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.