Dislocation of total knee arthroplasty. A report of 6 cases with 2 patterns of instability

We report 6 cases of dislocation of total knee arthroplasty (TKA). We identified 2 patterns of instability in the sagittal plane, one with posterior translation of the tibia, occurring mainly in the postoperative period and usually resulting from a trauma, and the other with anterior translation of the tibia, occurring 6 months to 7 years postoperatively and with no preceding trauma. In the latter group, instability was manifested gradually as a lengthening of the posterior cruciate ligament and the posterior capsule, leading to a recurvatum deformity of the knee.