Instability is one of the most common reasons for total knee arthroplasty (TKA) failure. Constrained prosthesis can be used for significant ligamentous laxity, but there is not much evidence on the appropriate level of restriction for unstable varus-valgus TKA. The objective of this study was to compare the outcome and survival at a minimum follow-up of five years between rotating hinge knee prosthesis (RHK) and constrained condylar knee prosthesis (CCK) for extension instability following primary TKA.

For symptomatic extension instability after primary TKA, good functional outcomes and survival can be achieved with both designs.

Consecutive patients with unstable primary TKA who underwent revision with either RHK (n=34) or CCK (n=30) were retrospectively compared. Assessments were performed by the Knee Society Scores (KSS), and visual analogue scales (VAS) for pain and patient satisfaction. Radiological evaluation was made. Complications and re-operations were analyzed.

Mean post-operative follow-up was 10.3 (range 5-16) years for both groups. At the final follow-up, there was no significant difference between groups in the KSS-knee (p=0.228) or KSS-function (p=0.324) score, VAS-pain (p=0.563), VAS-satisfaction (p=0.780), major complication rate (p=0.194), or TKA survival at 10 years (p=0.091).

The present study showed comparable good functional outcomes and survival at long-term between RHK and CCK arthroplasties. Both designs can be recommended for revision of total knee arthroplasty with symptomatic extension instability.

Level III.