Background:

Dislocation after total knee arthroplasty is a rare complication and a difficult problem to address. When the flexion gap is larger than the extension gap and the collateral ligaments are injured, instability and knee arthroplasty dislocation can occur.

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.