Non traumatic posterior instability in primary total knee replacement and its revision

: La luxacion tras la artroplastia de rodilla es una complicacion poco frecuente y de dificil manejo. Una brecha en flexion demasiado grande asociada a una laxitud de los ligamentos colaterales puede llevar a la inestabilidad y a la luxacion en flexion. MATERIAL AND METHODS: We report the case of a patient presenting with a posterior dislocation of a posterior-stabilized prosthesis without trauma. Frank instability in varus stress test and a positive anterior drawer test with tibial internal rotation dismissed the conservative treatment. RESULTS: A constrained condylar prosthesis was used for the revision. He suffered a similar episode after a month, which demonstrated that the increase in the level of constraint was not enough to correct the severe asymmetric instability in flexion due to the damaged external structures. A rotating-hinge prosthesis was then implanted and the patient reported no additional episodes of instability. CONCLUSIONS: We made an exhaustive review of the literature, analyzed the possible causes that can lead to the tibiofemoral instability after a total knee arthroplasty and described some technical considerations.