Joint line changes and outcomes in constrained versus unconstrained total knee arthroplasty for the type II valgus knee.

Purpose: The objective of this study was to compare the outcome of constrained and unconstrained primary total knee arthroplasty (TKA) in the management of the valgus deformity.
Methods: This is a retrospective review of patients with type II valgus knee who underwent primary TKA from 1999 to 2011. There were fifty patients in Group 1 who underwent varus-valgus constrained TKA. They were matched with another fifty patients in Group 2 who underwent unconstrained TKA.
Results: The mean joint line shift was significantly higher in Group 1 (+8 mm, SD 6 mm) than in Group 2 (+2 mm, SD 3 mm) (p = 0.03). At 2 years, there was no difference in anterior-posterior stability and mediolateral stability according to the Knee Society Score, and patients in Group 2 reported significantly better mean function score of 66.2 (SD 9.3) (mean 48, SD 7.1 in Group 1) (p = 0.002). Two patients (6 %) in Group 1 underwent revision surgery--one for a broken central peg and the other for aseptic loosening. Three patients (2 %) in Group 2 underwent revision surgery--two for global instability and one for poly wear. The estimated survivorship time was 8.3 years for constrained TKA and 12.0 for unconstrained TKA.
Conclusion: Constrained TKA was associated with more significant joint line changes for the management of valgus arthritic knee, when compared with unconstrained TKA.
Level of Evidence: Retrospective study, Level III.