gleitlager nach lateral. In der Regel liegen anatomische Risikofaktoren in unterschiedlichem Ausprägungsgrad vor, die in Zusammenhang mit einer Rotationsbewegung des Beines zu einem Luxationsereignis führen. Die im MRT problemlos diagnostizierbaren Kontusionsödeme der inferomedialen Patella und des lateralen Femurkondylus sowie die Ruptur des medialen patellofemoralen Ligamentes gelten als typische Zeichen einer kürzlich stattgehabten Luxation. Allerdings sind auch osteochondrale Begleitverletzungen möglich, die je nach Ausmaß eine Indikation zur frühen Refixation darstellen können. Nach dem Erstereignis folgen durch den instabilen Kapsel-Band-Apparat häufig weitere Luxationen, die in Abhängigkeit der vorliegenden anatomischen Normvarianten bis hin zu einer chronischen patellofemoralen Instabilität führen können. Therapeutisch hat sich ein breites Spektrum aus konservativen und operativen Verfahren durchgesetzt. Während Erstluxationen häufig konservativ behandelt werden, orientiert sich das operative Verfahren nach der Zweitluxation am Verletzungsmuster und Ausprägungsgrad der anatomischen Risikofaktoren. Die relevanten prädisponierenden Anlagevarianten sind die Trochleadysplasie, die Patella alta und der pathologische Abstand der Tuberositas tibia zum Sulcus trochleae (TT-TG). Insgesamt sollten im radiologischen Befund sowohl die Folgeschäden der Luxation als auch die anatomischen Risikofaktoren quantifiziert werden, da eine individuelle Analyse des zugrunde liegenden Pathomechanismus ausschlaggebend für die optimale patientenspezifische Therapie ist.

Abstract

Patellar dislocation is the lateral displacement of the patella from the femoral trochlea. Affected individuals typically have underlying anatomic risk factors of variable magnitude, which, in conjunction with leg rotation, cause the event. Magnetic resonance imaging (MRI) permits straightforward diagnosis of the typical features of recent patellar dislocation: contusion edema of the inferomedial patella and the lateral femoral condyle as well as rupture of the medial patellofemoral ligament. In case of concomitant osteochondral injury, early surgical refixation may be indicated, depending on the size. After a first dislocation, which can damage the capsuloligamentous stabilizers, subjects may sustain further dislocations or even develop chronic patellofemoral instability, depending on the presence and severity of anatomic variants. A wide range of conservative and surgical treatments are available. While a first patellar dislocation is often treated conservatively, surgical strategies after a second dislocation depend on the pattern of injury and the severity of underlying anatomic risk factors. The most relevant predisposing variants are trochlear dysplasia, patella alta, and an abnormal tibial tubercle to trochlear groove distance (TT-TG). The radiologist’s report should give a quantitative estimate of both the injuries resulting from dislocation and the underlying anatomic risk factors. An accurate characterization of the individual pathomechanism is crucial for tailoring treatment.

Key words

knee - patella - dislocation - MRI

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