Irreducible posterolateral dislocation of the knee.

Traumatic knee dislocations are relatively rare, often associated with neurovascular injury, and almost always amenable to closed reduction. However, over the years, several authors have recognized that the rare knee dislocation not reducible by closed manipulation usually involves posterolateral dislocation of the tibia and button-holing of the medial femoral condyle through the medial retinaculum. These cases present with a dimple sign, a characteristic invagination of tissues at the medial joint line. Open reduction entails extraction of the soft-tissue collar that becomes incarcerated in the trochlea and intercondylar notch. We present an interesting case of irreducible posterolateral knee dislocation and review many of the salient points associated with this entity. Additionally, we include intraoperative video footage available on the Journal Web site to promote a better appreciation of the dramatic visual presentation and physical examination of this unusual injury.