Introduction: Dislocation after primary total knee arthroplasty is a very uncommon complication. Some case reports referred to Total Condylar, Insall Burstein or more recently Mobile bearing prostheses.

Frequency is probably under evaluated and their treatment and consequences subject to discussion.

Dislocation has to be differentiated from knee instability, subluxation and expulsion of the PE tibial insert.

The purpose of this review was to study their mechanism, treatment and consequences.

A modification of the surgical technique and the insert design was deduced.

Materials and methods: From 9/1994 to 9/1998, 229 primary Wallaby 2 with an original modular PE tibial insert were performed by the Guepar in 11 centers. Eleven posterior dislocations occurred less than 2 years postoperatively.

A prospective analysis was performed to compare the following variables of these patients (study group) to 56 cases who did not experience that complication (control group): age, sex, weight, component size, surgical approach, importance of release, pre and post surgical scores, alignment, stability, patella and component thickness. Statistical analysis of these parameters was performed.

Results: There were no statistical differences between the two groups for any variable assessed except importance of the valgus knee deformity (11° vs 6°), Keblish approach, lateral release and postoperative flexion (119° vs 106°) p< 0.01.

Conservative treatment was successful in 10 cases, but 3 recurrent dislocations and a neglected dislocation were treated surgically after modification of the tibial insert.

Discussion: Possible factors contributing to these dislocations are discussed as surgical procedure, quality of knee stability, characteristics of the tibial post compared to other implant (placement, dislocation safety factor).

After modifications of the stabilizer concerning height and slight posterior displacement, in a personal series of 129 TKA, dislocations disappeared.